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Controls, Diagnostics and Instrumentation

2010;():1-10. doi:10.1115/GT2010-22022.

A high temperature resistant fiber optical microphone (FOM) was developed and successfully applied in a combustion chamber at a thermal power of 8.4 kW to measure thermo-acoustic oscillations at a frequency of 85 Hz and a sound pressure level of 154 dB. The sensor head temperature was estimated to ∼ 1000 K. The core of the optical setup used for the FOM is a Fabry-Perot interferometer. To create an acoustical sensor based on this type of interferometer, a new method of generation and postprocessing of the interference signal was developed. The simple replaceability of the sensor membrane reduces the requirements concerning the sensor handling compared to conventional condenser microphones and allows the adaption of the sensor sensitivity to its application case changing the membrane stiffness.

Commentary by Dr. Valentin Fuster
2010;():11-18. doi:10.1115/GT2010-22195.

This paper describes the development and testing of a gas sampling probe that quenches chemical reactions by using supersonic expansion and helium dilution. Gas sampling probes are required for accurate measurement of exhaust emissions species, which is critical to determine the performance of an aircraft engine. The probe was designed through rounds of computational modeling and laboratory testing, and was subsequently manufactured and then tested at the University of Tennessee Space Institute (UTSI) behind a General Electric J85 turbojet engine at different power settings: idle, maximum military and afterburning. The experimental test results demonstrated that the Chemical Quick-Quench (CQQ) probe suppressed the oxidation of carbon monoxide (CO) inside the probe system and preserved more CO at afterburning conditions. In addition, the CQQ probe prevented hydrocarbons from being partially-oxidized to form CO at idle powers, and measured higher hydrocarbons and lower CO emission compared to a conventional probe at that low power condition. The CQQ probe also suppressed nitrogen dioxide (NO2 ) to nitric oxide (NO) conversion through all engine power settings. These data strongly support the conclusion that the CQQ probe is able to quench unwanted chemical reactions inside the probe for all engine power levels.

Commentary by Dr. Valentin Fuster
2010;():19-30. doi:10.1115/GT2010-22213.

During diagnostic algorithm development engine testing with implanted faults may be performed. The number of implanted faults is never large enough to truly capture the distribution in the confusion matrix. Misdiagnoses in particular are unlikely to be correctly represented. Misdiagnosis that could result in costly outcomes are frequently not captured in an implantation study, resulting in a deceptively reassuring zero value for the probability of it occurring. The Laplace correction can be applied to each element of the confusion matrix to improve the generated confidence interval. This also allows a confidence interval to be produced for zero value elements. Unfortunately, the choice of Laplace correction factor influences the size of the confidence interval, and without knowing the true distribution the best correction factor cannot be determined. The choice of correction factor depends on element probability, total sample size, number of faults and confidence level. The effect of the Laplace correction on the element probability is analytically examined to provide insight into the relative influence of the correction. This is followed by an examination of the influence of the element probability, total sample size, number of faults and confidence level on the required Laplace correction. This is achieved by sampling from known populations. A method of generating good confidence intervals on each element is proposed. This includes the production of a Laplace correction based on the sample size, number of faults and confidence level. This will allow consistent comparisons of Laplace corrected matrices rather than leaving the correction factor to each individual’s best engineering judgment.

Commentary by Dr. Valentin Fuster
2010;():31-37. doi:10.1115/GT2010-22218.

Blade fault represents one of the most frequent causes of gas turbine failures. Although various measurement methods (i.e. pressure, strain gauges, and blade tip measurements) have been found to be effective in diagnosing blade faults, it is often difficult to deploy these methods under field conditions due to the requirement of mounting sensors in the interior of a running gas turbine. Vibration spectra analysis is inevitably still represents the most widely used method for blade fault diagnosis under field conditions. However, this method is known to be only effective in detecting severe blade fault conditions (i.e. terminal rubbing); whilst, minor and transient blade faults (i.e. geometry alterations, reduction in blade tip clearance, and Foreign Object Damage (FOD) event) are often left undetected. This makes vibration spectra analysis an unreliable tool for total blade fault diagnosis in the field. This study was thus conducted to investigate methods that can improve the sensitivity and reliability of vibration analysis for blade faults diagnosis. Two novel vibration analysis methods were formulated, namely the Rotor Dynamic Wavelet Map (RDWM) and Blade Passing Energy Packet (BPEP). Experimental results showed that the time-frequency display of RDWM could provide a clearer picture of the rotor dynamic characteristics of a rotor system compared to vibration spectra. RDWM also provides a better visualization of the blade condition in the rotor and enables discrimination of various blade fault conditions (i.e. creep rub and eccentricity rub). Meanwhile, the BPEP method which breaks the overall Blade Passing Frequency (BPF) component into instantaneous and discrete energy packets of running blades in the rotor system, enables a more sensitive detection of rotor eccentricity conditions and provides early warning for impending blade rubbing which is often undetectable in the vibration spectra.

Commentary by Dr. Valentin Fuster
2010;():39-51. doi:10.1115/GT2010-22349.

Failures in gas turbines such as fretting at combustor assembly interfaces, blade rub, Thermal Barrier Coating (TBC) spalling, minor amounts of domestic or foreign object damage can be detected by mechanical vibration or gas turbine performance degradation, but it is usually too late for damage control by the time the failure is significant enough to be detected with these methods. Electrostatic charge sensors present a potential method for identifying the failure modes at an earlier stage before significant damage has occurred. In a gas turbine, there are potentially two sources of electrostatic charge in the exhaust gas flow stream: ionized plasma that is a natural byproduct of high temperature combustion, and any form of debris that has originated either in the compressor, combustor, or turbine sections of the gas turbine engine as a result of vibration or fatigue. For this reason, the electrostatic charge monitor becomes a very useful device for monitoring both combustion performance problems as well as potential damage related to debris in the exhaust stream. Electrostatic sensing technology has been proven to work in detecting ingested debris and engine debris on aerospace jet engines. However, the use of the sensors in industrial applications has shown that much research is still required especially in the areas of sensor placement and failure identification. This paper discusses results from testing conducted to identify the optimal placement location for the electrostatic charge sensors in a gas turbine exhaust stream. The results are presented for various sensor locations on small (112 kW) and medium (1.185 MW) frame gas turbines to evaluate distance, velocity, radial location, and gas turbine geometry effects. These tests are completed with the gas turbine ingesting varying amounts of TBC upstream of the compressor and administering power level changes to the gas turbine. The results of this experimental program demonstrate a clear sensitivity to sensor placement along the exhaust duct of a gas turbine as well as the radial location. There are variations in the particle flow pathlines in the exhaust duct at different gas turbine operating conditions. These variations influence the sensors response. Best results are obtained when the sensors are placed at the location with the fastest and hottest exhaust gas. Multiple sensors may be required to obtain comprehensive coverage for practical event detection.

Commentary by Dr. Valentin Fuster
2010;():53-66. doi:10.1115/GT2010-22364.

This study used a dynamic model to analyze the influence of syngas firing on the dynamic performance of the gas turbine and assessed the influence of bleeding air from the gas turbine axial flow compressor on the overall performance of the gas turbine. The dynamic model simulated the inlet air flow control using inlet guide vanes, stage by stage model of a 17-stage axial compressor, a thermodynamic model of the combustors, a lumped turbine blade cooling model, a 4-stage turbine model and a torsional shaft model. This open loop dynamic model was then controlled using control blocks that modulated the inlet guide vanes and fuel supply to facilitate stable operation using natural gas and syngas. The model investigated the impact of switching from natural gas firing to syngas firing. Influence of variation in the diluent nitrogen quantity supplied to the combustor was also analyzed.

Commentary by Dr. Valentin Fuster
2010;():67-78. doi:10.1115/GT2010-22492.

The development of measurement techniques which enable temporal and spatial highly resolved density investigations even in harsh environments is essential. Rayleigh-Scattering is a non-invasive optical measurement technique permitting such investigations. A Rayleigh-Scattering measurement system is set up, providing a new insight into fluid mechanical processes in turbo machines. In this paper Rayleigh-Scattering is used for the detection of density oscillations in the optical accessible convergent-divergent outlet nozzle of a small scale combustion test rig at various power consumptions and equivalence ratios. Until now this part of the combustion chamber is sparsely investigated due to the challenging measurement conditions. The temporal density oscillation inside the nozzle can be shown up to 4 kHz as well as its spatial distribution. Systematic errors of the setup are investigated. Spectra of pressure and density oscillations are compared. Measurements with non-reacting air flow are conducted to study flow induced density fluctuations. Entropy noise related correlations between density and pressure fluctuations are found. Therewith, the built up Rayleigh-Scattering system enables investigations of the presumed region of indirect noise generation.

Commentary by Dr. Valentin Fuster
2010;():79-88. doi:10.1115/GT2010-22496.

The operators and manufacturers of propulsion systems in the aerospace industry demand more powerful and reliable engines. In order to achieve this, a better understanding of engine aging over lifetime is required. Therefore, a performance model has been extended in order to perform feature-based performance deterioration calculations on the basis of differing operating conditions. In this paper, the main focus is brought on the influence of differing environmental and operational circumstances on the performance of a jet engine. Therefore, a detailed analysis of the aforementioned conditions was carried out for a number of regional airlines. Flight routes and destinations were evaluated in order to derive distributions for environmental parameters such as the ambient temperature and pressure altitude as well as the particle and sea salt concentration. By using details on the operational concept along with engine health monitoring data of the regarded airlines, derate distributions were set up. It could be concluded that environmental and operational conditions can be represented and characterized by statistical parameters (e.g. mean value, standard deviation) for engines that are used on regional jets. In order to connect the environmental parameters with performance parameters, a control system is necessary which transfers the environmental input to the performance program. Against this background the influence of the control system itself was analyzed. Hence, a kink point shift procedure was carried out followed by a study of the kink point shift effects. Based on previous work, the extended performance model is applied on feature-based deterioration calculations. As a result, trends of relevant performance parameters for a fleet of engines are derived. This extended calculation procedure demonstrates an approach for engine deterioration trending due to varying environmental and operational conditions.

Topics: Engines
Commentary by Dr. Valentin Fuster
2010;():89-98. doi:10.1115/GT2010-22511.

Model based diagnosis and supervision of industrial gas turbines are studied. Monitoring of an industrial gas turbine is important as it gives valuable information for the customer about service performance and process health. The overall objective of the paper is to develop a systematic procedure for modelling and design of a model based diagnosis system, where each step in the process can be automated and implemented using available software tools. A new Modelica gas media library is developed, resulting in a significant model size reduction compared to if standard Modelica components are used. A systematic method is developed that, based on the diagnosis model, extracts relevant parts of the model and transforms it into a form suitable for standard observer design techniques. This method involves techniques from simulation of DAE models and a model reduction step. The size of the final diagnosis model is 20% of the original model size. Combining the modeling results with fault isolation techniques, simultaneous isolation of sensor faults and fault tolerant health parameter estimation is achieved.

Commentary by Dr. Valentin Fuster
2010;():99-106. doi:10.1115/GT2010-22524.

Inductive sensors commonly used in Active Magnetic Bearings (AMBs) comprise soft-magnetic cores on stators and sensor targets on rotors. The rotor position is estimated based on values of inductances of sensor coils wound around the cores. These sensors are often easier to use than eddy-current sensors, but their readings can be affected by stray magnetic fields from AMB actuators. For radial sensors this problem can be mitigated by using two diametrically-opposite sensor heads in differential connection, however, the same cannot be done for axial sensors. In addition, the axial sensors often need to be located as close as possible to axial actuators, where the stray fields are higher, in order to minimize changes of the actuator operating gaps caused by differences in thermal expansions of the rotor and the stator. The axial sensor presented in this paper has been developed to address primarily the issue of sensitivity to external fields. The closest kin of the proposed sensor is the axial inductive edge sensor. Because the magnetic excitation flux in the new sensor is maintained nearly constant during the operation, it was given a name “a constant-flux edge sensor”. A prototype of the new sensor has been built and tested.

Commentary by Dr. Valentin Fuster
2010;():107-114. doi:10.1115/GT2010-22553.

In turbo machinery, clearance (the distance between the turbine or compressor blade tip to the casing) at high-pressure stages is one of the key design parameters to measure the turbine efficiency and effectiveness. Thus, appropriate modeling and prediction of the clearance under operational conditions is very important. If the clearance can be actively controlled, the turbine manufacturers get even more competitive advantages. For turbine design purpose, detailed physics based model is usually available. However, this kind of detailed model is not suitable for on-line prediction due to heavy computational requirements. Instead, a reduced order model based on the first order physics is used. Usually, the available reduced order models are computationally efficient, but they can hardly reach the accuracy desired by control engineers. In this paper, we applied an ARMA modeling technique for the reduced order clearance modeling and prediction. Typical turbine cycle operation data were used to build the ARMA model first. The built model is then used to predict other operations of the same unit, as well as other units of the same family.

Commentary by Dr. Valentin Fuster
2010;():115-123. doi:10.1115/GT2010-22568.

All over the globe, gas turbines (GTs) play tremendous role in energy and power generation. Condition monitoring is also being used to obtain early warning of impending equipment failure to prevent costly downtime and damage to process equipment. Several scheduled visits were thus made to AFAM IV, GT 18, TYPE 13D plant located near Port Harcourt, in Rivers State of Nigeria. Continuous and periodic monitoring of the thermodynamics/performance parameters such as temperature, pressure, air pumping capability and fuel flow were carried out. These activities lasted for over a period of one year on hourly basis to examine the state of health of the engine compared with the data taken. The diagnostic method of trend performance monitoring was jointly used with multiple variable mathematical models (MVMMs), because they relate deterioration to consequences. A software code-named “THAPCOM” written in C++ programming language was used proactively monitor the engine based on this MVMMs. The values observed on the third month revealed that ηO was 27.0% and AL was 48MW. A significant variation in the results obtained shows that there is a deviation between the monitored data taken from the console and the reference data in the manufacturer’s manual. These are indications of impending failure or health uncertainty of the engine. This allowed maintenance to be scheduled, or other actions taken to avoid catastrophy.

Commentary by Dr. Valentin Fuster
2010;():125-131. doi:10.1115/GT2010-22613.

The use of thermal barrier coatings (TBCs) is the key technique for realizing high-efficiency gas turbine combined cycles. Hence, TBCs are applied to various hot gas path components such as combustors, blades, and vanes. The application of a TBC causes a significant decrease in the temperature of the base metal surface. Consequently, the lifetime of the component is increased. However, it is reported that under high-temperature operating conditions, the heat resistance of the TBC decreases gradually because of sintering and erosion of the TBC layer. Accurate evaluation of changes in the TBC heat resistance is very important for evaluating the residual lifetime of a given component. We have previously developed a nondestructive technique for measuring the heat resistance of TBCs applied on the inner surface of a combustion liner. In this technique, the TBC surface is heated by a laser beam, and the temperature change of this heated point is measured by an IR camera. The heat resistance is calculated from the measured temperature. On the basis of this concept, we have made improvements to this technique so that it can be used to measure the heat resistance of a TBC layer on a blade surface. However, several difficulties are encountered when using this technique for the abovementioned purpose. For example, the blade has a three-dimensional (3D) surface and complex internal cooling paths, as opposed to the combustion liner, which has a simple cylindrical shape. Hence, it is difficult to keep the same heating condition at any surface. To overcome these difficulties, we propose a new concept and develop a system for measuring the heat resistance of the TBC layer on a blade. This system is mainly composed of a carbon dioxide laser, a robot arm, and an IR camera. In this paper, we present an overview of the developed system.

Commentary by Dr. Valentin Fuster
2010;():133-142. doi:10.1115/GT2010-22635.

Most of the techniques developed to date for module performance analysis rely on steady-state measurements from a single operating point to evaluate the level of deterioration of an engine. One of the major difficulties associated with this estimation problem comes from its underdetermined nature. It results from the fact that the number of health parameters exceeds the number of available sensors. Among the panel of remedies to this issue, a few authors have investigated the potential of using data collected during a transient operation of the engine. A major outcome of these studies is an improvement in the assessed health condition. The present contribution proposes a framework that formalises this observation for a given class of input signals. The analysis is performed in the frequency domain, following the lines of system identification theory. More specifically, the mean-squared estimation error is shown to drastically decrease when using transient input signals. The study is conducted with an engine model representative of a commercial turbofan.

Topics: Engines
Commentary by Dr. Valentin Fuster
2010;():143-153. doi:10.1115/GT2010-22642.

A challenging problem in aircraft engine health management (EHM) system development is to detect and isolate faults in system components (i.e., compressor, turbine), actuators, and sensors. Existing nonlinear EHM methods often deal with component faults, actuator faults, and sensor faults separately, which may potentially lead to incorrect diagnostic decisions and unnecessary maintenance. Therefore, it would be ideal to address sensor faults, actuator faults, and component faults under one unified framework. This paper presents a systematic and unified nonlinear adaptive framework for detecting and isolating sensor faults, actuator faults, and component faults for aircraft engines. The fault detection and isolation (FDI) architecture consists of a parallel bank of nonlinear adaptive estimators. Adaptive thresholds are appropriately designed such that, in the presence of a particular fault, all components of the residual generated by the adaptive estimator corresponding to the actual fault type remain below their thresholds. If the faults are sufficiently different, then at least one component of the residual generated by each remaining adaptive estimator should exceed its threshold. Therefore, based on the specific response of the residuals, sensor faults, actuator faults, and component faults can be isolated. The effectiveness of the approach was evaluated using the NASA C-MAPSS turbofan engine model, and simulation results are presented.

Topics: Engines
Commentary by Dr. Valentin Fuster
2010;():155-167. doi:10.1115/GT2010-22685.

This paper provides an overview of the controls and diagnostics technologies, that are seen as critical for more intelligent gas turbine engines (GTE), with an emphasis on the sensor and actuator technologies that need to be developed for the controls and diagnostics implementation. The objective of the paper is to help the “Customers” of advanced technologies, defense acquisition and aerospace research agencies, understand the state-of-the-art of intelligent GTE technologies, and help the “Researchers” and “Technology Developers” for GTE sensors and actuators identify what technologies need to be developed to enable the “Intelligent GTE” concepts and focus their research efforts on closing the technology gap. To keep the effort manageable, the focus of the paper is on “On-Board Intelligence” to enable safe and efficient operation of the engine over its life time, with an emphasis on gas path performance.

Commentary by Dr. Valentin Fuster
2010;():169-179. doi:10.1115/GT2010-22753.

This two-part study describes the development of a novel stall-detection methodology for low-speed axial-flow fans. Because aerodynamic stall is a major potential cause of mechanical failure in axial fans, effective stall-detection techniques have had wide application for many years. However, aerodynamic stall does not always result in mechanical failure; indeed, a sub-sonic fan can sometimes operate at low speeds in an aerodynamically stalled condition without incurring mechanical failure. To differentiate between aerodynamic stall conditions that constitute a mechanical risk and those that do not, the stall-detection methodology developed in the present study utilises a symmetrised dot pattern (SDP) technique. Thus, the resulting methodology is capable of differentiating between critical and non-critical conditions. The SDP for a stall condition is different from that for a non-stall condition providing a basis for differentiation of the two. Part I of this study establishes the stall characteristics of a low-speed fan using flush-mounted microphones placed at four azimuthal positions around the casing of a fan. Acoustic data are collected from these positions at full-, half-, and quarter-speed. These data are then processed to establish, for each speed, regions of: (i) stable aerodynamic operation; (ii) stall incipience; and iii) rotating stall. Spatial and temporal correlations between rotating instabilities are established, which facilitates a full analysis of stall inception. Part II of the study describes a stall-warning criterion based on visual waveform analysis and the stall-detection methodology that subsequently emerges from the analysis.

Commentary by Dr. Valentin Fuster
2010;():181-190. doi:10.1115/GT2010-22754.

This two-part study describes the development of a novel stall-detection methodology for low-speed axial-flow fans. Because aerodynamic stall is a major potential cause of mechanical failure in axial fans, effective stall-detection techniques have had wide application for many years. However, aerodynamic stall does not always result in mechanical failure. A sub-sonic fan can sometimes operate at low speeds in an aerodynamically stalled condition without incurring mechanical failure. To differentiate between aerodynamic stall conditions that constitute a mechanical risk and those that do not, the stall-detection methodology in the present study utilises a symmetrised dot pattern (SDP) technique that is capable of differentiating between critical and non-critical conditions. The SDP for a stall condition is different from that for a non-stall condition providing, a basis for differentiation of the two. Part I of this study presented the azimuthal experimental data which established the stall characteristics of a variable-speed fan. Part II describes a stall-warning criterion based on an SDP visual waveform analysis and developed stall-detection methodology based on that analysis. The study presents an analysis of the acoustic and structural data across the nine aerodynamic operating conditions represented in a 3 × 3 matrix combination of: (i) three speeds (full-, half-, and quarter-speed) and (ii) three operational states (stable operation, incipient stall and rotating stall). This differentiates critical stall conditions (those that will lead to mechanical failure of the fan) from non-critical ones (those that will not result in mechanical failure), thus providing a basis for an intelligent stall-detection methodology.

Commentary by Dr. Valentin Fuster
2010;():191-200. doi:10.1115/GT2010-22818.

This paper presents an algorithm that automatically identifies and extracts steady-state engine operating points from engine flight data. It calculates the mean and standard deviation of select parameters contained in the incoming flight data stream. If the standard deviation of the data falls below defined constraints, the engine is assumed to be at a steady-state operating point, and the mean measurement data at that point are archived for subsequent condition monitoring purposes. The fundamental design of the steady-state data filter is completely generic and applicable for any dynamic system. Additional domain-specific logic constraints are applied to reduce data outliers and variance within the collected steady-state data. The filter is designed for on-line real-time processing of streaming data as opposed to post-processing of the data in batch mode. Results of applying the steady-state data filter to recorded helicopter engine flight data are shown, demonstrating its utility for engine condition monitoring applications.

Commentary by Dr. Valentin Fuster
2010;():201-213. doi:10.1115/GT2010-22851.

Atmospheric turbulence models are necessary for the design of both inlet/engine and flight controls, as well as for studying integrated couplings between the propulsion and the vehicle structural dynamics for supersonic vehicles. Models based on the Kolmogorov spectrum have been previously utilized to model atmospheric turbulence. In this paper, a more accurate model is developed in its representative fractional order form, typical of atmospheric disturbances. This is accomplished by first scaling the Kolmogorov spectral to convert them into finite energy von Karman forms. Then a generalized formulation is developed in frequency domain for these scale models that approximates the fractional order with the products of first order transfer functions. Given the parameters describing the conditions of atmospheric disturbances and utilizing the derived formulations, the objective is to directly compute the transfer functions that describe these disturbances for acoustic velocity, temperature, pressure and density. Utilizing these computed transfer functions and choosing the disturbance frequencies of interest, time domain simulations of these representative atmospheric turbulences can be developed. These disturbance representations are then used to first develop considerations for disturbance rejection specifications for the design of the propulsion control system, and then to evaluate the closed-loop performance.

Commentary by Dr. Valentin Fuster
2010;():215-221. doi:10.1115/GT2010-22904.

We describe our range of high temperature (1100°C) pressure sensors capable of measuring both static pressures of several Bar as required by gas turbine and jet engines, and measuring dynamic pressure fluctuations with a total dynamic range of in excess of 100000. This is achieved by a combination of rugged sensor design and our proprietary optical interrogator. This allows operation in harsh environments, EMI immunity, and simultaneous interrogation of not only static and dynamic pressure, but also the temperature of the sensor. This allows the sensor to maintain high accuracy over a wide range of operating temperatures. To date sensors have not been able to offer operation temperatures this high whilst enabling accurate dynamic pressure readings at the locations required. Also the static pressure cannot be retrieved simultaneously in real time from the same sensor. Also the temperature coefficient of the sensor has to be taken into account by measuring the temperature the sensor is operating at. Oxsensis has addressed these issues and we will present results showing dynamic pressure and temperature and explain how we can measure the temperature of the sensor with our interrogation schemes. We will describe the form of the sensor and the test data confirming its suitability for harsh environments. We will also explain the optical interrogator performance and present simulated results. The interrogator may be realised by a slave cavity or preferably on an integrated optical platform. As these sensors are intended for hostile gas turbine and aerospace environments, we will also present data from real life engine trials that we have performed, and compare the data we obtained with existing measurement techniques. Tests on a combustor rig have tested the sensor up to 1000°C, demonstrating that using our sensors in an engine at these temperatures is a realistic prospect. We believe that the ruggedness and performance of these sensors together with our complimentary interrogators mean that they are of significant interest to instrumentation of gas turbine engines and in the future the development of sophisticated engine feedback and emission control schemes, both in land based and aerospace environments.

Commentary by Dr. Valentin Fuster
2010;():223-233. doi:10.1115/GT2010-22920.

A new probe has been developed to measure the time averaged stagnation temperature, stagnation pressure and gas composition. This probe can be used in the high temperature regions of gas turbines, including downstream of the combustor and in the first stages of the high pressure turbines, as well as in other environments. The principal benefits of the new probe are that it overcomes the limitations of the standard methods that are used to measure temperature in high temperature environments and that it replaces three separate probes, for the three quantities mentioned above, with one single probe. A novel method of measuring temperature is used, which improves upon the accuracy of thermocouples and increases the temperature operating range. The probe consists of a choked nozzle placed in the hot flow at the point of interest. The working principle is based on the theory that for a choked nozzle, there is a fixed relationship between the stagnation quantities, the gas characteristics and the mass flow rate through the nozzle. The probe has an aspirated phase, where the gas composition and the mass flow rate are measured and a stagnated phase, where the stagnation pressure is measured. The stagnation temperature is determined from the above quantities. The operating principle has been proven valid through laboratory and rig tests. The probe has been successfully tested in a Rolls-Royce Viper engine up to 1000K and 2 bar and in a combustor rig up to 1800K and 4 bars. Measurements of stagnation temperature, stagnation pressure and gas compositions for these tests are presented in the paper and are compared with reference measurements. The accuracy of stagnation pressure and gas composition measurements is equal to the accuracy achievable with techniques that are commonly used in gas turbines. The estimated achievable accuracy of the aspirated probe in terms of temperature measurements is ±0.6%, i.e. ±10K at 1800K, which improves upon the accuracy of temperature measurements performed with standard thermocouples at the same temperatures, the uncertainty of which could be as high as ±2%.

Commentary by Dr. Valentin Fuster
2010;():235-243. doi:10.1115/GT2010-22944.

The CF-18 aircraft is a complex system for which a variety of data are systematically being recorded: operational flight data from sensors and Built-In Test Equipment (BITE) and maintenance activities recorded by personnel. These data resources are stored and used within the operating organization but new analytical and statistical techniques and tools are being developed that could be applied to these data to benefit the organization. This paper investigates the utility of readily available CF-18 data to develop data mining-based models for prognostics and health management (PHM) systems. We introduce a generic data mining methodology developed to build prognostic models from operational and maintenance data and elaborate on challenges specific to the use of CF-18 data from the Canadian Forces. We focus on a number of key data mining tasks including: data gathering, information fusion, data pre-processing, model building, and evaluation. The solutions developed to address these tasks are described. A software tool developed to automate the model development process is also presented. Finally, the paper discusses preliminary results on the creation of models to predict F404 No. 4 Bearing and MFC (Main Fuel Control) failures on the CF-18.

Commentary by Dr. Valentin Fuster
2010;():245-256. doi:10.1115/GT2010-23010.

In order to advance the technology for measurements in higher temperature flows, a novel miniature (diameter 2.5 mm) fast response probe that can be applied in flows with temperatures of up to 533K (500°F) has been developed. The primary elements of the probe are two piezoresistive pressure transducers that are used to measure the unsteady pressure and unsteady velocity field, as well as the steady temperature. Additional temperature and strain gauge sensors are embedded in the shaft to allow a much higher degree of robustness in the use of this probe. The additional temperature sensor in the shaft is used to monitor and correct the heat flux through the probe shaft, facilitating thermal management of the probe. The strain gauge sensor is used to monitor and control probe shaft vibration. Entirely new packaging technology had to be developed to make possible the use of this probe at such high temperatures. Extensive calibration and thermal cycling of the probe used to bound the accuracy and the robustness of the probe. This novel probe is applied in the one-and-1/2-stage, unshrouded axial turbine at ETH Zurich; this turbine configuration is representative of a high work aero-engine. The flow conditioning stretch upstream of the first stator is equipped with a recently designed hot streak generator. Several parameters of the hot streak, including temperature, radial and circumferential position, and shape and size can be independently controlled. The interactions between the hot streak and the secondary flow present a perfect scenario to verify the probe’s capability to measure under real engine conditions. Therefore, measurements with the novel probe have been made in order to prove the principle and to detail the interaction effects with blade row pressure gradients and secondary flows.

Commentary by Dr. Valentin Fuster
2010;():257-265. doi:10.1115/GT2010-23075.

In modern gas turbine health monitoring systems, the diagnostic algorithms based on gas path analysis may be considered as principal. They analyze gas path measured variables and are capable of identifying different faults and degradation mechanisms of gas turbine components (e.g. compressor, turbine, and combustor) as well as malfunctions of the measurement system itself. Gas path mathematical models are widely used in building fault classification required for diagnostics because faults rarely occur during field operation. In that case, model errors are transmitted to the model-based classification, which poses the problem of rendering the description of some classes more accurate using real data. This paper looks into the possibility of creating a mixed fault classification that incorporates both model-based and data-driven fault classes. Such a classification will combine a profound common diagnosis with a higher diagnostic accuracy for the data-driven classes. A gas turbine power plant for natural gas pumping has been chosen as a test case. Its real data with cycles of compressor fouling were used to form a data-driven class of the fouling. Preliminary qualitative analysis showed that these data allow creating a representative class of the fouling and that this class will be compatible with simulated fault classes. A diagnostic algorithm was created based on the proposed classification (real class of compressor fouling and simulated fault classes for other components) and artificial neural networks. The algorithm was subjected to statistical testing. As a result, probabilities of a correct diagnosis were determined. Different variations of the classification were considered and compared using these probabilities as criteria. The performed analysis has revealed no limitations for realizing a principle of the mixed classification in real monitoring systems.

Commentary by Dr. Valentin Fuster
2010;():267-276. doi:10.1115/GT2010-23146.

A variety of PID control tuning rules have been proposed for single-input single-output systems, but there is still a lack of research on PID controller design for multi-input multi-output systems. The objective in this paper is to gain some insight into multi-variable PID controller design for gas turbine engines. First of all, we present an approach to design multi-variable PID controllers based on the pole placement technique in the framework of linear matrix inequalities. Then this paper makes a comparison of four multi-variable PID controller design methods including pole-placement, iterative LMI approach, cone complementarity, and sufficient LMI condition. In terms of numerical computation, control performance, and anti-disturbance, we make an attempt to evaluate their performance and give some guidelines to gas turbine engine control. Experimental results illustrate that the pole-placement and iterative LMI methods are slightly superior to others due to their robust performance and their ease of solution and implementation.

Commentary by Dr. Valentin Fuster
2010;():277-285. doi:10.1115/GT2010-23147.

This paper presents an approach to automatic tuning of the parameters of a PID controller for the multivariable gas turbine engine control, taking into account amplitude saturation and model nonstrict-properness. First of all, we illustrate that the PID controller design problem can be transformed into seeking a static output feedback controller for some augmented state-space model. Then we compute an initial stabilizable parameters of the involved PID controller in the strictly proper case, using a well-known static output feedback algorithm. As far as a non-strictly proper model is concerned, this paper uses a degenerate linear transformation to change its output equation into a strictly proper form. The drawback of the initially computed PID controller lies in its high gains (triggering amplitude saturation) that prevent it from being applicable to practical gas turbine engine control. In this paper, we build on a linear matrix inequality (LMI) based antiwindup scheme to address the constraints from amplitude saturation. Both of these problems are formulated in the LMI framework and can be efficiently solved using off-the-shelf software. Experimental results show the promising performance of the proposed method.

Commentary by Dr. Valentin Fuster
2010;():287-297. doi:10.1115/GT2010-23226.

Controls systems are an increasingly important component of turbine-engine system technology. However, as engines become more capable, the control system itself becomes ever more constrained by the inherent environmental conditions of the engine; a relationship forced by the continued reliance on commercial electronics technology. A revolutionary change in the architecture of turbine-engine control systems will change this paradigm and result in fully distributed engine control systems. Initially, the revolution will begin with the physical decoupling of the control law processor from the hostile engine environment using a digital communications network and engine-mounted high temperature electronics requiring little or no thermal control. The vision for the evolution of distributed control capability from this initial implementation to fully distributed and embedded control is described in a roadmap and implementation plan. The development of this plan is the result of discussions with government and industry stakeholders.

Commentary by Dr. Valentin Fuster
2010;():299-306. doi:10.1115/GT2010-23228.

Gas turbines are the main power producing components in combined cycle and simple cycle power plants. A gas turbine trip is a rapid uncontrolled shutdown of the turbine that is initiated by the turbine controller to protect it from failures. The turbine loses significant amount of life due to strong thermal transients during a trip and the utility company loses revenue because of lost power generation. Therefore, prediction of trips has significant financial impact. This paper presents a method to predict gas turbine trips due to electro hydraulic control valve system failures. This paper also provides methods to detect gas control valve system failures in their incipient phase and methods to identify various failure signatures for diagnostics. The methodology presented here could be extended beyond the current application to other causes of trips in the gas turbine, thereby impacting availability and reliability of the turbine.

Commentary by Dr. Valentin Fuster
2010;():307-317. doi:10.1115/GT2010-23262.

A method giving the possibility for a more detailed gas path component fault diagnosis, by exploiting the “zooming” feature of current performance modelling techniques, is presented. A diagnostic engine performance model is the main tool that points to the faulty engine component. A diagnostic component model is then used to identify the fault. The method is demonstrated on the case of compressor faults. A 1-D model based on the “stage stacking” approach is used to “zoom” into the compressors, supporting a 0-D engine model. A first level diagnosis determines the deviation of overall compressor performance parameters, while “zooming” calculations allow a localization of the faulty stages of a multistage compressor. The possibility to derive more detailed information with no additional measurement data is established, by incorporation of empirical knowledge on the type of faults that are usually encountered in practice. Although the approach is based on known individual diagnostic methods, it is demonstrated that the integrated formulation provides not only higher effectiveness but also additional fault identification capabilities.

Topics: Fault diagnosis
Commentary by Dr. Valentin Fuster
2010;():319-329. doi:10.1115/GT2010-23442.

In this paper, a novel real-time fault detection and isolation (FDI) scheme that is based on the concept of multiple model approach is proposed for jet engines. A modular and a hierarchical architecture is proposed which enables the detection and isolation of both single as well as permanent concurrent faults in the engine. The nonlinear dynamics of the jet engine is linearized in which compressors and turbines maps are used for performance calculations and a set of linear models corresponding to various operating modes of the engine (namely healthy and different fault modes) at each operating point is obtained. Using the multiple model approach the probabilities corresponding to each operating point of the engine are generated and the current operating mode of the system is detected based on evaluating the maximum probability criteria. It is shown that the proposed methodology is also robust to the failure of pressure and temperature sensors and extensive levels of noise outliers in the sensor measurements. Simulation results presented demonstrate the effectiveness of our proposed multiple model FDI algorithm for both structural faults and actuator fault in the jet engine.

Commentary by Dr. Valentin Fuster
2010;():331-342. doi:10.1115/GT2010-23478.

This paper details the development of a prototype in-flight foreign object damage (FOD) detection system through various stages, resulting in a system capable of detecting objects as small as one gram (1g) mass. The system comprises an eddy current sensor based tip timing system and acoustic emissions vibration sensors controlled through a digital signal processor (DSP). QinetiQ have developed light weight, contamination-immune eddy current tip timing sensors for use in engine health management. Engine tests confirmed these sensors’ potential for detecting FOD events. FOD detection algorithms were developed and implemented in a prototype DSP that was built and tested on an uninstalled gas turbine engine. The trials showed that the prototype DSP FOD detection system could detect dynamic FOD events at full engine speed. Further work was carried out to enhance the FOD detection system, overcoming limitations in the previous system through the implementation of enhanced algorithms and its extension to accept four eddy current sensor inputs as well as a vibration signal input from an acoustic emissions (AE) sensor. An algorithm that computes engine speed from the tip timing data was also implemented to alleviate the need for a separate 1/rev signal. A number of engine trials were successfully completed in order to validate the system. The speed algorithm has been successfully validated on engine trials and comparisons with a conventional optical based 1/rev showed the DSP-generated 1/rev signals to be almost identical to the conventional system. Typically, the error was in the region of 0.03% speed. The investigations culminated in a test series designed to ascertain the system’s sensitivity to foreign object impacts. These demonstrated that the system was capable of detecting objects down to one gram (1g) mass introduced at low speed into the engine intake.

Topics: Gas turbines , Testing
Commentary by Dr. Valentin Fuster
2010;():343-351. doi:10.1115/GT2010-23517.

The thermal history of hot surfaces is of great practical importance, but very hard to measure. Thermal indicating paints offer one possible and practical way, but they have many disadvantages. A novel concept for the utilisation of phosphorescent coatings as thermal history sensors has been proposed by Feist et al. [1] in 2007. These phosphor coatings undergo irreversible changes when exposed to high temperatures that affect their light emission properties. A subsequent off-line analysis of the emission at room temperature can reveal the temperature history of the coating. In this paper, an investigation of the amorphous-to-crystalline change of Y2 SiO5 : Tb is reported and used to provide a proof of concept for a phosphorescent thermal history sensor. The phosphor powder was calcined at different temperatures, and characterised using photoluminescence spectroscopy. A calibration curve was generated from the measurements and is presented and discussed.

Topics: Sensors
Commentary by Dr. Valentin Fuster
2010;():353-363. doi:10.1115/GT2010-23539.

Traditional engine health management development has focused on major gas turbine engine components (i.e., disks, blades, bearings, etc.) due to the fact that these components are expensive to maintain and their failures frequently have safety implications. However, the majority of events that lead to standing down of aircraft arise from gas turbine accessory components such as pumps, generators, auxiliary power units, and motors. Common vibration diagnostics, which are based on frequency domain analysis that assumes the monitored signal is “stationary” during the analysis period, are not effective for these components. This is true because operating conditions are often non-stationary and evolving, which leads to spectral smearing and erroneous analysis that can cause missed detections and false alarms. Traditionally, this is avoided by defining steady state operating conditions in which to perform the analysis. Although this may be acceptable for major engine components, which are typically highly loaded during normal steady operation, many engine accessories are only high loaded during transients, especially startup. For example, an engine starter or fuel pump may be more highly loaded and therefore susceptible to damage during engine start up, typically avoided by traditional vibration analysis methods. More importantly, certain component faults and their progression can also lead to non-stationary vibration signals that, because of the smearing they induced, would be missed by traditional techniques. As a result, the authors have developed a novel engine accessory health monitoring methodology that is applicable during non-stationary operation through application of joint time-frequency analysis (JTFA). These JTFA approaches have been proven in other disciplines, such as speech analysis, radar processing, telecommunications, and structural analysis, but not yet readily applied to engine accessory component diagnostics. This paper will highlight the results obtained from applying JTFA techniques, including Short-Time Fourier Transform, Choi-Williams Distribution, Continuous Wavelet Transform, and Time-Frequency Domain Averaging, to very high frequency (VHF) vibration data collected from healthy and damaged turbine engine accessory components. The resulting accuracy of the various approaches were then evaluated and compared with conventional signal processing techniques. As expected, the JTFA approaches significantly outperformed the conventional methods. On-board application of these techniques will increase prognostics and health management (PHM) coverage and effectiveness by allowing accessory health monitoring during the most life influencing regimes regardless of operating speed and reducing inspection and replacement costs resulting in minimizing the vehicle down time.

Commentary by Dr. Valentin Fuster
2010;():365-376. doi:10.1115/GT2010-23586.

This paper presents a novel methodology for fault detection in gas turbine engines based on the concept of dynamic neural networks. The neural network structure belongs to the class of locally recurrent globally feed-forward networks. The architecture of the network is similar to the feed-forward multi-layer perceptron with the difference that the processing units include dynamic characteristics. The dynamics present in these networks make them a powerful tool useful for identification of nonlinear systems. The dynamic neural network architecture that is described in this paper is used for fault detection in a dual-spool turbo fan engine. A number of simulation studies are conducted to demonstrate and verify the advantages of our proposed neural network diagnosis methodology.

Commentary by Dr. Valentin Fuster
2010;():377-383. doi:10.1115/GT2010-23588.

Legacy processes sometimes include steps that have no clear justification and add unnecessary cost that too often no one can explain. An example of this is the costly step of adding temporary copper leads for engine strain gage calibration. In an attempt to eliminate temporary leads, gage calibration was performed with the permanent type-K thermocouple engine lead wire. This cost saving effort resulted in uncovering a source of measurement noise and error signals in engine development data. Subsequent laboratory studies showed that type-K thermocouple wire produces sinusoidal error signals as a function of vibration input. These error signals have the potential to add coherently to the strain gage information causing the measured amplitude to be either higher or lower as a function of phase between the signals. The laboratory studies also compared different wire alloys and their associated signal generating properties in order to identify suitable replacement wire. Final validation of the new lead wire was accomplished by running an engine test and producing a back-to-back comparison of type-K to the replacement lead wire. This test compared pairs of dynamic strain gages on separate airfoils installed at the same locations. Test data recorded with the gage excitation current turned off showed the replacement wire eliminated all wire-generated signals above 0.25 ksi (1,724 kPa), while the type-K leads generated signals up to 2.5 ksi (17,237 kPa). Test data with strain gages energized showed a dramatic reduction in false signals and noise with the replacement lead wire. The data collected through the type-K wire illustrates the potential for making poor design choices when wire-generated signals are undetected in the data. This work resulted in measurable cost savings (millions of dollars) by introducing a replacement for type-K wire which eliminated the need for temporary leads. While the cost avoidance here can be difficult to estimate, preventing a field failure resulting from erroneous data could result in orders of magnitude more cost saving.

Commentary by Dr. Valentin Fuster
2010;():385-400. doi:10.1115/GT2010-23630.

This paper presents the first experimental engine and test rig results obtained from a fast response cooled total pressure probe. The first objective of the probe design was to favor continuous immersion of the probe into the engine to obtain time series of pressure with a high bandwidth and therefore statistically representative average fluctuations at the blade passing frequency. The probe is water cooled by a high pressure cooling system and uses a conventional piezo-resistive pressure sensor which yields therefore both time-averaged and time-resolved pressures. The initial design target was to gain the capability of performing measurements at the temperature conditions typically found at high pressure turbine exit (1100–1400K) with a bandwidth of at least 40kHz and in the long term at combustor exit (2000K or higher). The probe was first traversed at the turbine exit of a Rolls-Royce Viper turbojet engine, at exhaust temperatures around 750 °C and absolute pressure of 2.1bars. The probe was able to resolve the high blade passing frequency (≈23kHz) and several harmonics up to 100kHz. Besides the average total pressure distributions from the radial traverses, phase-locked averages and random unsteadiness are presented. The probe was also used in a virtual three-hole mode yielding unsteady yaw angle, static pressure and Mach number. The same probe was used for measurements in a Rolls-Royce intermediate pressure burner rig. Traverses were performed inside the flame tube of a kerosene burner at temperatures above 1600 °C. The probe successfully measured the total pressure distribution in the flame tube and typical frequencies of combustion instabilities were identified during rumble conditions. The cooling performance of the probe is compared to estimations at the design stage and found to be in good agreement. The frequency response of the probe is compared to cold shock tube results and a significant increase in the natural frequency of the line-cavity system formed by the conduction cooled screen in front of the miniature pressure sensor were observed.

Commentary by Dr. Valentin Fuster
2010;():401-407. doi:10.1115/GT2010-23640.

For several years, the potential benefits of implementing a distributed-control system on an airborne gas-turbine engine have been discussed and analyzed. However, after many years of trade studies and lab demonstrations, it appears that the airborne gas-turbine community is no closer to implementing this type of distributed architecture. The NASA-sponsored Distributed Engine Control Working Group is attempting to unify the efforts of engine manufacturers, their system integrators, and sub-tier suppliers. In order to collectively move forward, it is necessary to understand the issues that have impeded the progress of this approach. In so doing, the industry can focus on the near-term work required to develop programs that would create the necessary infrastructure to make airborne turbine-engine-based distributed-control systems a reality. This paper will present some proposed distributed-control architectures, advantages and disadvantages of some of these approaches, and will discuss the major technical challenges that have, to date, prevented these architectures from becoming viable. Some of the architectural approaches range from a fully distributed system (one distributed-control module per actuator loop) to a “hybridized” system that has a data concentrator and a reduced FADEC. The technical challenges that will be discussed include: high-temperature electronics, robust serial-communication bus in a high-temperature environment, power distribution, and certification.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2010;():409-415. doi:10.1115/GT2010-23651.

This study presents early results for a localized, in-situ sensing approach for detecting cracks in turbine engines. A wireless slip ring system was developed for capturing and transmitting acoustic emissions data from rotors during operation. The wireless communication between the rotor and the stator is accomplished through capacitive coupling. The antennas are fashioned as a ring within a ring set-up. Here, tests were conducted under both static and rotating conditions in order to document the abilities of the system concerning signal accuracy after modulation and demodulation. Results showed that the prototype wireless slip ring was able to accurately recreate fixed frequency or arbitrary input signals, generated using a pulse/function generator or lead breaks imitating fracture events, in the frequency range of a few hundred Hz to 850 KHz. Planned improvements as well as strategies for implementation are also discussed.

Topics: Rotors
Commentary by Dr. Valentin Fuster
2010;():417-427. doi:10.1115/GT2010-23749.

Gas turbine health monitoring includes the common stages of problem detection, fault identification, and prognostics. To extract useful diagnostic information from raw recorded data, these stages require a preliminary operation of computing differences between measurements and an engine baseline, which is a function of engine operating conditions. These deviations of measured values from the baseline data can be good indicators of engine health. However, their quality and success of all diagnostic stages strongly depend on an adequacy of the baseline model employed and, in particular, on mathematical techniques applied to create it. To create the baseline model we have applied polynomials and the least square method for computing their coefficients over a long period of time. Some methods were proposed to enhance such a polynomial-based model. The resulting accuracy was sufficient for reliable monitoring gas turbine deterioration effects. The polynomials previously investigated enough are used in the present study as a standard for evaluating artificial neural networks, a very popular technique in gas turbine diagnostics. The focus of this comparative study is to verify whether the use of networks results in a better description of the engine baseline. Extensive field data of two different industrial gas turbines were used to compare these two techniques in various conditions. The deviations were computed for all available data and quality of the resulting deviations plots was compared visually. A mean error of the baseline model was an additional criterion for the comparing the techniques. To find the best network configurations many network variations were realized and compared with the polynomials. Although the neural networks were found to be close to the polynomials in accuracy, they could not exceed the polynomials in any variation. In this way, it seems that polynomials can be successfully used for engine monitoring, at least for the analyzed gas turbines.

Commentary by Dr. Valentin Fuster

Cycle Innovations

2010;():429-436. doi:10.1115/GT2010-22031.

The advanced mathematical model of Solid Oxide Fuel Cell (SOFC) is presented. Electrochemical, thermal, electrical and flow parameters are collected in the 0D mathematical model. The aim was to combine all cell working conditions in as low number factors as possible, which can be relatively easy to determine. A validation process for various experimental data was made and adequate results are shown.

Commentary by Dr. Valentin Fuster
2010;():437-448. doi:10.1115/GT2010-22067.

Pressure losses between compressor outlet and turbine inlet are a major issue of overall efficiency and system stability for a SOFC/MGT hybrid power plant system. The goal of this work is the detailed analysis of the effects of additional pressure losses on MGT performance in terms of steady-state and transient conditions. The experiments were performed at the micro gas turbine test rig at the German Aerospace Centre in Stuttgart using a butterfly control valve to apply additional pressure loss. The paper reports electric power and pressure characteristics at steady-state conditions, as well as, a new surge limit, which was found for the Turbec T100 micro gas turbine. Furthermore, the effects of additional pressure loss on compressor surge margin are quantified and a linear relation between relative surge margin and additional pressure loss is shown. For transient variation of pressure loss at constant turbine speed time delays are presented and a compensation issue of the commercial gas turbine controller is discussed. Finally, bleed-air blow-off and reduction of turbine outlet temperature are introduced as methods of increasing surge margin. It is quantified that both methods have a substantial effect on compressor surge margin. Furthermore, a comparison between both methods is given in terms of electric power output.

Commentary by Dr. Valentin Fuster
2010;():449-458. doi:10.1115/GT2010-22073.

Exergy analysis provides useful information about the system optimization. An exergy analysis identifies the sources of thermodynamic inefficiencies by evaluating the exergy destruction within each system component. Splitting the exergy destruction into endogenous/exogenous parts represents a new development in the exergy analysis of energy conversion systems. The present work is an attempt to investigate the combustion process in a simple gas turbine and a cogeneration power plant based on the general concept of endogenous and exogenous exergy destruction. Therefore, using a graphical approach, the advanced exergy analysis is applied to both cycles with different fuels such as methane and diesel. Also, dual-fueling of combustion chamber is investigated based on the aforementioned approach in which 90% substitution of methane fuel for diesel one is considered. It is found that, in both cycles the combustion chamber has the largest value of the endogenous exergy destruction. The exergetic efficiency of combustion chamber increases when methane fuel is substituted for diesel fuel. Therefore, cycles efficiencies have been enhanced when fuel is substituted for diesel one. The results obtained here may provide some useful information for the optimal design and performance improvement of these cycles.

Commentary by Dr. Valentin Fuster
2010;():459-464. doi:10.1115/GT2010-22102.

The gas turbine engine performance is greatly relied on its component performance characteristics. Generally, acquisition of component maps is not easy for engine purchasers because it is an intellectual property of gas turbine engine supplier. In the previous work, the maps were inversely generated from engine performance deck data. However this method is limited to obtain the realistic maps from the calculated performance deck data. Present work proposes a novel method to generate more realistic component maps from experimental performance test data. In order to demonstrate the proposed method, firstly the NI data acquisition device with the proposed LabVIEW on-condition monitoring program monitors and collects real-time performance data such as temperature, pressure, thrust, and fuel flow etc. from a micro turbojet engine of the test setup which is specially manufactured for this study. Real-time data obtained from the test results are used for inverse generation of the component maps after processing by some numerical schemes. Realistic component maps can then be generated from those processed data using the proposed extended scaling method at each rotational speed. Verification can be made through comparison between performance analysis results using the performance simulation program including the generated compressor map and on-condition monitoring performance data.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2010;():465-474. doi:10.1115/GT2010-22124.

Solar hybrid power plants are characterized by a combination of heat input both of high temperature solar heat and heat from combustion of gaseous or liquid fuel which enables to supply the electricity market according to its requirements and to utilize the limited and high grade natural resources economically. The SHCC® power plant concept integrates the high temperature solar heat into the gas turbine process and in addition — depending on the scheme of the process cycle — downstream into the steam cycle. The feed-in of solar heat into the gas turbine is carried out between compressor outlet and combustor inlet either by direct solar thermal heating of the pressurized air inside the receivers of the solar tower or by indirectly heating via interconnection of a heat transfer fluid. Thus, high shares of solar heat input referring to the total heat input of more than 60% in design point can be achieved. Besides low consumption of fossil fuels and high efficiency, the SHCC® concept is aimed for a permanent availability of the power plant capacity due to the possible substitution of solar heat by combustion heat during periods without sufficient solar irradiation. In consequence, no additional standby capacity is necessary. SHCC® can be conducted with today’s power plant and solar technology. One of the possible variants has already been demonstrated in the test field PSA in Spain using a small capacity gas turbine with location in the head of the solar tower for direct heating of the combustion air. However, the authors present and analyze also alternative concepts for power plants of higher capacity. Of course, the gas turbine needs a design which enables the external heating of the combustion air. Today only a few types of gas turbines are available for SHCC® demonstration. But these gas turbines were not designed for solar hybrid application at all. Thus, the autors present finally some reflections on gas turbine parameters and their consequences for SHCC® as basis for evaluation of potentials of SHCC® .

Commentary by Dr. Valentin Fuster
2010;():475-484. doi:10.1115/GT2010-22132.

New health monitoring strategies were developed in the last decade aiming at improvement of gas turbines safety and reliability. Real time methodologies have been considered of major concern for safe operation at least cost. This paper describes a hybrid system approach for turboshaft faults diagnosis, using data obtained from a tuned high fidelity gas turbine simulator program, including those for multiple faults deteriorated performance. Kohonen neural network was used to analyze similarity together with an optimization strategy to reduce the volume of data used in the diagnostics phase. A Multi-Layer Perceptron (MLP) was used for training and validation. The MLP and Kohonen networks were tested for several configurations, in order to improve diagnosis. The hybrid system was also tested with noise-contaminated data and it was verified the capability of the neural approach to detect and isolate multiple faults better than the MLP alone. The results showed that the optimization strategy reduced significantly the database patterns and improved the learning process, demonstrating high precision to diagnose gas turbine operation problems. The reliability of the proposed system is explained both qualitatively and quantitatively.

Commentary by Dr. Valentin Fuster
2010;():485-492. doi:10.1115/GT2010-22171.

Development of a closed cycle gas turbine using supercritical carbon dioxide as a working fluid is underway to generate power from industrial waste heat sources of a low or intermediate temperature range. Its demonstration test plan using a reduced scale turbomachine is described herein. Principal specifications include the following: net power output of 10 kWe and recirculation CO2 with flow rate of 1.2 kg/s under given turbine inlet conditions of 550 K and 12 MPa. The optimized ranges of compressor inlet temperatures and pressures are investigated in this study. Given these inlet conditions, primary and auxiliary component development is done. Coupled with cycle analysis, the design rotational speed of the co-axially aligned turbomachine was determined as 100,000 rpm. Aerodynamic CFD analyses were conducted for the centrifugal compressor considering real gas properties. Preliminary test results show indirect evidence of compressor work reduction inherent to the supercritical CO2 gas turbine concept.

Commentary by Dr. Valentin Fuster
2010;():493-503. doi:10.1115/GT2010-22189.

The IEA World Energy Outlook 2009 predicts a considerable growth of the world’s primary energy demand and states that fossil fuels will remain the dominant source of primary energy. Among them coal will increase its share because of its vast reserves, its relatively even global distribution and its low prices compared to oil and gas. On the other hand the burning of coal emits larger quantities of CO2 than oil and gas. As CO2 is the leading cause for global warming, the use of coal for power generation demands a clean coal technology with carbon capture and storage (CCS). Therefore in this work it is suggested to combine a coal gasification unit with a Graz Cycle power plant, an oxy-fuel technology of highest efficiency. The firing of the syngas from coal gasification with pure oxygen avoids the expensive pre-combustion CO2 sequestration and leads to a working fluid of CO2 and steam, where CO2 is captured by simple steam condensation. In contrast to this, the more conventional technology is to send the syngas to a water-shift reactor and a CO2 scrubber so that a fuel containing mainly hydrogen is obtained which can be fired in a conventional combined cycle plant. In order to evaluate these two competing technologies a thermodynamic simulation as well as an economic cost analysis of both power cycles is performed. It turns out that the achievable efficiency of the Graz Cycle plant is — despite of the increased oxygen demand — far higher than that of a plant of conventional capture technology due to the avoidance of shift reaction and scrubbing. The following economic analysis shows mitigation costs of 22.5 €/ton CO2 avoided for the Graz Cycle plant compared to 33 €/ton for an IGCC plant with CO2 capture.

Commentary by Dr. Valentin Fuster
2010;():505-512. doi:10.1115/GT2010-22192.

Naturally occurring limestone and samples from a lab scale dual fluidized bed (DFB) calcium looping (CaL) test facility were analysed in a thermo gravimetric analyser (TGA). The reactivity of the samples evaluated at typical carbonation conditions prevailed in the carbonator was compared with raw samples. Carbonations were carried out at 600, 650 &700°C and 5, 10 &15 vol-% CO2 atmosphere using a custom designed sample holder that provided ideal conditions for solid gas contact in a TGA. The rate of carbonation and carbonation capacity of the samples were compared with respect to the following three categories: number of calcination-carbonation cycles, carbonation temperature and CO2 concentration. Notable differences in total conversion (XCaO ) and the rates of conversions were observed between the raw and DFB samples in all three cases. It is suspected the much lower activity of the DFB sample is attributed to the differences in experimental conditions: ie., partial carbonation of the DFB particles, fast heating rate in the calciner and thus a rapid calcination reaction, and particle attrition in the CFB calciner riser. These harsh conditions lead sintering and thus a loss of surface area and reactivity. Sintered DFB samples showed low (nearly 1/3 of the raw samples) but stable conversions with increasing number of cycles. The sorbent taken from the DFB facility did not decrease with respect to carbonation rate or maximum conversion over 4 cycles whereas the fresh limestone changed significantly over 4 cycles. Hydration was used as an attempt to regenerate the lost capture capacity of partially carbonated DFB sample. Hydration of the sintered DFB sample was successful in increasing the maximum capture capacity in the fast reaction regime to values almost as high as that of a fresh sample in its first carbonation cycle. Although more investigation is required to investigate the effect of hydration on the CaO particle morphology, a process modification to enhance the CO2 capture efficiency of the carbonator via particle hydration was proposed.

Commentary by Dr. Valentin Fuster
2010;():513-520. doi:10.1115/GT2010-22282.

This proposal fully complies to the demands of a zero emission power plant since only hydrogen and oxygen as obtained from splitting water are provided as fuel in a working gas cycle of pure water. Distributed power plants based on solar radiation, solar heat, wind power and water power from river flow, tidal flow and even wave motion should drive electrolysers producing hydrogen and oxygen. The units are connected with a pipeline system delivering hydrogen and oxygen at high pressure into respective storage tanks in the vicinity of the proposed power plant. So periods of generation of hydrogen and oxygen can overlap and these fuel gases are available to produce peak power according to demand. The proposed plant is an hybrid plant incorporating SOFC fuel cells into an innovative power cycle with steam as working fluid. Twelve fuel cells of 2.5 MW power produce electricity and heat up working fluid from 600 to 800°C. In a succeeding combustion chamber the fuel cell surplus hydrogen as well as the gas turbine hydrogen demand is burned with pure oxygen leading to a working gas (steam) of 1550°C and 40 bar. The working gas is expanded in an innovative cycle producing additional 109 MW of electrical energy. So an overall output of 139 MW can be achieved with a thermal efficiency of 73.8% based on fuel taken from the storage tanks for hydrogen and oxygen at 60 bar.

Commentary by Dr. Valentin Fuster
2010;():521-532. doi:10.1115/GT2010-22285.

Accurate gas turbine performance models are crucial in many gas turbine performance analysis and gas path diagnostic applications. With current thermodynamic performance modelling techniques, the accuracy of gas turbine performance models at off-design conditions is determined by engine component characteristic maps obtained in rig tests and these maps may not be available to gas turbine users or may not be accurate for individual engines. In this paper, a non-linear multiple point performance adaptation approach using a Genetic Algorithm is introduced with the aim to improve the performance prediction accuracy of gas turbine engines at different off-design conditions by calibrating the engine performance models against available test data. Such calibration is carried out with introduced non-linear map scaling factor functions by ‘modifying’ initially implemented component characteristic maps in the gas turbine thermodynamic performance models. A Genetic Algorithm is used to search for an optimal set of non-linear scaling factor functions for the maps via an objective function that measures the difference between the simulated and actual gas path measurements. The developed off-design performance adaptation approach has been applied to a model single spool turboshaft aero gas turbine engine and demonstrated a significant improvement in the performance model accuracy at off-design operating conditions.

Commentary by Dr. Valentin Fuster
2010;():533-545. doi:10.1115/GT2010-22332.

A thorough assessment of component life is very important to ensure both the safety and economics of gas turbine operation. As a component’s life given by OEM is based on certain ambient and operating conditions, its actual life may vary substantially when the ambient, operating and engine health conditions change. Therefore possessing knowledge on how those conditions affect actual component life will be valuable in making informed maintenance decisions, maximising operation effectiveness and cutting down operating costs. In this paper, an impact analysis on component creep life due to different operating and engine health conditions using an introduced Creep Factor is performed, which aims to provide useful insights on the relationship between gas turbine performance change and hot section component’s creep life. As the Creep Factor is defined as the ratio between the actual creep life and a reference creep life at a user-defined condition, the magnitude of the impact can be quantified with the change of the Creep Factor. The developed creep life analysis approach was applied to a model single spool turboshaft gas turbine engine operated at various operating and health conditions. A physics-based model combined with the Creep Factor approach was then used to estimate the creep life variation of the high pressure turbine of the model engine. The results showed that for a clean engine, the change in the rotational speed has given the highest impact on the creep life consumption. Also the presence of blade cooling and component degradation is seen to significantly reduce the blade’s creep life and as the degradation effects are combined, the degree of reduction increases even more. It also shows that the Creep Factor is good indicator of creep life consumption and provides a good technique to rank the influencing factor according to the threat they imposed.

Topics: Creep , Gas turbines
Commentary by Dr. Valentin Fuster
2010;():547-558. doi:10.1115/GT2010-22334.

This paper investigates the relationship between design parameters and creep life consumption of stationary gas turbines using a physics based life model. A representative thermodynamic performance model is used to simulate engine performance. The output from the performance model is used as an input to the physics based model. The model consists of blade sizing model which sizes the HPT blade using the constant nozzle method, mechanical stress model which performs the stress analysis, thermal model which performs thermal analysis by considering the radial distribution of gas temperature, and creep model which using the Larson-miller parameter to calculate the lowest blade creep life. The effect of different parameters including radial temperature distortion factor (RTDF), material properties, cooling effectiveness and turbine entry temperatures (TET) is investigated. The results show that different design parameter combined with a change in operating conditions can significantly affect the creep life of the HPT blade and the location along the span of the blade where the failure could occur. Using lower RTDF the lowest creep life is located at the lower section of the span, whereas at higher RTDF the lowest creep life is located at the upper side of the span. It also shows that at different cooling effectiveness and TET for both materials the lowest blade creep life is located between the mid and the tip of the span. The physics based model was found to be simple and useful tool to investigate the impact of the above parameters on creep life.

Topics: Creep , Design , Gas turbines
Commentary by Dr. Valentin Fuster
2010;():559-568. doi:10.1115/GT2010-22389.

This article illustrates aspects of heat recovery steam generator (HRSG) design when employing process integration in an integrated reforming combined cycle (IRCC) with pre-combustion CO2 capture. Specifically, the contribution of the paper is to show how heat integration in a pre-combustion CO2 capture plant impacts the selection of HRSG design. The purpose of such a plant is to generate power with very low CO2 emissions, typically below 100 g CO2 /net kWh electricity. This should be compared to a state-of-the-art natural gas combined cycle (NGCC) plant with CO2 emissions around 380 g CO2 /net kWh electricity. The design of the HRSG for the IRCC process was far from standard because of the significant amount of steam production from the heat generated by the auto-thermal reforming process. This externally generated steam was transferred to the HRSG superheaters and used in a steam turbine. For an NGCC plant, a triple-pressure reheat steam cycle would yield the highest net plant efficiency. However, when generating a significant amount of high-pressure steam external to the HRSG, the picture changed. The complexity of selecting a HRSG design increased when also considering that steam can be superheated, and low-pressure and intermediate-pressure steam can be generated in the process heat exchangers. For the concepts studied it was also of importance to maintain a high net plant efficiency when operating on natural gas. Therefore the selection of HRSG design had to be a compromise between NGCC and IRCC operating modes.

Commentary by Dr. Valentin Fuster
2010;():569-579. doi:10.1115/GT2010-22402.

Gas path analysis (GPA) is a powerful tool to predict gas turbine degradations based on measurement parameters of gas turbine engines. Accordingly, prudent measurement selections are crucial to ensure accurate GPA predictions. This paper is intended to investigate the influence of measurement parameter selection towards the effectiveness of GPA algorithm. An analytical methodology for measurement selection, combined with measurement subset concept, is developed to properly select measurements for multiple component fault diagnosis. The effectiveness of GPA using the measurement sets selected with the introduced measurement selection method are then compared to the results of using standard measurements installed on existing gas turbine engines. A case study applying the new measurement selection method to GPA diagnostic analysis is demonstrated on a 3-shaft aero-derivative industrial gas turbine model based on similar unit installed onboard an offshore platform operated by PETRONAS. The engine is modeled and simulated using PYTHIA, a gas turbine performance and diagnostics analysis tool developed by Cranfield University. To validate the findings, non-linear GPA prediction errors are evaluated in various cases of single and multi components faults. As a result, the selected measurements have successfully produced much superior diagnostics accuracies in the fault cases when compared to the standard measurements. These findings proved that proper measurement selection for better GPA diagnostic analysis can be achieved by using the proposed analytical methods. Several engine sensor enhancements are also discussed to accommodate the unique sensor requirements for health diagnostics using GPA.

Commentary by Dr. Valentin Fuster
2010;():581-593. doi:10.1115/GT2010-22413.

The external recirculation of exhaust gases represents an effective tool for approaching an almost flameless regime and controlling the nitric oxide formation, like demonstrated by a number of authors’ papers. Such a system penalizes, on the other hand, the micro-gas turbine performance due to the high EGR rates that are needed for the pollutant reduction. Basing on this consideration, the author consider, in this paper, the possibility of exploiting the internal combustion fluid-dynamics for achieving the same level of pollutant abatement. The comparison of the combustion regimes that are induced by either the external or internal EGR adoption are carried out on a CFD basis. The results refer to different load conditions of the micro-gas turbine, with both gaseous and liquid fuel supply.

Commentary by Dr. Valentin Fuster
2010;():595-607. doi:10.1115/GT2010-22420.

This paper presents an evolutionary approach as the optimization framework to design for the optimal performance of a high-bypass unmixed turbofan to match with the power requirements of a commercial aircraft. The parametric analysis had the objective to highlight the effects of the principal design parameters on the propulsive performance in terms of specific fuel consumption and specific thrust. The design optimization procedure based on the genetic algorithm PIKAIA coupled to the developed engine performance analyzer (on-design and off-design) aimed at finding the propulsion cycle parameters minimizing the specific fuel consumption, while meeting the required thrusts in cruise and takeoff and the restrictions of temperatures limits, engine size and weight as well as pollutants emissions. This methodology does not use engine components’ maps and operates on simplifying assumptions which are satisfying the conceptual or early design stages. The predefined requirements and design constraints have resulted in an engine with high mass flow rate, bypass ratio and overall pressure ratio and a moderate turbine inlet temperature. In general, the optimized engine is fairly comparable with available engines of equivalent power range.

Commentary by Dr. Valentin Fuster
2010;():609-620. doi:10.1115/GT2010-22470.

This paper compares and demonstrates the efficacy of implementing two practical Single Input Single Output (SISO) multi-loop control schemes on the dynamic performance of selected signals of a Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) hybrid simulation facility. The hybrid plant, located at the U.S. Department of Energy National Energy Technology Laboratory (NETL) in Morgantown WV, is capable of simulating the interaction between a 350kW SOFC and a 120kW GT using a Hardware-in-the-Loop (HIL) configuration. Previous studies have shown that the thermal management of coal based SOFC-GT hybrid systems is accomplished by the careful control of the cathode air stream within the fuel cell (FC). A decoupled centralized and dynamic de-centralized control scheme is tested for one critical airflow bypass loop to regulate cathode FC airflow and modulation of turbine electric load to maintain synchronous turbine speed during system transients. Improvements to the studied multivariate architectures include: feed-forward (FF) control for disturbance rejection, anti-windup (AW) compensation for actuator saturation, gain scheduling for adaptive operation, bumpless transfer (BT) for manual to auto switching, and adequate filter design for the inclusion of derivative action. Controller gain tuning is accomplished by Skogestad’s Internal Model Control (SIMC) tuning rules derived from empirical First Order Plus Delay Time (FOPDT) Transfer Function {TF} models of the hybrid facility. Avoidance of strong Input-Output (IO) coupling interactions is achieved via Relative Gain Array (RGA), Niederlinski Index (NI), and Decomposed Relative Interaction Analysis (DRIA), following recent methodologies in PID control theory for multivariable processes.

Commentary by Dr. Valentin Fuster
2010;():621-626. doi:10.1115/GT2010-22518.

Unsteady, non-isentropic, discontinuous flows with energy exchange, during solar heating transients of air turbine towers are approached through a proprietary computational front method, initially developed for the study of ignition in solid propellant rocket motors. Its application in the discontinuous flows with energy exchange also proves highly efficient. Computational efficiency is demonstrated by CFD simulation of transients in the air accelerator of the SEATTLER solar mirror, turbine tower. This is a typically unsteady flow simulation for slender channels. A 1-D computational scheme was developed to simulate the interference between zones with different flow conditions. Given values for the thermochemical properties of the working gas are considered and two zones of different flow characteristics are identified. The first zone is the heat exchanger, where a nonisentropic flow develops. At the aft end of this heating zone a second zone of the channel is encountered after a blunt passage, where an isentropic expansion of the gas begins and extends along the tower up to the upper exit. Into the 1-D, unsteady flow scheme of computation, the discontinuity of equations of motion at the interface between the two zones induces very specific precautions and this methodology is detailed into the paper. Consequently, the computational front scheme covers the dual behavior of the fully non-isentropic flow with mass addition and mixing in the heater and of the fully isentropic flow at the exhaust of the gravity draught tall tower, typical for the solar-gravity draught power plants. Small perturbations of the flow, in the form of developing weak shocks, and blunt discontinuities are simultaneously covered. Code robustness is demonstrated and revealed through diagrams. The 1-D numerical scheme is based on the enhanced method of the computational front with resolution of the expansion wave development.

Commentary by Dr. Valentin Fuster
2010;():627-633. doi:10.1115/GT2010-22519.

The performance of an intercooled turbofan engine is analysed by multidisciplinary optimization. A model for making preliminary simplified analysis of the mechanical design of the engine is coupled to an aircraft model and an engine performance model. A conventional turbofan engine with technology representative for a year 2020 entry of service engine is compared to a corresponding intercooled engine. A mission fuel burn reduction of 4.3% is observed. The results are analysed in terms of the relevant constraints such as compressor exit temperature, turbine entry temperature, turbine rotor blade temperature and compressor exit blade height. It is then shown that a separate variable exhaust nozzle mounted in conjunction with the intercooler together with a variable low pressure turbine may further improve the fuel burn benefit to 5.5%. Empirical data and a parametric CFD study is used to verify the intercooler heat transfer and pressure loss characteristics.

Topics: Engines , Turbofans
Commentary by Dr. Valentin Fuster
2010;():635-641. doi:10.1115/GT2010-22537.

The helicopter to be operated in a severe flight environmental condition must have a very reliable propulsion system. On-line condition monitoring and fault detection of the engine can promote reliability and availability of the helicopter propulsion system. A hybrid health monitoring program using Fuzzy Logic and Neural Network Algorithms is can proposed. In this hybrid method, the Fuzzy Logic identify easily the faulted components from engine measuring parameter changes, and the Neural Networks can quantify accurately its identified faults. In order to use effectively the fault diagnostic system, a GUI (Graphical User Interface) type program is newly proposed. This program is composed of the real time monitoring part, the engine condition monitoring part and the fault diagnostic part. The real time monitoring part can display measuring parameters of the study turboshaft engine such as power turbine inlet temperature, exhaust gas temperature, fuel flow, torque and gas generator speed. The engine condition monitoring part can evaluate the engine condition through comparison between monitoring performance parameters the base performance parameters analyzed by the base performance analysis program using look-up tables. The fault diagnostic part can identify and quantify the single faults the multiple faults from the monitoring parameters using hybrid method.

Commentary by Dr. Valentin Fuster
2010;():643-651. doi:10.1115/GT2010-22701.

A novel engine concept, for reducing the environmental impact of gas turbines, is the Geared Turbofan with Active Core technologies (GTAC), investigated in the context of the European program NEWAC (New Aero Engine Core Concepts). Two performance models of this engine are created for short and long range aircraft applications and matched to manufacturer specifications. The engine performance data are used in a mission analysis module simulating typical aircraft applications. Compared to missions using Year 2000 in service engines, the results show a significant reduction in fuel consumption and noise levels. A significant reduction in NOx emissions requires the application of new technology combustor designs as developed e.g. in NEWAC.

Topics: Turbofans
Commentary by Dr. Valentin Fuster
2010;():653-660. doi:10.1115/GT2010-22734.

This paper presents performance analysis of a hybrid power generation system consisting of a solid oxide fuel cell (SOFC) and a steam injected gas turbine (GT) based on the commercial software Easy5. The steam is produced by using the hot exhaust gases heat in the heat recovery steam generator (HRSG) and is injected into the afterburner. Compared with the system without HRSG, the exhaust gas temperature decreases slightly and the power output of the gas turbine is higher because of the increase of the inlet mass flow rate. In addition, the heat exchanger reformer is used in the hybrid system to reduce space and cost. Simulation results show that the hybrid system could achieve a system efficiency of 62.6% under full load operation. And the part load and the dynamic performance of the hybrid system was presented and analyzed.

Commentary by Dr. Valentin Fuster
2010;():661-670. doi:10.1115/GT2010-22752.

This paper deals with the thermodynamic analysis of an IGCC power plant with hot syngas clean-up, where sulfur, particulate matter and trace contaminants are removed without cooling the syngas down to near-ambient temperature. With particular attention to the simulation of the desulfurization unit, adopting a regenerative process using a ZnO-based sorbent, a range of clean-up temperatures was investigated in order to evaluate its effects on overall plant performance. The study reveals the attractive chance of achieving overall electric efficiencies around 50%. However, a limited sensitivity of IGCC efficiency on desulfurization temperature was also obtained, since no significant improvements were accomplished for temperatures over 400°C. In order to support and better understand the results, a second law analysis was also carried out for the assessed cases. In addition, the effects of syngas clean-up temperature on the design and operation of the main IGCC processes and components, which can be relevant, were discussed.

Topics: Temperature , Syngas
Commentary by Dr. Valentin Fuster
2010;():671-681. doi:10.1115/GT2010-22799.

For the development of efficient and fuel flexible decentralized power plant concepts a test rig based on the Turbec T100 micro gas turbine is operated at the DLR Institute of Combustion Technology. This paper reports the characterization of the transient operating performance of the micro gas turbine by selected transient maneuvers like start-up, load change and shut-down. The transient maneuvers can be affected by specifying either the electrical power output or the turbine speed. The impact of the two different operation strategies on the behavior of the engine is explained. At selected stationary load points the performance of the gas turbine components is characterized by using the measured thermodynamic and fluid dynamic quantities. In addition the impact of different turbine outlet temperatures on the performance of the gas turbine is worked out. The resulting data set can be used for validation of numerical simulation and as a base for further investigations on micro gas turbines.

Commentary by Dr. Valentin Fuster
2010;():683-693. doi:10.1115/GT2010-22814.

Application of Solid Oxide Fuel Cells (SOFC) in gasification-based power plants would represent a turning point in the power generation sector, allowing to considerably increase the electric efficiency of coal-fired power stations. Pollutant emissions would also be significantly reduced in Integrated Gasification Fuel Cell cycles (IGFC) considering the much lower emissions of conventional pollutants (NOx , CO, SOx , particulate matter) typical of fuel cell-based systems. In addition, SOFC-based IGFCs appear particularly suited to applications in power plants with CO2 capture. This is evident by considering that SOFCs operate as air separators and partly oxidized fuel exiting the fuel cell does not contain nitrogen from air, like in conventional oxy-fuel processes. The aim of the present paper is the thermodynamic analysis of a SOFC-based IGFC with CO2 capture. In the assessed plant, syngas produced in a high efficiency Shell gasifier is used in SOFC modules after heat recovery and cleaning. Anode exhausts, still containing combustible species, are burned with oxygen produced in the air separation unit, also used to generate the oxygen needed in the gasifier; the product gas is cooled down in a heat recovery steam generator before water condensation and CO2 compression. The plant layout is carefully designed to best exploit heat generated in all the processes and, apart from the fuel cell, exotic components, far from industrial state-of-the-art, are not included. Detailed energy and mass balances are presented for a better comprehension of the obtained results.

Commentary by Dr. Valentin Fuster
2010;():695-701. doi:10.1115/GT2010-22862.

Recently, modeling and simulation (M&S) has been used to predict the performance of a system in its operating conditions in order to reduce the cost and period of a development. Due to this reason, the necessity of modeling and simulation has been rapidly increased in system developments. A modeling and simulation program for an environmental control system (ECS) of a pod installed under wings of an aircraft was developed in order to estimate the system’s performance during the vehicle flight. First, through the system configuration analysis in the main operational condition of the aircraft system, an ECS configuration adopting an air cycle machine (ACM) was selected. Therefore the modeling program was developed to simulate the ECS with an ACM. Second, the sensitivity analyses on performance variation of main components were conducted to complete the conceptual design of the ECS. A design point for the system and its components was obtained through the analysis with the modeling and simulation program. Third, in order to study the feasibility of the ECS configuration, off-design performances of the ECS on various flight conditions, such as take off, manoeuvre, cruise and landing etc were estimated. Dynamic characteristics were analyzed by transient performance evaluations. From results of this study, overall performances of the ECS were able to be estimated and predicted prior to manufacturing an actual ECS with the modeling and simulation program so that development costs and oversights could be minimized. Moreover an optimum design process has been established for the ECS in this study.

Commentary by Dr. Valentin Fuster
2010;():703-710. doi:10.1115/GT2010-22867.

This work presents the performance study of a 1 MW gas turbine including the effects of blade cooling and compressor variable geometry. The axial flow compressor, with Variable Inlet Guide Vane (VIGV), was designed for this application and its performance maps synthesized using own high technological contents computer programs. The performance study was performed using a specially developed computer program, which is able to numerically simulate gas turbine engines performance with high confidence, in all possible operating conditions. The effects of turbine blades cooling were calculated for different turbine inlet temperatures (TIT) and the influence of the amount of compressor-bled cooling air was studied, aiming at efficiency maximization, for a specified blade life and cooling technology. Details of compressor maps generation, cycle analysis and blade cooling are discussed.

Commentary by Dr. Valentin Fuster
2010;():711-719. doi:10.1115/GT2010-22886.

In this paper, a performance assessment of integrated solar combined cycle systems (ISCCS) is reported on. The main aim of the study was to evaluate the solar conversion efficiency of ISCCS plants based on parabolic troughs using CO2 as heat transfer fluid. The use of CO2 instead of the more conventional thermal oil as heat transfer fluid can allow an increase in the trough outlet temperature and thus in solar energy conversion efficiency. In particular, the ISCCS plant considered here was developed on the basis of a triple-pressure, reheated combined cycle power plant rated at 252 MW. Two different solutions for the solar steam generator are considered and compared. Moreover, the performance of the ISCCS system was evaluated with reference to different values of CO2 maximum temperature, solar radiation and solar share of the power output. The results of the performance assessment show that the solar energy conversion efficiency ranges from 23% to 25% for a CO2 maximum temperature of 550°C. The use of a CO2 temperature of 450°C reduces the solar efficiency by about 1.5–2.0 percentage points. The use of a solar steam generator including only the evaporation section instead of the preheating, evaporation and superheating sections allows the achievement of slightly better conversion efficiencies. However, the adoption of this solution leads to a maximum value of the solar share around 10% on the ISCCS power output. The solar conversion efficiencies of the ISCCS systems considered here are better than those of the more conventional Concentrating Solar Power (CSP) systems based on steam cycles (14–18%) and are very similar to the predicted conversion efficiencies of the more advanced direct steam generation plants (22–27%).

Commentary by Dr. Valentin Fuster
2010;():721-731. doi:10.1115/GT2010-22996.

The first steps of the turbomachinery design usually rely on numerical tools based on inviscid formulation with corrections using loss models to account for viscous effects, secondary flows, tip clearances and shock waves. The viscous effects are accounted for using semi-empirical correlations specially assembled for the chosen airfoils and range of operating conditions. Fast convergence and good accuracy are required from such design procedures. There are successful models that produce very accurate performance prediction. Among the methodologies commonly used, the streamline curvature (SLC) is used, since those characteristics and the most important properties can be calculated reasonably well at any radial positions, assisting other more complex analysis programs. The SLC technique is, therefore, well suited for the design of axial flow compressors, for reasons like quick access to vital flow properties at the blade edges, from which actions may be taken to improve its performance at the design stage. This work reports the association of a SLC computer program and commercial software for comparison purposes, as well as for grid generation required by a full 3D, turbulent Navier-Stokes computer program, used for flow calculation in the blade passages. Application to a high performance 3-stage axial-flow compressor with Inlet Guide Vane (IGV) demonstrates the methodology adopted. The SLC program is also capable of calculating the compressor performance with humid air and water injection at any axial position along the compressor. The influence of water injection at different axial positions, water particle diameter, temperature of water particles were studied for different humid air conditions. The positions of the evaporating water particles were calculated using their thermo-physical and dynamic properties along the compressor.

Commentary by Dr. Valentin Fuster
2010;():733-743. doi:10.1115/GT2010-23001.

Future fossil-fueled power generation systems will require carbon capture and sequestration to comply with government green house gas regulations. The three prime candidate technologies that capture carbon dioxide (CO2 ) are pre-combustion, post-combustion and oxy-fuel combustion techniques. Clean Energy Systems, Inc. (CES) has recently demonstrated oxy-fuel technology applicable to gas turbines, gas generators, and reheat combustors at their 50MWth research test facility located near Bakersfield, California. CES, in conjunction with Siemens Energy, Inc. and Florida Turbine Technologies, Inc. (FTT) have been working to develop and demonstrate turbomachinery systems that accommodate the inherent characteristics of oxy-fuel (O-F) working fluids. The team adopted an aggressive, but economical development approach to advance turbine technology towards early product realization; goals include incremental advances in power plant output and efficiency while minimizing capital costs and cost of electricity [1]. Proof-of-concept testing was completed via a 20MWth oxy-fuel combustor at CES’s Kimberlina prototype power plant. Operability and performance limits were explored by burning a variety of fuels, including natural gas and (simulated) synthesis gas, over a wide range of conditions to generate a steam/CO2 working fluid that was used to drive a turbo-generator. Successful demonstration led to the development of first generation zero-emission power plants (ZEPP). Fabrication and preliminary testing of 1st generation ZEPP equipment has been completed at Kimberlina power plant (KPP) including two main system components, a large combustor (170MWth ) and a modified aeroderivative turbine (GE J79 turbine). Also, a reheat combustion system is being designed to improve plant efficiency. This will incorporate the combustion cans from the J79 engine, modified to accept the system’s steam/CO2 working fluid. A single-can reheat combustor has been designed and tested to verify the viability and performance of an O-F reheater can. After several successful tests of the 1st generation equipment, development started on 2nd generation power plant systems. In this program, a Siemens SGT-900 gas turbine engine will be modified and utilized in a 200MWe power plant. Like the 1st generation system, the expander section of the engine will be used as an advanced intermediate pressure turbine and the can-annular combustor will be modified into a O-F reheat combustor. Design studies are being performed to define the modifications necessary to adapt the hardware to the thermal and structural demands of a steam/CO2 drive gas including testing to characterize the materials behavior when exposed to the deleterious working environment. The results and challenges of 1st and 2nd generation oxy-fuel power plant system development are presented.

Commentary by Dr. Valentin Fuster
2010;():745-752. doi:10.1115/GT2010-23026.

A gas-turbine cogeneration system with a regenerative air preheater and a single-pressure exhaust gas boiler serves as an example for application of CHP Plant. This CHP plant which can provide 30 MW of electric power and 14kg/s saturated steam at 20 bars. The plant is comprised of a gas turbine, air compressor, combustion chamber, and air pre-heater as well as a heat recovery steam generator (HRSG). The design Parameters of the plant, were chosen as: compressor pressure ratio (rc ), compressor isentropic efficiency (ηac ), gas turbine isentropic efficiency (ηgt ), combustion chamber inlet temperature (T3 ), and turbine inlet temperature (T4 ). In order to optimally find the design parameters a thermoeconomic approach has been followed. An objective function, representing the total cost of the plant in terms of dollar per second, was defined as the sum of the operating cost, related to the fuel consumption. Subsequently, different pars of objective function have been expressed in terms of decision variables. Finally, the optimal values of decision variables were obtained by minimizing the objective function using Evolutionary algorithm such as Genetic Algorithm. The influence of changes in the demanded power on the design parameters has been also studied for 30, 40 MW of net power output.

Commentary by Dr. Valentin Fuster
2010;():753-758. doi:10.1115/GT2010-23124.

The high-temperature gas-cooled reactor (HTGR) technology is the only nuclear technology capable of achieving coolant temperatures as high as 950 °C and at the same time ensuring safe and efficient production of electricity, process steam and hydrogen. HTGR can be combined with a gas turbine to be gas turbine cycle with HTGR. This cycle can make use of high temperature (750–950°C) gas heated by HTGR to generate electricity with high efficiency. Because it breaks through the temperature limit of steam cycle and incorporates the inter-cooling and recuperating, so the gas turbine cycle with HTGR is expected to be a competing candidate for future concepts of high efficiency power generation. The performance of direct gas turbine with HTGR coupled with recuperating, inter-cooling and pre-cooling process was investigated. Considering the selection of working fluid, the thermal efficiency of gas turbine with HTGR with helium, nitrogen, carbon dioxide and their mixtures as the working fluid was compared. Then, the influence of different parameters such as turbine inlet temperature, pressure loss coefficient and recuperation effectiveness on cycle efficiency was analyzed. Some useful conclusions were drawn on the system performance.

Commentary by Dr. Valentin Fuster
2010;():759-768. doi:10.1115/GT2010-23198.

This paper explains a performance simulation program for power generation gas turbines and its application to an IGCC gas turbine. The program has a modular structure and both the stage-level and entire component-level models were adopted. Stage-by-stage calculations were used in the compressor and the turbine. In particular, the compressor module is based on a stage-stacking method and is capable of simulating the effect of variable stator vanes. The combustor model has the capability of dealing with various fuels including syngas. The turbine module is capable of estimating blade cooling performance. The program can be easily extended to other applied cycles such as recuperated and reheated cycles because the program structure is fully modular. The program was verified for simple cycle commercial engines. In addition, the program was applied to the gas turbine in an IGCC plant. Influences of major system integration parameters on the operating conditions of the compressor and turbine as well as on engine performance were analyzed.

Commentary by Dr. Valentin Fuster
2010;():769-779. doi:10.1115/GT2010-23199.

In this paper, a novel multi-functional energy system (MES) fueled by natural gas and solar radiation is proposed. In this MES, hydrogen and electricity are co-generated and approximately 92% of CO2 derived from natural gas is removed. The solar concentrated process provides high-temperature thermal energy to the methane/steam reforming reaction. The resulting syngas enters a pressure swing adsorption unit to separate approximately 80% of hydrogen. This process significantly increases the concentration of carbon dioxide in syngas from nearly 19% to 49%, which decreases energy consumption in CO2 removal. As a result, the overall efficiency of the new system becomes about 61.1%. Compared to a conventional natural gas-based hydrogen plant with CO2 removal and a concentrated solar power tower plant, the overall efficiency of the new system is increased by 13.3 percentage points. Based on the graphical exergy analysis, the integration of synthetic utilization of natural gas and solar radiation, combination of the hydrogen production plant and power plant, and integration of the energy utilization processes and CO2 separation were found to play significant roles for the improvement of system performance. The result obtained here provides a new approach for CO2 removal with ultra-low thermal efficiency reduction (energy penalty) and high efficient use of solar radiation.

Commentary by Dr. Valentin Fuster
2010;():781-792. doi:10.1115/GT2010-23248.

The lower fuel burn and pollutant emissions of hybrid electric vehicles give a strong motivation and encourage further investigations in this field. The know how on hybrid vehicle technology is maturing and the reliability of such power schemes is being tested in the mass production. The current research effort is to investigate novel configurations, which could achieve further performance benefits. This paper presents, an assessment of a novel hybrid configuration comprising a micro gas turbine, a battery bank and a traction motor, focusing on its potential contribution to the reduction of fuel burn and emissions. The power required for the propulsion of the vehicle is provided by the electric motor. The electric power is stored by the batteries, which are charged by a periodic function of the micro gas turbine. The micro gas turbine starts up when the battery depth of discharge exceeds 80% and its function continues until the batteries are full. The performance of the vehicle is investigated using an integrated software platform. The calculated acceleration performance and fuel economy are compared to the ones of conventional vehicles of the same power. The sensitivity of the results to the variation of the vehicle parameters such as mass, kinetic energy recovery and battery type is calculated to identify the conditions under which the application of this hybrid technology offers potential benefits. The results indicate that if no mass penalties are incurred by the installation of additional components the fuel savings can exceed 23%. However, an increase in the vehicle’s weight can shrink this benefit, especially in the case of light vehicles. Lightweight batteries and kinetic energy recovery systems are deemed essential enabling technologies for a realistic application of this hybrid system.

Commentary by Dr. Valentin Fuster
2010;():793-802. doi:10.1115/GT2010-23253.

In computational engineering design the robust analysis comprises a prerequisite towards the successful development of future gas turbines. However, reliable determination of the statistical characteristics of variation of the operating conditions in a turbomachine is crucial. Initially, the variability of the physical operating conditions along the operating line on the compressor map is developed with the assistance of a through flow analysis tool. The probability density functions of the variability of the pressure profiles, mass flow, input angles, etc. of each individual stage of the compressor can be extracted and processed accordingly for 3D aerodynamic shape robust design. In this way, flexibility in detailed design is developed leading to innovative and creative thinking in modern turbomachinery design, but at the same time the intelligence and level of robust design is improved, and hence the quality of the designed product. For a particular compression system of a turbo-shaft engine all the details can be extracted, along the whole operating line, covering all the possible scenarios of individual operating conditions of each component. With this methodology the appropriate information is developed for robust analysis at the preliminary or detailed design phases of a compression system.

Commentary by Dr. Valentin Fuster
2010;():803-811. doi:10.1115/GT2010-23259.

The European electric power industry has undergone considerable changes over the past two decades as a result of more stringent laws concerning environmental protection along with the deregulation and liberalization of the electric power market. However, the pressure to deliver solutions in regard to the issue of climate change has increased dramatically in the last few years and given the rise to the possibility that future natural gas-fired combined cycle (NGCC) plants will also be subject to CO2 capture requirements. At the same time, the interest in combined cycles with their high efficiency, low capital costs and complexity has grown as a consequence of addressing new challenges posed by the need to operate according to market demand in order to be economically viable. Considering that these challenges will also be imposed on new natural gas-fired power plants in the foreseeable future, this study presents a new process concept for natural gas combined cycle power plants with CO2 capture. The simulation tool IPSEpro is used to model a 400 MW single-pressure NGCC with post-combustion CO2 capture, using an amine-based absorption process with Monoethanolamine. To improve the costs of capture the gas turbine, GE 109FB, is utilizing exhaust gas recirculation, thereby increasing the CO2 content in the gas turbine working fluid to almost double that of conventional operating gas turbines. In addition, the concept advantageously uses approximately 20% less steam for solvent regeneration by utilizing preheated water extracted from HRSG. The further recovery of heat from exhaust gases for water preheating by use of an increased economizer flow results in an outlet stack temperature comparable to those achieved in combined cycle plants with multiple pressure levels. As a result, overall power plant efficiency as high as that achieved for a triple-pressure reheated NGCC with corresponding CO2 removal facility is attained. The concept thus provides a more cost-efficient option to triple-pressure combined cycles since the number of heat exchangers, boilers, etc. is reduced considerably.

Commentary by Dr. Valentin Fuster
2010;():813-820. doi:10.1115/GT2010-23298.

The shaft failure of a gas turbine engine can be considered as a potentially hazardous event. Since the turbine rotor becomes suddenly decoupled from the compressor, it will rapidly accelerate and disc bursting or blade shedding may be possible outcomes. Blade tangling occurring between the turbine blades and the downstream NGV stator vanes can be an effective mean to prevent dangerous over-speed conditions. Since experimental test arrangements are considered to be time and cost in-effective, impact simulations can aid the understanding of the main phenomena involved in the event and help the designer in reducing the possibility of dangerous over-speed conditions. This paper represents a first attempt to model the impact between turbines following a shaft failure event. The contribution of this paper is the modeling approach of turbines in contact after a shaft failure. The results of the impact simulation in terms of rotational speed, frictional torque and frictional energy are presented, while some basic checks of the FEA model are carried out to assess the plausibility of the derived results.

Commentary by Dr. Valentin Fuster
2010;():821-829. doi:10.1115/GT2010-23338.

This work presents the re-engineering of the TRANSAT 1.0 code which was developed to perform off-design and transient condition analysis of Saturators and Direct Contact Heat Exchangers. This model, now available in the 2.0 release, was originally implemented in FORTRAN language, has been updated to C language, fully coded into MATLAB/Simulink® environment and validated using the extensive set of data available from the MOSAT project, carried out by the Thermochemical Power Group of the University of Genoa. The rig consists of a fully instrumented modular vertical saturator, which is controlled and monitored with a LABVIEW® computer interface. The simulation software showed fair stability in computation and in response to step variation of the main parameters driving the thermodynamic evolution of the air and water flows. Considering the actual mass flow rates, a geometric similitude was used to avoid calculation instability due to flows under 100 g/s. Overall the model proved to be reliable and accurate enough for energy system simulations.

Commentary by Dr. Valentin Fuster
2010;():831-842. doi:10.1115/GT2010-23357.

The penetration of a jet of fluid into a traversal moving stream is a basic configuration of a wide range of engineering applications, such as film cooling and V/STOL aircrafts. This investigation examines experimentally the effect of blowing ratio of fans in cross flow, and numerically, the effect of the swirl velocity of jets in cross flow, downstream of the injection hole. The experimental results indicated an agreement with typically straight jets in cross flow (no vorticity), illustrating that the trace of the jet, remains close to the wall and subsequently enhance cooling at low blowing ratios in the case of turbine blade applications. However, the rotation of the jet results in an imparity between the two parts of the counter rotating vortex pair (CVP), and as a consequence, the injected fluid not only bends in the direction of the main stream but also diverts in the direction of the rotation, in order to conserve its angular momentum. The induction of the swirl velocity on the injected jet destructs one of the two parts of the kidney vortex which entrains fluid from the cross flow to the jet promoting the mixing between the two fluids, while the trace of a swirled jet remains closer to the wall downstream of the injection hole. Finally, the use of contra rotating jet or fan configurations reduces the wall shear stress in a very great extent, leading to better thermal protection of turbine blades, as well as cancels out the yaw torques of each fan separately, resulting in better flight control of typical lift surface.

Commentary by Dr. Valentin Fuster
2010;():843-852. doi:10.1115/GT2010-23389.

Helicopter mission performance analysis has always been an important topic for the helicopter industry. This topic is now raising even more interest as aspects related to emissions and noise gain more importance for environmental and social impact assessments. The present work illustrates the initial steps of a methodology developed in order to acquire the optimal trajectory of any specified helicopter under specific operational or environmental constraints. For this purpose, it is essential to develop an integrated tool capable of determining the resources required (e.g. fuel burnt) for a given helicopter trajectory, as well as assessing its environmental impact. This simulation framework tool is the result of a collaborative effort between Cranfield University (UK), National Aerospace Laboratory NLR (NL) and LMS International (BE). In order to simulate the characteristics of a specific trajectory, as well as to evaluate the emissions that are produced during the helicopter’s operation within the trajectory, three computational models developed at Cranfield University have been integrated into the simulation tool. These models consist of a helicopter performance model, an engine performance model and an emission indices prediction model. The models have been arranged in order to communicate linearly with each other. The linking has been performed with the deployment of the OPTIMUS process and simulation integration framework developed by LMS International. The optimization processes carried out for the purpose of this work have been based on OPTIMUS’ built-in optimizing algorithms. A comparative evaluation between the optimized and an arbitrarily defined baseline trajectory’s results has been waged for the purpose of quantifying the operational profit (in terms of fuel required) gained by the helicopter’s operation within the path of an optimized trajectory for a given constraint. The application of the aforementioned methodology to a case study for the purpose of assessing the environmental impact of a helicopter mission, as well as the associated required operational resources is performed and presented.

Topics: Simulation
Commentary by Dr. Valentin Fuster
2010;():853-865. doi:10.1115/GT2010-23393.

A combined cycle gas turbine generating power and hydrogen is proposed and evaluated. The cycle embodies chemical looping combustion (CLC) and uses a Na based oxygen carrier. In operation, a stoichiometric excess of liquid Na is injected directly into the combustion chamber of a gas turbine cycle, where it is burnt in compressed O2 produced in an external air separation unit (ASU). The resulting combustion chamber exit stream consists of hot Na vapour, and this is expanded in a turbine. Liquid Na2 O oxide is also generated in the combustion process, but this can be separated, readily, from the Na vapour and collects in a pool at the bottom of the reactor. To regenerate liquid Na from Na2 O, and hence complete the chemical loop, a reduction reactor (the reducer) is fed with three streams: the hot Na2 O from the oxidiser; the Na vapour (plus some entrained wetness) exiting a Na-turbine; and a stream of solid fuel, which is assumed to be pure carbon for simplicity. The sensible heat content of the liquid Na2 O and latent and sensible heat of the Na vapour provide the heat necessary to drive the endothermic reduction reaction and ensure the reducer is externally adiabatic. The exit gas from the reducer consists of almost pure CO which can be used to generate by-product H2 using the water-gas shift reaction. A mass and energy balance of the system is conducted assuming reactions reach equilibrium. The analysis allows for losses associated with turbomachinery; heat exchangers are assumed to operate with a finite approach temperature; however, pressure losses in equipment and pipework are assumed negligible — a reasonable assumption for this type of analysis that will still yield meaningful data. The analysis confirms that the combustion chamber exit temperature is limited by both first and second law considerations to a value suitable for a practical gas turbine. The analysis also shows that the overall efficiency of the cycle, under optimum conditions and taking into account the work necessary to drive the ASU, can exceed 75%.

Commentary by Dr. Valentin Fuster
2010;():867-875. doi:10.1115/GT2010-23420.

Most state-of-the-art natural gas fired combined cycle (NGCC) plants are triple-pressure reheat cycles with efficiencies close to 60 percent. However, with carbon capture and storage, the efficiency will be penalized by almost 10 percent units. To limit the energy consumption for a carbon capture NGCC plant, exhaust gas recirculation (EGR) is necessary. Utilizing EGR increases the CO2 content in the gas turbine exhaust while it reduces the flue gas flow to be treated in the capture plant. Nevertheless, due to EGR, the gas turbine will experience a different media with different properties compared to the design case. This study looks into how the turbo machinery reacts to EGR. The work also discusses the potential of further improvements by utilizing pressurized water rather than extraction steam as the heat source for the CO2 stripper. The results show that the required low-pressure level should be elevated to a point close to the intermediate-pressure to achieve optimum efficiency; hence one pressure level can be omitted. The main tool used for this study is an in-house off-design model based on fully dimensionless groups programmed in the commercially-available heat and mass balance program IPSEpro. The model is based on a GE 109FB machine with a triple-pressure reheat steam cycle.

Commentary by Dr. Valentin Fuster
2010;():877-885. doi:10.1115/GT2010-23428.

After a shaft failure the compression system of a gas turbine is likely to surge due to the heavy vibrations induced on the engine after the breakage. Unlike at any other conditions of operation, compressor surge during a shaft over-speed event is regarded as desirable as it limits the air flow across the engine and hence the power available to accelerate the free turbine. It is for this reason that the proper prediction of the engine performance during a shaft over-speed event claims for an accurate modelling of the compressor operation at reverse flow conditions. The present study investigates the ability of the existent two dimensional algorithms to simulate the compressor performance in backflow conditions. Results for a three stage axial compressor at reverse flow were produced and compared against stage by stage experimental data published by Gamache. The research shows that due to the strong radial fluxes present over the blades, two dimensional approaches are inadequate to provide satisfactory results. Three dimensional effects and inaccuracies are accounted for by the introduction of a correction parameter that is a measure of the pressure loss across the blades. Such parameter is tailored for rotors and stators and enables the satisfactory agreement between calculations and experiments in a stage by stage basis. The paper concludes with the comparison of the numerical results with the experimental data supplied by Day on a four stage axial compressor.

Commentary by Dr. Valentin Fuster
2010;():887-897. doi:10.1115/GT2010-23492.

Over the past few years, an intensive effort has been put forth to reduce gas turbine engine generated pollutants, as well as fuel consumption. The current research team understanding the motives behind this effort, suggests an alternative method of wet compression that of using fuel as a cooling medium. Fundamentally, the method of wet compression with fuel injection is based on the same principles of wet compression incorporating water injection. However, there are some considerable differences between the two approaches. A thorough comparison has been carried out revealing each method’s advantages and disadvantages. Following the initial comparison of the two methods, the study goes a step further by investigating the applicability of wet compression incorporating fuel. The investigation has taken into account the characteristics of the axial flow compressor where a typical aviation fuel was injected. However, in order to acquire all the necessary information before putting method’s applicability into context, the differences between dry compression and wet compression with fuel injection were examined. In this new approach, the compressor is the engine component where the fuel is injected first, thus a preliminary design study was carried out along an axial compressor’s mean radius line. Finally the computation has been carried out for both dry and wet compression techniques. Compressor’s specifications were similar to J85’s compressor whereas fuel’s specifications were based on JP-8’s properties. Compressor’s geometry and design point performance, were computed using a mean line analysis domestic code. A brief analysis of the code will be given, including both the initial version that was used for the dry compression calculations, as well as the modified one that was used for the wet compression calculations. After that, the presentation of the results follows. Finally, the paper will be concluded with a discussion of the findings and wet compression’s with fuel injection perspectives.

Commentary by Dr. Valentin Fuster
2010;():899-908. doi:10.1115/GT2010-23562.

Sub-idle is a very challenging operating region, as the performance of a gas turbine engine changes significantly compared to design conditions. In addition, the regulations for new and existing engines are becoming stricter and the prediction of engine relight capability is essential. In order to predict the performance of an engine, detailed component maps are required. The data obtained from rig tests is insufficient at low speeds, creating the need for generation of maps within the sub-idle regime. The first step towards this direction is the use of an extrapolation process. This is a purely mathematical process and the results are not usually of sufficient accuracy. In addition, this method does not provide any insight on the physical phenomena governing the operation of the compressor at low speeds. The accuracy of the resulting compressor map can be increased with a better low speed region definition; this can be achieved via the thorough study of a locked rotor compressor, enabling the derivation of the zero rotational speed line and allowing an interpolation process for the generation of the low speed part of the characteristic. In this work an enhanced sub-idle compressor map generation technique is proposed. The suggested methodology enables the generation of characteristics at far off-design conditions with enhanced physical background. Alternative parameters for map representation are also introduced. Provided that the all the blade rows of the compressor are of known geometry, a numerical analysis is used for the calculation of the characteristic of the half stage and a stage stacking method is employed to create the entire compressor characteristic. This way, the sub-idle region of the map can be calculated through interpolation, which provides a more accurate and predictive technique. The application to compressor maps showed that the methodology proposed is robust and capable to enhance any performance simulation tool used for the prediction of transient altitude relight or groundstarting manoeuvres.

Topics: Compressors
Commentary by Dr. Valentin Fuster
2010;():909-920. doi:10.1115/GT2010-23621.

Reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, as well as the reduction of engine nacelle drag and weight. Conventional turbofan designs however that reduce CO2 emissions — such as increased OPR designs — can increase the production of NOx emissions. In the present work, funded by the European Framework 6 collaborative project NEWAC, an aero engine multidisciplinary design tool, TERA2020, has been utilised to study the potential benefits from introducing heat-exchanged cores in future turbofan engine designs. The tool comprises of various modules covering a wide range of disciplines: engine performance, engine aerodynamic and mechanical design, aircraft design and performance, emissions prediction and environmental impact, engine and airframe noise, as well as production, maintenance and direct operating costs. Fundamental performance differences between heat-exchanged cores and a conventional core are discussed and quantified. Cycle limitations imposed by mechanical considerations, operational limitations and emissions legislation are also discussed. The research work presented in this paper concludes with a full assessment at aircraft system level that reveals the significant potential performance benefits for the inter-cooled and intercooled recuperated cycles. An intercooled core can be designed for a significantly higher OPR and with reduced cooling air requirements, providing a higher thermal efficiency than could otherwise be practically achieved with a conventional core. Variable geometry can be implemented to optimise the use of the intercooler for a given flight mission. An intercooled recuperated core can provide high thermal efficiency at low OPR values and also benefit significantly from the introduction of a variable geometry low pressure turbine. The necessity of introducing novel lean-burn combustion technology, to reduce NOx emissions, at cruise as well as for the landing and take-off cycle, is demonstrated for both heat-exchanged cores and conventional designs. Significant benefits in terms of NOx reduction are predicted from the introduction of a variable geometry low pressure turbine in an intercooled core with lean-burn combustion technology.

Commentary by Dr. Valentin Fuster
2010;():921-931. doi:10.1115/GT2010-23685.

Solar thermal power plants have been constructed over the past two decades to reduce harmful emissions and provide a long-term solution for oil independent electricity generation. Of the solar power plant solutions, Rankine cycle based machines have most widespread uses. This study focuses on the modeling of a solar retrofit to a typical combined cycle power plant. The goal is to operate the plant 17 hours per day, making use of thermal storage capability so that the plant may operate even during a portion of the night time. The plant will be located in Orlando, Florida to take advantage of the abundance of sun in that geographic location. On the cycle side, the amount of solar collectors, the working fluid, and the turbine are considered. The thermal storage system, on the other hand, must be designed based upon a balance between cost and storage density. A decision will be made from existing sensible heat solid storage materials. The storage material evens out the energy supplied to the turbine working fluid between the peak solar radiation of the day time and the absence of solar radiation at night. This plant can be implemented in two ways: as a completely newly constructed power plant or as an addition to a HRSG (Heat Recovery Steam Generation) configuration, which can be retrofitted to an existing combined cycle power plant to increase its overall efficiency. In this study, the addition of a solar air collection system with a storage unit to a HRSG combined cycle power plant is proposed. The HRSG will be designed using a series of energy balances for each component. This proposed plant will then be compared with a similar solar plant to examine its feasibility in terms of land area. The storage unit devised comprises 1377 m3 and stores approximately 3900 GJ of thermal energy, which equates to 8 hours of run time when solar radiation is not available. The benefit of this addition to the plant is that the storage reduces the gas turbine run time necessary to provide hot gas to the HRSG. The total cost of the storage medium is approximately $8 million.

Commentary by Dr. Valentin Fuster
2010;():933-943. doi:10.1115/GT2010-23729.

The Power, Water Extraction, and Refrigeration (PoWER) engine has been investigated for several years as a distributed energy system, among other applications, for civilian or military use. Previous literature describing its modeling and experimental demonstration have indicated several benefits, especially when the underlying semi-closed cycle gas turbine is combined with a vapor absorption refrigeration system, the PoWER system described herein. The benefits include increased efficiency, high part-power efficiency, small lapse rate, compactness, less emission, air, and exhaust flows (which decrease filtration and duct size) and condensation of fresh water. The present paper describes the preliminary design and modeling of a modified version of this system as applied to distributed energy, especially useful in regions which are prone to major grid interruptions due to hurricanes, under - capacity, or terrorism. In such cases, the distributed energy system should support most or all services within an isolated service island, including ice production, so that the influence of the power outage is limited in scope. This paper describes the rather straightforward system modifications necessary for ice production. The primary focus of the paper is the use of this ice-making capacity to achieve significant load-leveling during the summer utility peak, hence reducing the electrical capacity requirements for the grid as well as load-leveling strategies.

Commentary by Dr. Valentin Fuster
2010;():945-952. doi:10.1115/GT2010-23791.

This paper describes technological of a fuel processor for hydrogen production able to convert 10 cubic meters of methane per hour. This device has been developed to feed hydrogen CHP suitable for the most common residential applications. The measured conversion efficiencies are extremely high: after the steam reformer the results are 76%H2; 18%CO2; 0,5%CH4; 5%CO; but the carbon monoxide is totally reduced throughout the water gas shift and the partial oxidation which contemporarily increase the hydrogen to over 77%. According to these results, this fuel processor is one of the first middle sized reformer to achieve, at comparable costs per cubic meter, conversion performance that were normally obtained only by industrial reforming plants.

Commentary by Dr. Valentin Fuster
2010;():953-963. doi:10.1115/GT2010-23793.

Injection of water droplets into industrial gas turbines in order to boost power output is now common practice. The intention is usually to saturate and cool the intake air, especially in hot and dry climates, but in many cases droplets carry over into the compressor and continue to evaporate. Evaporation within the compressor itself (often referred to as “overspray”) is also central to several advanced wet cycles, including the Moist Air Turbine (MAT) and the so-called TOPHAT cycle. The resulting wet compression process affords a number of thermodynamic advantages, such as reduced compression work, and increased mass flow rate and specific heat capacity of the turbine flow. Against these benefits, many of the compressor stages will operate at significantly off-design flow angles, thereby compromising aerodynamic performance. The current paper describes wet compression calculations including velocity slip and many of the associated phenomena (e.g., blade deposition and film evaporation). The calculations also allow for a poly-dispersion of droplet sizes and droplet temperature relaxation effects (i.e., the full droplet energy equation is solved rather than assuming that droplets adopt the wet-bulb temperature). The latter is important for sprays produced by “flashing” since the resulting droplets are initially much hotter than the surrounding gas. The method has been applied to a “generic” twelve stage compressor to ascertain to the impact slip effects have on the wet compression process.

Topics: Compression
Commentary by Dr. Valentin Fuster

Marine

2010;():965-973. doi:10.1115/GT2010-22122.

The LHD 8 amphibious assault ship utilizes a hybrid propulsion plant, where the ship has the capability to be propelled by electric propulsion motors or gas turbine engines all of which is controlled and monitored by a state-of-the-art Machinery Control System (MCS). Unlike the previous ships of the class which were steam powered, the hybrid drive is designed to allow economical low speed fuel efficiency on electric motors as well as a traditional gas turbine power plant for all other mission areas. This will yield significant fuel savings over the life of the ship. The integrated machinery control system is likewise expected to reduce life cycle costs through reduced manning. After a successful series of sea trials, the LHD 8, Makin Island was delivered to the US Navy on April 2009 and departed the builders’ yard in July 2009 for a transit around the tip of South America to her homeport of San Diego, CA. The paper discusses the results of Builders and Acceptance Trials as well as the in-service experience of the ship on her maiden voyage. Examples are given of predicted vs. expected fuel consumption rates, design issues encountered and corrective measures taken as well as feedback from operators on the overall machinery plant design the MCS and its ease of operation. Included in the paper are ship drawings, photos and diagrams.

Topics: Design , Navy
Commentary by Dr. Valentin Fuster
2010;():975-984. doi:10.1115/GT2010-22217.

Energy conservation measures currently employed by U.S. Navy surface combatants require labor-intensive, time-consuming data entry from which fuel curves are generated to drive each ship’s propulsion plant machinery alignment. From these rudimentary curves optimal transit speeds, configurations, and refueling requirements are determined for specific operational demands and mission profiles. This paper describes an automated process for optimizing shipboard fuel consumption rates by integrating advanced diagnostic and maintenance optimization techniques with the onboard data information system. The automated energy conservation decision support system described herein addresses fossil fuel propulsion (gas turbines, steam turbines, and diesel engines), power generation and auxiliary systems. The software tool consists of diagnostic, fuel management, and maintenance modules. The diagnostic module tracks and trends the health state of components that use fuel (and their supporting systems) to provide real-time information on the impact of their current condition on fuel consumption. The fuel management module automates data collection and the generation of fuel curves through open-systems architecture communication with ICAS. It also enables planning by recommending an optimal machinery configuration to minimize fuel consumption based on either speed or time to destination constraints. Additionally, a fuel management module provides real-time information on fuel consumption and optimizes the load of each component based on its health condition, operating requirements and the number and condition of similar components. Finally, overall decision support comes from the maintenance management module that tracks the maintenance actions being performed on fuel consuming systems and recommends future maintenance to be performed (from a fuel conservation standpoint) based on current health information.

Commentary by Dr. Valentin Fuster
2010;():985-992. doi:10.1115/GT2010-22305.

The LHD 8 amphibious assault ship utilizes a hybrid propulsion plant, where the ship has the capability to be propelled by electric propulsion motors or gas turbine engines, all of which is controlled and monitored by a state-of-the-art Machinery Control System (MCS). Unlike the previous ships of the class which were steam powered, the hybrid drive is designed to allow economical low speed fuel efficiency on electric motors as well as a traditional gas turbine power plant for all other mission areas. This is expected to yield significant fuel savings over the life of the ship. The integrated machinery control system is likewise expected to reduce life cycle costs through reduced manning. The build specification for this ship class required that all MCS signals including the gas turbine alarms and shutdown functions be fully tested prior to initial light-off. Many of these functions are not activated, and therefore cannot be tested, until the Electronic Control Unit (ECU) senses that the gas turbine is running. Historically, previous ship classes used a manually-operated set of potentiometers to provide signals to a gas turbine ECU to simulate external inputs to allow testing of shutdown and alarm functions. For this newest class of engine however, the ECU is significantly more complex and requires the ECU to successfully progress through the start sequence, including sensed variables changing at expected rates, in order to activate the alarm and shutdown logic. In order to test this functionality, an engine simulator, physically interfaced to the ECU aboard the ship, was necessary. No system of this type is available or had ever been developed. Neither the engine or ECU manufacturer had a device for this purpose. The paper will discuss the development and implementation of a gas turbine simulator that incorporates an engine mathematical model fully compatible with the ECU controller, simulation hardware capable of supporting real-time system performance, signal conditioning necessary to provide/accept raw signals to/from the ECU, as well as a host laptop with software necessary to control simulator/stimulator and perform test functions. The paper will discuss the system requirements development, component selection, software and hardware development, and system integration and testing. Also discussed will be the results of bench testing as well as the final shipboard test results. Examples in the form of diagrams, photos, charts and schematics will be used. The paper will conclude with a discussion of the benefits of a dynamic gas turbine simulator and potential future applications.

Topics: Propulsion , Turbines , Ships
Commentary by Dr. Valentin Fuster
2010;():993-1012. doi:10.1115/GT2010-22472.

Earlier steam plant design requirements for the US Navy steam turbines were focused on reliability and maintainability. Simplicity of design implied easy operation, maintenance and service. Efficiency was not a top priority. Now, in an atmosphere of operating budget cuts and skyrocketing fuel costs along with environmental responsibilities, efficiency improvements are expected, and in some cases demanded on main propulsion units. Additional load due to modern electronic combat systems places extra demand on SSTG sets. Modernization with improved efficiency, reliability and maintainability, while retaining design simplicity is the optimal solution. Meanwhile during the last 50 years, the turbomachinery industry has developed numerous innovative improvements through extensive R&D efforts, advanced computerized simulation of aerodynamics and flow field analysis along with finite element modeling, new manufacturing methods and improved metallurgy and surface treatments. These advances allow efficiency improvements without adding complexity to the design. Modern airfoil design, the optimized transition from partial-arc to full-arc steam admission, tangential leaning vanes, advanced seal designs, streamlined steam path configuration and improved moisture removal are major areas worthy of consideration. Mechanical reliability can be improved with Taumel (orbital) peened tenons for blade packets or integral shrouds which give a 360 degree connection to all of the blades in a row. Electron beam welded diaphragms with EDM cut horizontal joints help to minimize thermal distortions and flow irregularities, particularly at the split lines. Improved welding procedures for casing, diaphragm and rotor repairs can result in shorter repair cycles and lower costs to further promote extension of the turbine’s life cycle. Maintainability can be improved with advanced materials that no longer require regular service, such as anti-lube (greaseless) bushings and replaceable components that don’t require in place machining. Combinations of the above improvements have been used successfully within the industry in upgrading hundreds of turbines, compressors and pumps in various applications including power generation, petrochemical, oil and gas, commercial marine, and other fields. Typical examples of efficiency improvement are 8%–14% over current operating parameters. [1, 2, 3, 4, 5] This paper presents various proven advanced turbine components used to upgrade existing steam turbines, which can be successfully used in US Navy applications as well.

Commentary by Dr. Valentin Fuster
2010;():1013-1019. doi:10.1115/GT2010-22767.

Currently, the U.S. Navy DDG-51 class ships employ a system of piping, tanks, and nozzles for washing the four Gas Turbine Main (GTM) engines and three Ship Service Gas Turbine Generator (SSGTG) engines. The wash system employed, referred to as the crankwash system, allows the user to wash the compressor section of a gas turbine only when the turbine in question is not operating. On a DDG-51 class ship, it is possible to utilize the existing crankwash piping, tank, and overall architecture to supply water to an online water wash system. An online water wash system allows the compressor section to be cleaned while the gas turbine is in operation. This is intended to reduce the periodicity of crankwashing and associated starter cycling costs. Online water wash is also intended to maintain compressor cleanliness in the interval between crankwashes. NAVSEA Philadelphia researched appropriate online water wash system designs, methods for collecting data to address fuel savings and engine performance issues, and installation methods. GTM and SSGTG Online Water Wash Systems were then installed on USS PREBLE (DDG-88) in late 2008. USS PREBLE subsequently deployed for a period of six months beginning January 2009. During the deployment, data was collected as the systems were operated. This paper will discuss the system design, provide data analysis results, and discuss lessons learned.

Topics: Gas turbines , Navy , Ships
Commentary by Dr. Valentin Fuster
2010;():1021-1028. doi:10.1115/GT2010-22804.

For the past 40 years, the United States Navy has utilized a standardized machinery configuration on its surface combatant cruisers and destroyers. Large gas turbines (18.5 MW) directly coupled to a twin screw drive train and smaller gas turbine engines (2.5–3.0 MW) feeding a common electrical bus provided ships propulsion and power requirements. This consistent design approach afforded an opportunity for the Navy to hone its operational and maintenance strategies with a focus on enhancing reliability. DDG 1000 provides a unique machinery arrangement with which the Unites States Navy has minimal operational experience, with small and large Gas Turbine prime movers all producing power to an integrated power distribution network servicing both propulsion and ships service power requirements. This new all electric platform design produces some unique challenges for both the prime movers and electrical distribution. This paper explores gas turbine operating profile, reliability centered maintenance, transient engine response, power quality requirements and power distribution architecture as they apply to this new surface combatant. Comparisons will be drawn between the Navy’s legacy system applications with an emphasis on how the new ship design requires innovative support approaches. Additionally, contrasts are articulated between defined military specifications and testing requirements for legacy applications and the amorphous standards for dual spool applications.

Commentary by Dr. Valentin Fuster
2010;():1029-1035. doi:10.1115/GT2010-22811.

In 1999, the United States Navy implemented an LM2500 High Pressure Turbine Blade Refurbishment Program. Traditionally, the US Navy had replaced high pressure turbine components each time an engine was removed from a ship during its depot overhaul visit. Following successful testing of several Rainbow rotors built up with refurbished LM2500 blades, as well as experience gained by the Royal Australian Navy, refurbishment of stage 1 and 2 high pressure turbine blades was adopted vice the replace with new part strategy previously utilized. This paper takes a fresh look at the blade refurbishment effort from two perspectives, first, an updated technical assessment is made of Rainbow rotor components as well as parts which were implemented as part of the refurbishment program to evaluate their current (2009) condition and define service life expectations. Secondly, a financial assessment is made of the program itself, defining the cost avoidance of refurbishing customer owned blades versus the cost to procure new components. The financial analysis will also include commentary on risk mitigation based upon the hundreds of thousands of operating hours on these components have acquired while deployed at sea.

Commentary by Dr. Valentin Fuster
2010;():1037-1046. doi:10.1115/GT2010-23155.

The gas turbine engine first went to sea in 1953 when the British Shipbuilding Company VOSPERS was selected to experiment with the gas turbine as a form of marine propulsion. The former Steam Gun Boat (SGB) HMS Grey Goose was rebuilt by the shipyard with the surprisingly sophisticated Rolls-Royce RM60 engine. Today, for any vessel project whose design function makes its speed or volume critical, the gas turbine has become a strong candidate for selection as a prime mover, due to its inherent power density and low weight. For marine use, the gas turbine is equipped with a power turbine in order to convert the energy in the exhaust gases into rotational energy. This energy is applied, via a shaft line, to a suitable propulsion system either by a direct mechanical drive system or by the intermediary of an electrical system: this is the case of yachts and mega yachts characterized by high speed performances. The case study concerns the motor yacht “OCI CIORNIE”, built by the shipyard PALMER JOHNSON in 1999 and powered with a CODAG (Combined Diesel and Gas) type propulsion plant made up of two diesel engines coupled to waterjets, via a reduction gear and by a gas turbine TF40, driving a surface piercing propeller (SPP) with Arneson transmission, via a reduction gearbox. According to expectations of the designer the top speed with the CODAG configuration was to be more than 55 knots while the speed with the only diesel engines running would be around 25 knots, but enough to reach the take off speed anyway. Instead, because of weight increase during the construction, the current maximum speed with the diesel propulsion is only 14÷16 knots, depending of the displacement and the sea condition, while the CODAG propulsion top speed is around 50÷52 knots. The paper will analyze the main steps of the development of the OCI CIORNIE project and will compare the performances of the planning stage with the final operating conditions of the yacht. Besides, the paper will consider, for the current displacement reached, the optimum distribution between the power of the diesel engines and the power of the gas turbine in order to obtain, for different speeds, the maximum range, the minimum wear and tear of the machines and, as a consequence, the minimum operating expenses, respecting the restrictions of the maximum torque on the gas turbine and on the diesel engines.

Topics: Power stations , Boats
Commentary by Dr. Valentin Fuster
2010;():1047-1054. doi:10.1115/GT2010-23459.

This paper discusses the evolution of marine gas turbine (MGT) maintenance practices on the US Navy landing craft, air cushion (LCAC). This includes the progression from the philosophy of remove, replace and depot repair of engine modules, to a more condition based maintenance (CBM) practice. Included is the original concept of reusing all common TF40B parts, allowing the ETF40B to be created from a kit. The TF40B engine is being retired while the LCAC Service Life Extension Program (SLEP) is implemented. The propulsion part of the SLEP includes an ETF40B engine. Historically, the TF40B engine would be returned to a depot for repair. Supporting this in the past has relied on a costly and time consuming depot repair methodology. This paper will explore repair and overhaul approaches associated with the evolution of the US Navy’s philosophy. It will show the benefits of applying more on-condition type repairs, which will lead into a conditioned based overhaul (CBO) concept. There are discussions of the CBM concept that supports the current fleet. It delivers a large reduction in support costs and time consumption at a time of budget cuts and increased repair turn-around times from industry reductions in available parts and labor.

Topics: Maintenance , Engines , Navy
Commentary by Dr. Valentin Fuster
2010;():1055-1060. doi:10.1115/GT2010-23462.

There are various methods used to start marine gas turbine engines on large naval surface combatants. Methods include pneumatic, mechanical, hydraulic, and electric starting systems. This paper gives an overview of basic starting requirements, describes each method used on large surface combatants, and identifies which systems are used on many of the U.S. Navy surface combatants.

Topics: Gas turbines , Navy
Commentary by Dr. Valentin Fuster
2010;():1061-1068. doi:10.1115/GT2010-23488.

This paper examines the utilization of Landing Craft, Air Cushion (LCAC) historical operational data, empirical knowledge and emergent lifecycle topics to refine the operational profile of LCAC and other air cushion vehicles. Since 1986, the United States Navy’s (USN) LCAC vehicle has accumulated sizeable operational hours in a unique and rigorous environment. Such a distinctive operating environment prohibits singular application of a surface ship or aircraft operational profile. Addressing emergent lifecycle issues, such as fleet wide main engine 4th nozzle failures, the need for a refined operating profile has been identified. Presently, all component life limit forecasting and inspection criterion are dictated by an antiquated notional operating profile, which utilize inadequate cycling assumptions. Furthermore, existing practice records total operational hours and main engine start data. Neither variable correspond to cyclic data. Improved accuracy of the mission profile will assist in drive-train component life limit assessment and critical inspection criteria. This paper will expand upon generation of a refined operation profile tailored to air cushion vehicle operation based upon service history, mission requirements and testing.

Topics: Vehicles
Commentary by Dr. Valentin Fuster
2010;():1069-1078. doi:10.1115/GT2010-23596.

In the 1950’s and 1960’s, the United States Navy (USN) embarked on an ambitious program to convert surface combatants from steam to gas turbine power. Navy unique engines were developed and commercial industrial engines were modified to meet the strenuous environments encountered by surface Navy ships. Ultimately, the best engines were found to be those developed from the aero-industry. However, those aero-derivative engines lacked shock hardness, vibration treatment and most importantly, they lacked the ability to survive long hours of operation in a heavy salt environment burning diesel and other poorer fuels. Those poorer fuels contained higher levels of sulfur and other chemical compounds that created a challenging environment for the aircraft engines. The aircraft engines were designed to burn much cleaner fuel with virtually no sea salt. As a result, early applications of those engines to Navy ships were disappointing. However, through aggressive materials development programs and extended endurance tests in a marine-like environment, engines including the Pratt and Whitney FT-4A and the General Electric LM2500 demonstrated themselves to be superior replacements for traditional Navy steam propulsion plants. The LM2500 eventually became the workhorse of the USN surface fleet and has proven to be an excellent engine. Nevertheless, as fuels become more costly and quality sometimes questionable, the Navy is interested in another leap forward. This leap is anticipated to again be based on aero-derivative engines, but will be focused on smaller, lighter, and more fuel efficient engines that will have the capability of burning the alternative fuels of the future. The Office of Naval Research (ONR) is contemplating a comprehensive program of materials developments, Phase I, which will facilitate the marinization of the highly efficient gas turbine engines being developed in various Air Force and commercial engine development programs. Marinization issues could include improving the performance of ceramic matrix composites in a marine environment and minimizing the affects of higher temperatures on disc corrosion in the final stages of the compressor and in the hot-section. A Phase II program is also contemplated that will then develop a series of engines for various future USN applications based on the results of the Phase I Program. This paper will describe the programs that are being contemplated.

Commentary by Dr. Valentin Fuster
2010;():1079-1087. doi:10.1115/GT2010-23659.

This paper will trace the history and development of the TF series marine gas turbines over the last 40 years leading up to today’s candidate for the US Navy Ship-to-Shore Connector (SSC) program, the model TF60B, and its planned successor the TF70. The TF60B engine traces its ancestry to helicopter engines designed by Avco-Lycoming in the early 1960s. This paper will review the extensive experience-based development of the original T55-L-5 into the first of the marine engines (the TF20) and then through the TF25, TF35, TF40, to today’s ETF40B, TF50A and TF60B. Specific improvements and power increases will be described with each significant model revision along with the unique requirements of the air cushion vehicle and similar platforms that were powered by these engines. The specific characteristics that define the TF series engine as proven marine propulsion units will be discussed in each of the subsequent engine models. The paper will show the steady progression of advancement in aerodynamics, materials, temperatures, controls and structures leading to today’s next generation engine, the TF60B, with the path to yet higher levels of power for the future. The current evolutionary TF60B engine will be described in terms of architecture and development philosophy highlighting the foresight of the original design to accommodate the increments of growth without significantly increasing the frame size of the gas turbine.

Commentary by Dr. Valentin Fuster
2010;():1089-1098. doi:10.1115/GT2010-23795.

The development of the Littoral Combat Ship (LCS) and its life cycle support design objectives were driven by three key objectives: 1) High level of ship mission availability while performing any one of the three mission capabilities; 2) Minimal Total Ownership Cost (TOC); 3) Manning compliment lower than the similar predecessor class of ships. To achieve these concurrent goals, the ship design provides functionality including advanced automation for machinery control, as well as mission function reconfiguration and execution. Unfortunately, information-based automated machinery reliability management decision support was not part of the ship design. This type of decision support is vital in enabling a significantly reduced crew and the advance planning required for executing the scheduled short maintenance availabilities. Leveraging existing equipment monitoring technologies deployed throughout the legacy fleet with the reliability engineering approach on LCS will improve the operational availability of gas turbine propulsion systems and allow executing the ship’s Concept of Operations (CONOPS). To address the reliability and TOC risks with the initially defined sustainment approach, a Reliability Engineering derived Condition Based Maintenance (CBM) strategy was developed, such that it could be implemented using a proven remote monitoring infrastructure. This paper will describe the Reliability Engineering based CBM approach and how it will be implemented on the LCS-1 and LCS-2 propulsion gas turbine engines and other critical systems to achieve system level operational reliability, the LCS life cycle support design objectives, and defined sustainment strategies.

Commentary by Dr. Valentin Fuster
2010;():1099-1104. doi:10.1115/GT2010-23796.

Three-shaft gas turbine was applied to marine electric propulsion system. The dynamic performance and control strategy of the three-shaft marine electric propulsion gas turbine arrested investigator’s attention, because they are very different from that of single-shaft gas turbine due to the complicated rotor structure. In this study, a model of nonlinear differential equation set is built to calculate the dynamic performance of three-shaft gas turbine and a simulation model of three-shaft marine electric propulsion gas turbine is constructed using the platform of MATLAB/SIMULINK. An adaptive software is developed for three-shaft gas turbine simulation. The new matching problems and changing rules among parameters are investigated in the case of load rejection of marine electric propulsion system. Multi-closed loop control system, instead of traditional control system, is introduced in order to improve the system quality and safety.

Commentary by Dr. Valentin Fuster

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