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ASME Conference Presenter Attendance Policy and Archival Proceedings

2013;():V004T00A001. doi:10.1115/GT2013-NS4.
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This online compilation of papers from the ASME Turbo Expo 2013: Turbine Technical Conference and Exposition (GT2013) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Ceramics

2013;():V004T02A001. doi:10.1115/GT2013-94061.

Lower thermal conductivity and high temperature stability are the two properties which are highly desired from ceramic top coat materials in TBC systems. Gadolinium Zirconate, Gd2Zr2O7, (GdZ) and Dyprosia Stabilized Zirconia (DySZ) are two of the candidate materials with such properties and consequently the TBC system would be able to work at higher turbine inlet temperature (TIT) or the lifetime can be increased. In the present study, life time measurements are done for single and double layered Electron Beam Physical Vapor Deposition (EB-PVD) GdZ and DySZ samples by thermal-cycling tests. The double layered TBCs consisted of a thin 7YSZ layer and, on top, the new candidate material. Both single and double layered samples of GdZ and DySZ have shown similar or better lifetimes than the standard 7YSZ samples. However, single layered TBCs showed better lifetime results than the respective double layers. In this study, changes in the microstructure, diffusion of elements and sintering of the TBC materials with aging are observed.

Commentary by Dr. Valentin Fuster
2013;():V004T02A002. doi:10.1115/GT2013-94095.

Ceramic Matrix Composite (CMC) materials are an attractive design option for various high-temperature structural applications. In particular, the use of CMC materials as a replacement for state-of-the-art nickel-based superalloys in hot gas path turbomachinery components offers the potential for significant increases in turbine system efficiencies, due largely to reductions in cooling requirements afforded by the increased temperature capabilities inherent to the ceramic material. However, two-dimensional fabric-laminated CMCs typically exhibit low tensile strengths in the thru-thickness (interlaminar) direction, and interply delamination is a concern for some targeted applications. Currently, standardized test methods only address the characterization of interlaminar tensile strengths at ambient temperatures; this is problematic given that nearly all CMCs are slated for service in high-temperature operating environments. This work addresses the development of a new test technique for the high-temperature measurement of interlaminar tensile properties in CMCs, allowing for the characterization of material properties under conditions more analogous to anticipated service environments in order to yield more robust component designs.

Commentary by Dr. Valentin Fuster
2013;():V004T02A003. doi:10.1115/GT2013-94679.

In the framework of the High Performance Oxide Ceramics program (HiPOC), three different oxide/oxide ceramic matrix composite (CMC) materials are studied for a combustion chamber application in continuation of the work reported in Gerendas et al. [1]. A variation in the micro-structural design of the three CMC materials in terms of different fiber architecture and matrix processing are considered in a first work stream. By modification of the matrix and the fiber-matrix interface as well as the application of an environmental barrier coating (EBC), the high temperature stability is enhanced. Furthermore, design concepts for the attachment of the CMC component to the metal structure of the engine are finalized in a second work stream. Issues like sealing of cooling leakage paths, allowance for the different thermal expansion and the mechanical fixation are addressed. An interim standard of the mechanical attachment scheme is studied on a shaker table. Also the friction coefficient between the metallic and ceramic components is analyzed in order to set the proper tightening torque. The manufacturing of the CMC combustor is improved in several iterations in order to achieve a high quality material with optimized fiber architecture. Afterwards, two CMC materials are selected for the combustion testing and the finalized design of the metallic and CMC components is manufactured. A fit check is performed prior to EBC application and laser drilling of the effusion holes in order to evaluate the impact of the manufacturing tolerances on the function of the sealing and attachment scheme and to correct small issues at this stage. First results from the validation testing in a high-pressure tubular combustion rig up to a Technology Readiness Level 4 (TRL4) are reported.

Commentary by Dr. Valentin Fuster
2013;():V004T02A004. doi:10.1115/GT2013-94728.

Ceramic matrix composite (CMC) materials technology is of fundamental importance to gas turbine engine application. FOD (foreign Object Damage) in CMC components can result in component localized damage and a loss of post-impact performance. CMC impact generates a varying degree of damage from localized surface damage to complete penetration depending on the severity of impact events. Ceramic Composite equivalent electrical properties are computed based on simplified Multi-scale micromechanics equations. Electrical resistance and/or conductivity are computed utilizing the constituent material properties, effective medium, and percolation theories. Ceramic composite electrical properties simulation requires the algorithm development that combines the effective medium and percolation theories. A physically based percolation model is implemented to characterize the effective electrical conductivity of heterogeneous composites by means of the combination of effective medium (EM) and percolation equations with universal exponents. It is shown that the present model correlates well with the experimental electrical resistivity and acoustic emission data. The change in electrical resistivity after impact is compared with test data of a SA-SiC fiber reinforced SiC matrix composite. The predicted damage after impact and the trend of damage volume correlated well with experimental observations of damage shape and reduction in electrical resistance. Thus, an empirical relationship between damage volume and mechanisms and electrical resistance are developed and presented.

Commentary by Dr. Valentin Fuster
2013;():V004T02A005. doi:10.1115/GT2013-94748.

In order to improve the efficiency of electric power generation with gas turbines, the turbine inlet gas temperature needs to be increased. Hence, it is necessary to apply thermal barrier coatings (TBCs) to various hot gas path components. Although TBCs protect the substrate of hot gas path components from high-temperature gas, their thermal resistance degrades over time because of erosion and sintering of the topcoat. When the thermal resistance of TBCs degrades, the surface temperature of the substrate becomes higher, and this temperature increase affects the durability of the hot gas path components. Therefore, to understand the performance of serviced TBCs, the thermal resistance of TBCs needs to be examined by the nondestructive testing (NDT) method. This method has already been reported for TBCs applied to a combustion liner. However, recently, TBCs have been applied to gas turbine blades that have complex three-dimensional shapes, and therefore, an NDT method for examining the thermal resistance of TBCs on blades was developed. This method is based on active thermography using carbon dioxide laser heating and surface temperature measurement of the topcoat by using an infrared camera. The thermal resistance of TBCs is calculated from the topcoat surface temperature when the laser beam heats the surface. In this study, the developed method was applied to a cylindrical TBC sample that simulated curvature on the suction side of a blade, and the results showed the appropriate laser heating condition for this method. Under the appropriate condition, this method could also examine the thermal resistance of TBCs present at 70% of the height of the blade. With these results, this method could determine the thermal resistance within an error range of 4%, as compared to destructive testing.

Commentary by Dr. Valentin Fuster
2013;():V004T02A006. doi:10.1115/GT2013-95054.

Ceramic thermal barrier coatings (TBCs), attributed to their inherent brittle nature, are highly susceptible to damage by impacting foreign particles when the impacting kinetic energy exceeds certain limits. The damage is termed foreign object damage (FOD) in related turbine components and results in various issues/problems to coatings as well as to substrates from delamination to spallation to cracking to catastrophic failure depending on the severity of impact. The FOD testing was performed using a ballistic impact gun for turbine airfoil components coated with 7% yittria stabilized zirconia (7YSZ) by electron beam physical vapor deposit (EB-PVD). A range of impact velocities up to Mach 1 was applied with three different projectile materials of steel, silicon nitride, and glass balls. The damage was assessed and characterized in terms of impact velocity, projectile material, and remaining life of turbine components. An energy-balance approach was made to develop a model to predict delamination of the TBCs upon impact.

Commentary by Dr. Valentin Fuster
2013;():V004T02A007. doi:10.1115/GT2013-95104.

Issues associated with replacing conventional metallic vanes with Ceramic Matrix Composite(CMC) vanes in the first stage of the High Pressure Turbine(HPT) are explored. CMC materials have higher temperature capability than conventional HPT vanes, and less vane cooling is required. The benefits of less vane coolant are less NOx production and improved vane efficiency. Comparisons between CMC and metal vanes are made at current rotor inlet temperatures and at an vane inlet pressure of 50 atm.. CMC materials have directionally dependent strength characteristics, and vane designs must accommodate these characteristics. The benefits of reduced NOx and improved cycle efficiency obtainable from using CMC vanes. are quantified Results are given for vane shapes made of a two dimensional CMC weave. Stress components due to thermal and pressure loads are shown for all configurations. The effects on stresses of: (1) a rib connecting vane pressure and suction surfaces; (2) variation in wall thickness; and (3) trailing edge region cooling options are discussed. The approach used to obtain vane temperature distributions is discussed. Film cooling and trailing edge ejection were required to avoid excessive vane material temperature gradients. Stresses due to temperature gradients are sometimes compressive in regions where pressure loads result in high tensile stresses.

Commentary by Dr. Valentin Fuster
2013;():V004T02A008. doi:10.1115/GT2013-95492.

This paper discusses the potential of using porous ceramic lining as insulating material in combustion chambers with respect to their sound absorbent ability to suppress thermoacoustic instabilities. For this purpose a combustion chamber test rig was developed and different types of ceramic linings were tested. The examined range of power was between 40 and 250 kW and the air-propane equivalence ratio was between 1.2 and 2.0. The overall sound pressure level and frequency domain of a lean premixed swirl stabilized and piloted burner are presented. The resonance frequencies and sound pressure levels are obtained and compared for the different combustion chamber linings. The results show a significant decrease in overall sound pressure level by up to 23.5 dB for sound absorbent lining in comparison to the common sound reflecting combustion chamber lining. In summary, sound absorbent ceramic combustion chamber lining can contribute to improve the stability of lean premixed gas turbines.

Commentary by Dr. Valentin Fuster
2013;():V004T02A009. doi:10.1115/GT2013-95526.

The influence, and interdependence, of water vapor and Na2SO4–50 mol% NaCl on the oxidation of a NiCoCrAlY coating and a thermal barrier coating (TBC) were studied at 750 °C. Water vapor was found to have a negligible effect on oxide composition, but influenced the oxide morphology on the NiCoCrAlY coating. Na2SO4–50 mol% NaCl deposits on the coatings influenced oxide composition, most notably by the promotion of a Y rich phase. The effect of Na2SO4–50 mol% NaCl deposits was also evident for the TBC coated specimen, where the formed metal/ceramic interface oxide was affected by salt reaching the interface by penetration of the zirconia TBC.

Commentary by Dr. Valentin Fuster
2013;():V004T02A010. doi:10.1115/GT2013-95638.

Implementation of ceramic matrix composites (CMCs) in jet engine applications necessitates the understanding of high velocity impact behavior. To this end, various melt-infiltrated SiC/SiC composites were impacted at room temperature at ∼350 m/s with different support systems and tensile tested to failure. Non-Destructive techniques including electrical resistance (ER) and flash thermography were used to examine the specimen pre and post impact. Some specimens were then post-tested in order to assess retained properties. For post tested specimens acoustic emission was used to monitor damage accumulation during the post test and leading up to ultimate failure. Microscopy was performed to correlate damage with impact and post-impact applied stress. The properties of the impacted specimens were assessed based on relevant damage zones. The results are also compared with similar studies performed on similar composites with stress-concentrators such as holes or notches and post-impact specimens tested in bending.

Commentary by Dr. Valentin Fuster
2013;():V004T02A011. doi:10.1115/GT2013-96031.

Development of an ultra-high temperature sensor advocates numerous applications in a variety of diverse fields. Combustion turbine engine advancements are predominately the benefactors of high temperature measurement capabilities; founded upon the principle of higher combustion reaction efficiency. The interior combustion chamber of a gas turbine is an extremely hostile environment for any typical material, especially a measurement component. Implementing the conductive properties and high temperature stability of a polymer derived ceramic (PDC) offers a solution to this predicament. Complementing the virtuous mechanical properties of the unique ceramic is micro-machinability and tunable electric characteristics established from the precursor compounds. The thermo-electric qualities of the PDC prepare formulation of a relationship between the changing temperatures of the research environment with respect to the internal resistance of the ceramic. An elected measurement system will actively monitor a PDC sensory circuit as well as reference thermocouple temperature. Series of response experiments were performed to characterize the functionality of the sensor within the high temperature environment.

Commentary by Dr. Valentin Fuster

Concentrating Solar Power Plants

2013;():V004T05A001. doi:10.1115/GT2013-94046.

The construction of the first generation of commercial hybrid solar gas-turbine power plants will present the designer with a large number of choices. To assist decision making, a thermoeconomic study has been performed for three different power plant configurations, namely simple- and combined-cycles as well as simple-cycle with the addition of thermal energy storage. Multi-objective optimization has been used to identify Pareto-optimal designs and highlight the trade-offs between minimizing investment costs and minimizing specific CO2 emissions. The solar hybrid combined-cycle plant provides a 60% reduction in electricity cost compared to parabolic trough power plants at annual solar shares up to 20%. The storage integrated designs can achieve much higher solar shares and provide a 7–13% reduction in electricity costs at annual solar shares up to 90%. At the same time, the water consumption of the solar gas-turbine systems is significantly lower than conventional steam-cycle based solar power plants.

Commentary by Dr. Valentin Fuster
2013;():V004T05A002. doi:10.1115/GT2013-94271.

Hybrid solar micro gas-turbines are a promising technology for supplying controllable low-carbon electricity in off-grid regions. A thermoeconomic model of three different hybrid micro gas-turbine power plant layouts has been developed, allowing their environmental and economic performance to be analyzed. In terms of receiver design, it was shown that the pressure drop is a key criterion. However, for recuperated layouts the combined pressure drop of the recuperator and receiver is more important. The internally-fired recuperated micro gas-turbine was shown to be the most promising solution of the three configurations evaluated, in terms of both electricity costs and carbon emissions. Compared to competing diesel generators, the electricity costs from hybrid solar units are between 10% and 43% lower, while specific CO2 emissions are reduced by 20–35%.

Commentary by Dr. Valentin Fuster
2013;():V004T05A003. doi:10.1115/GT2013-94308.

A thermoeconomic model of a novel hybrid solar gas-turbine power plant with an air-based bottoming cycle has been developed, allowing its thermodynamic, economic, and environmental performance to be analyzed. Multi-objective optimization has been performed to identify the trade-off between two conflicting objectives: minimum capital cost and minimum specific CO2 emissions. In-depth thermoeconomic analysis reveals that the additional bottoming cycle significantly reduces both the levelized cost of electricity and the environmental impact of the power plant (in terms of CO2 emissions and water consumption) when compared to a simple gas-turbine power plant without bottoming cycle. Overall, the novel concept appears to be a promising solution for sustainable power generation, especially in water-scarce areas.

Commentary by Dr. Valentin Fuster
2013;():V004T05A004. doi:10.1115/GT2013-94562.

The operation of steam turbine units in solar thermal power plants is very different than in conventional base-load plants. Due to the variability of the solar resource, much higher frequencies of plant start-ups are encountered. This study provides an insight to the influence of thermal energy storage integration on the typical cycling operation of solar thermal power plants. It is demonstrated that the integration of storage leads to significant reductions in the annual number of turbine starts and is thus beneficial to the turbine lifetime. At the same time, the effects of storage integration on the electricity costs are analyzed to ensure that the designs remain economically competitive. Large storage capacities, can allow the plant to be shifted from a daily starting regime to one where less than 20 plant starts occur annually. Additionally, the concept of equivalent operating hours is used to further analyze the direct impact of storage integration on the maintenance planning of the turbine units.

Commentary by Dr. Valentin Fuster
2013;():V004T05A005. doi:10.1115/GT2013-94713.

Concentrating Solar Power (CSP) technologies are considered to provide a significant contribution for the electric power production in the future. Different kinds of CSP technologies are presently in operation or under development, e.g. parabolic troughs, central receivers, solar dish systems and Fresnel reflectors. In such applications, electricity is produced by thermal energy conversion cycles. For high MW-class CSP applications usually water/steam cycles (Rankine cycles) are used. Alternative technologies, especially for central receiver applications, are open and closed gas turbine cycles (Brayton cycles), where higher receiver fluid outlet temperatures can be applied. Therefore, there is the potential of higher cycle efficiencies and the advantage of reduced water consumption. The paper presents the results for design considerations to improve a gas turbine cycle of a 2 MWel class industrial gas turbine for solar-thermal application, where solar heat is fed in by a central receiver technology. The reference process is improved significantly by application of an intercooler between the two radial compressor stages and a recuperator, which recovers heat from the exhaust gases to the compressed air before the air is further pre-heated by the solar receiver. Hybrid operation of the gas turbine is considered. In order to further improve the overall cycle efficiency, the combined operation of the gas turbine and an Organic Rankine Cycle is investigated. The ORC can be coupled to the solar-thermal gas turbine cycle at the intercooler and after the recuperator. Therefore, waste heat from different cycle positions can be transferred to the ORC for additional production of electricity. The investigations have been performed by application of improved thermodynamic and process analysis tools, which consider real gas behavior of fluids and a huge number of organic fluids for application in ORCs. The results show that by choice of a suitable organic fluid the waste heat recovery can be further improved for the investigated gas turbine cycle. The major result of the study is that by combined operation of the solar thermal gas turbine and the ORC, the combined cycle efficiency is approximately 4%-points higher than in the solar-thermal gas turbine cycle.

Commentary by Dr. Valentin Fuster
2013;():V004T05A006. doi:10.1115/GT2013-94939.

A NiCrAl-type foil (alloy 214) was selected for evaluation for heat exchanger applications for a concentrated solar power (CSP) system. Due to the formation of a protective alumina surface oxide, this class of alloys can operate at higher temperatures than conventional stainless steels or even Ni-base alloys, such as alloy 625. Laboratory testing is being conducted at 1000° and 1050°C in dry air using 10 h thermal cycles in order to simulate the CSP duty cycle at a high temperature to accelerate the degradation process. Mass change data showed indications of degradation of the foils with exposures up to 8,000 h. Foil specimens also were stopped after 2,400 h to measure the loss of Al in the foil as a method to predict lifetime. Previous lifetime modeling results for 1h cycles in air with 10%H2O provided an initial basis to predict lifetime for this material to >100,000 h operating times as a function of foil thickness and exposure temperature for this application.

Commentary by Dr. Valentin Fuster
2013;():V004T05A007. doi:10.1115/GT2013-94990.

Concentrating Solar Power (CSP) plants often use Rankine cycles operated with water/steam as energy conversion cycles. Since the solar central receiver technology could provide receiver fluid outlet temperatures higher than 900°C, open and closed gas turbine technologies become a promising alternative. Closed solar Brayton cycles operating with appropriate fluids can reach similar or higher thermal efficiencies than water/steam Rankine cycles but have the advantage of less consumption of fresh water.

This paper presents the results of a comparative thermodynamic and process study of closed solar thermal Brayton cycles operated with Helium or Argon as working fluids. The main components of the cycles are two axial compressors with an intercooler, a recuperator and one axial turbine. The solar heat is fed in by a central receiver technology. It is assumed that the transferred heat to the cycles is constant and the turbine inlet temperature is 900°C.

A first one-dimensional design approach for both cycles is performed based on the results of the thermodynamic considerations. The major parameters like stage types, number of stages, rotational speed, etc. are determined and discussed.

The thermodynamic and process investigation results for the described closed Brayton cycles show that thermal efficiencies over 46% can be established for both fluids. The design considerations show that both cycles are feasible, but with respect to design dimensions the Argon based cycle can be built up with fewer stages and more compact, if compared to the Helium cycle.

Commentary by Dr. Valentin Fuster
2013;():V004T05A008. doi:10.1115/GT2013-95483.

The present paper investigates two different Solarized Combined Cycle layout configurations. In the first scheme, a solarized gas turbine is coupled to a solar tower. Pressurized air at compressor exit is sent to the solar tower receiver before entering the GT combustor. Here temperature is increased up to the nominal turbine inlet value through natural gas combustion. In the second CC layout, solar energy is collected by line focusing parabolic trough collectors and used to produce superheated steam in addition to the one generated in the heat recovery boiler. The goal of the paper is to compare the thermodynamic performance of these CSP technologies when working under realistic operating conditions. Commercial software and in-house computer codes were combined together to predict CSP plant performance both on design and off-design conditions. Plant simulations have shown the beneficial effect of introducing solar energy at high temperature in the Joule-Brayton cycle and the drawback in terms of GT performance penalization due to solarization. Results of yearly simulations on a one hour basis for the two considered plant configurations are presented and discussed. Main thermodynamic parameters such temperatures, pressure levels, air and steam flow rates are reported for two representative days.

Commentary by Dr. Valentin Fuster

Controls, Diagnostics and Instrumentation

2013;():V004T06A001. doi:10.1115/GT2013-94104.

Gas turbine efficiency can be improved with tighter turbine tip clearances. An approach being developed by engine manufacturers deploys active tip clearance monitoring where the turbine casing diameter is actively controlled in-service either mechanically or thermally. Typically current engines operate at about 1% clearance of blade span. With active control this could potentially be reduced significantly.

Ideally active tip clearance control requires closed loop feedback measurements to maintain very small clearances without the risk of blade tip contact with the casing liner. Therefore reliable and robust sensors systems are required that can operate at the elevated temperatures found in modern gas turbines. Currently there are limited sensor systems available that can operate at these temperatures and survive typical sensor life requirements of many thousands of hours.

This study details development of a high temperature eddy current sensor system for hot section applications. The investigation encompasses development and validation of an integrated sensor design to provide tip clearance measurements. The sensor is designed to withstand temperatures of order 1500 to 1600K. Test facilities used to validate the system include a RB168 Mk 101 Spey engine and a Rolls-Royce VIPER engine. The turbine casings of both engines were modified to fit sensors directly above the rotor. The accuracy of the system was validated in a high speed rotor test facility with engine representative blading. Accuracy of the eddy current sensor was compared and validated against a dynamic laser micrometer system.

Commentary by Dr. Valentin Fuster
2013;():V004T06A002. doi:10.1115/GT2013-94179.

Active flow control is a powerful option to ensure secure operation and enhancement of the performance of axial compressors. To achieve these goals for aerodynamically highly loaded compressor blade profiles even under disturbed conditions, the magnitude of the actuation needs to be adjusted by a closed-loop controller. To this end, sensors must be placed at some meaningful positions at the surface of the blades giving information about the flow situation inside the passages. The sensor information can then lead to surrogate control variables to close the loop. Often, good sensor positions are unknown initially and therefore chosen naively or experience-driven. To obtain more informative surrogate control variables, a different approach is chosen here. Starting with a highly instrumented blade inside a linear stator cascade, featuring 16 pressure gauges in an area which is suspected to lead to high information content with respect to detrimental flow separations at the sidewalls, a Principal Component Analysis is done. The principal components provide valuable information about where and how intensively the flow is influenced by the actuation. This is validated by comparison with the results of oil flow visualizations and wake measurements. The goal is to find a linear combination of as few sensors as possible to provide a meaningful input for the closed-loop controller. As experiments are conducted up to Ma = 0.8, the signal-to-noise ratio becomes a critical issue. For this reason, specifically weighted data are introduced here. A linear combination of sensor data is obtained, describing the main effects of the actuation with an almost linear mapping. For the given set of sensors, that linear combination achieves a maximum signal-to-noise ratio, which makes it well suited as a control variable. The practical usefulness of the control variable within a robust ℋ-flow controller is verified in experiments in a high speed stator cascade.

Commentary by Dr. Valentin Fuster
2013;():V004T06A003. doi:10.1115/GT2013-94203.

Vibration excursion in turbomachinery is troublesome, especially when approaching or exceeding a trip level. Understanding of its root-cause is extremely crucial for taking appropriate actions and resolving the issue. Rubs are certainly among the most common malfunctions that cause vibration excursion. This paper discusses how to diagnose rubs that typically occur in turbomachinery based on vibration data. These include rubs occurring in both steady-state and transient conditions. Selection and interpretation of vibration data plots such as trend, polar, Bode, orbit, and waterfall are illustrated that pinpoint rubbing and resulted shaft bow symptoms. All data presented have been obtained from real machines where rubs occurred. Mainly case studies are presented in this paper. The presented cases and concluded diagnostic rules using vibration data plots will help practicing engineers as well as enhance diagnostic tools.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2013;():V004T06A004. doi:10.1115/GT2013-94216.

This paper presents the results of applying a data-driven condition-based monitoring system for the fault detection of a boiler leakage in a Combined Cycle Power Plant (CCPP). An auto associative kernel regression model is developed using normal process data and tested with faulted data to determine the earliest warning of the boiler leakage. Automatic variable grouping, which uses the linear correlations among the available thirty sensors, is employed to obtain optimal groupings to be used in model development. Several models were developed, optimized and compared. A logic test was used for fault detection and this test produced alarms in the region were the leak was later confirmed to have occurred. Comparison of these results with those of a physics-based analysis also confirmed the accuracy of the models in the early detection of the leakage.

Commentary by Dr. Valentin Fuster
2013;():V004T06A005. doi:10.1115/GT2013-94239.

The heavy duty gas turbines evolution led to higher combined cycle efficiencies. Thus, more complex heat recovery steam generators were developed in order to maximize the use of that energy potential. Therefore, computational models capable to predict the operational conditions of the equipment may be needed in order to analyze the system behavior for different situations. This article describes a computational model able to simulate the off-design behavior of a heat recovery steam generator (HRSG) operating in a combined cycle power plant. The model was developed so that it can be used in both model-based diagnostics systems and performance evaluation systems. Each heat exchanger inside the HRSG was designed individually and arranged according to the analyzed equipment. The computer code’s architecture was built in such a way that it can be easily changed, allowing the analysis of other HRSG’s configurations with simple structural changes, given the program’s modularity. In order to deal with the lack of details of the power plant equipment, which means not enough geometrical information of each heat exchanger, a generic algorithm tool was used to calibrate the heat exchangers models using only the measured data of the power plant SCADA. The developed program was validated against operational data from a real plant and showed satisfactory results, confirming the robustness of this model.

Commentary by Dr. Valentin Fuster
2013;():V004T06A006. doi:10.1115/GT2013-94382.

The effects of tip shape on the Reynolds number sensitivity of a seven hole pressure probe are studied over a range of flows associated with practical use of turbomachinery. It is shown that at low flow angles, the response of a conical or hemispherical tipped probe is independent of Reynolds number above Re = 3000, and at high flow angles, Re = 6000. Despite there not being a discernable difference in the average error in flow properties at different Reynolds numbers between the two tip shapes, it is shown that the hemispherical tip is preferred because the pressure distributions around the tip are more consistent.

Commentary by Dr. Valentin Fuster
2013;():V004T06A007. doi:10.1115/GT2013-94464.

This paper presents a methodology for developing a control oriented analytical linear model of a turbofan engine at both equilibrium and non-equilibrium conditions. This scheme provides improved accuracy over the commonly used linearization method based on numerical perturbation. Linear coefficients are obtained by evaluating at current conditions analytical expressions which result from differentiation of simplified nonlinear expressions. Residualization of the fast dynamics states are utilized since the fast dynamics are outside of the primary control bandwidth. Analytical expressions based on the physics of the aerothermodynamic processes of a gas turbine engine facilitate a systematic approach to the analysis and synthesis of model based controllers. In addition, the use of analytical expressions reduces the computational effort, enabling linearization in real time at both equilibrium and non-equilibrium conditions to enable more accurate capture of system dynamics during aggressive transient maneuvers. The methodology is formulated and applied to a separate flow twin spool turbofan engine model in the Numerical Propulsion System Simulation (NPSS) platform. The derived linear model is validated against the full nonlinear engine model.

Topics: Engines , Turbofans
Commentary by Dr. Valentin Fuster
2013;():V004T06A008. doi:10.1115/GT2013-94496.

This paper addresses the problem of estimation of unmeasured gas turbine engine variables using statistical analysis of measured data. Possible changes of an engine health condition and lack of information about these changes caused by limited instrumentation are taken into account. Engine thrust is under consideration as one of the most important unmeasured parameters. Two common methods of aircraft gas turbine engine (GTE) thrust monitoring and their errors due to health condition changes are analyzed. Additionally, two mathematical techniques that allow reducing in-flight thrust estimation errors in the case of GTE deterioration are suggested and verified in the paper. They are a ridge trace and a principal component analysis.

A turbofan engine has been chosen as a test case. The engine has five measured variables and 23 health parameters to describe its health condition. Measurement errors are simulated using a generator of random numbers with the normal distribution. The engine is presented in calculations by its nonlinear component level model (CLM). Results of the comparison of thrust estimates computed by the CLM and the proposed techniques confirm accuracy of the techniques. The regression model on principal components has demonstrated the highest accuracy.

Commentary by Dr. Valentin Fuster
2013;():V004T06A009. doi:10.1115/GT2013-94629.

Predicting the vibratory response of structures with complex geometry can be challenging especially when their properties (geometry and material properties) are not known accurately. These structures can suffer also from high modal density, which can result in small changes in structural properties creating large changes in the resonant response. To address this issue, structural properties could be accurately identified, or the structural response could be experimentally measured. Both these approaches require collecting measurements of higher order vibration modes which have complicated shape. Consequently, high-accuracy positioning of laser beams is necessary for vibrometers based on laser Doppler velocimetry. This paper presents a methodology to address this challenge. The architecture involves a single-point vibrometer, a motion controller, translating/rotating stages, and special application software for alignment and edge detection. A key novelty of this technology is that the beam of the vibrometer is used for both detecting the edges and for measuring the vibration. Using a motion controller, the system can automatically place/scan and measure the surface of the structure with a positioning resolution of 1 μm. Experimental results are provided to demonstrate the new technique.

Commentary by Dr. Valentin Fuster
2013;():V004T06A010. doi:10.1115/GT2013-94706.

An on demand oil system, based on electrically driven lube and scavenge pumps, for use in gas turbine engines has been developed. The need to optimize gas turbine engine performance, coupled with ‘electrification’ of aircraft systems, as on the Lockheed F35 and Boeing 787 in order to maximize efficiency and flexibility, created an opportunity to develop a ‘smart’ electrically driven lubrication system for gas turbine engines. Spytek’s electric oil system, developed for use on its 400lbt ATG-2 engine platform, ascertains the operating condition of the gas turbine engine, including speed, pressure, bearing temperatures and determines the amount of lubrication required for each bearing zone. The system has the benefit of better thermal control of engine bearings, lower system weight and power use, with flexibility in the placement of the system on the engine/airframe combination. The system has been successfully demonstrated on the Spytek Aerospace ATG-2/J304 gas turbine engine series.

Major areas addressed in the development of the system were the selection of reliable, gas turbine engine compatible feed and scavenge pumps, control systems sensoring and feedback, variable feed of oil to the individual sump wells, as well as systems durability and operating parameters. Various gas turbine engine platforms can require altered oil system duty cycles, including pre-oiling or post run down-oiling, high flow oil conditions, features not readily available in traditional mechanical systems but easily implemented using the Spytek on-demand oil system.

In the project effort, evaluation of the existing prototype system was used as a system design baseline. Data on pump wear, filter performance and oil supply degradation was available and used in refining the oil system design. The ATG-2 system was modified to take advantage of a full proportional integral derivative controlled oil system with system demonstrations made on a gas turbine engine, demonstrating oil supply on demand capability and full bearing thermal management system control.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2013;():V004T06A011. doi:10.1115/GT2013-94831.

This paper presents and validates a physics-based, dynamic model of a gas turbine. The model is an extension of that proposed by Badmus et al. [1], such that representation of a complete gas turbine is achieved. It includes new models of several gas turbine components, in particular the turbine and compressor, and also applies a well known method for prescribing boundary conditions [10] to the gas path.

This model first uses data from a previously published, static model of the same gas turbine to determine this dynamic model’s many so-called ‘forcing terms’. A least-squares optimisation is then undertaken to estimate the shaft inertia and the thermal inertia of system components using transient test data. Importantly, these optimised results are all close to physically reasonable estimates. Further, they show that the shaft dynamics are only significant for a short period at the start of most transients, after which the dynamic effects of thermal storage are dominant.

The complete gas turbine model is then validated against transient test data. Whilst the simulated traces demonstrate some steady-state error arising from the static model [12], the overall system dynamics appear to be captured well. Since steady-state error can be integrated out in a control system, this suggests that the proposed dynamic model is appropriate for use in a model-based, gas turbine controller.

Commentary by Dr. Valentin Fuster
2013;():V004T06A012. doi:10.1115/GT2013-94910.

Artificial intelligent technologies are being investigated for development of advanced adaptation and reconfiguration algorithms for turbine engine distributed control systems. Adding adaptation and reconfiguration feature to the control systems is expected to improve engine performance and provide more efficient aircraft operations. The benefits of transitioning from the existing centralized supervisory control, the Full Authority Digital Electronic Control (FADEC), of turbine engines to distributed control architecture have been well articulated in the literature. The major benefits are summarized as; weight reduction, cost saving, and damage tolerant turbine engines. However, consideration of advanced intelligent technologies in the design and operation of distributed control systems has been a challenging task and requires further investigation. This paper describes research activities to address the above stated challenge leading to fully reconfigurable distributed control systems for turbine engines of the future aircrafts. The goal of the research work is to accelerate the development and implementation of disturbed control systems in aircrafts propulsion controls and its integration with distributed diagnostics and prognostics algorithms. This will be achieved by means of using artificial intelligent technologies to design adaptation and reconfiguration algorithms and integrate it with a set of engine decentralized controllers. Fuzzy inference concept will be used to develop and implement the proposed adaptation and reconfiguration algorithms. Finally, the integrated reconfiguration algorithms with the control system will be tested and verified on publicly available turbine engine simulation software.

Commentary by Dr. Valentin Fuster
2013;():V004T06A013. doi:10.1115/GT2013-95049.

The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation sector. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. This work focuses on developing an accurate and reliable algorithm for detecting the accretion of ice in the low pressure compressor of a generic 40,000 lbf thrust class engine. The algorithm uses only the two shaft speed sensors and works regardless of engine age, operating condition, and power level. In a 10,000-case Monte Carlo simulation, the detection approach was found to have excellent capability at determining ice accretion from sensor noise with detection occurring when ice blocks an average of 6.8% of the low pressure compressor area. Finally, an initial study highlights a potential mitigation strategy that uses the existing engine actuators to raise the temperature in the low pressure compressor in an effort to reduce the rate at which ice accretes.

Commentary by Dr. Valentin Fuster
2013;():V004T06A014. doi:10.1115/GT2013-95077.

Recent technology reviews have identified the need for objective assessments of aircraft engine health management (EHM) technologies. To help address this issue, a gas path diagnostic benchmark problem has been created and made publicly available. This software tool, referred to as the Propulsion Diagnostic Method Evaluation Strategy (ProDiMES), has been constructed based on feedback provided by the aircraft EHM community. It provides a standard benchmark problem enabling users to develop, evaluate and compare diagnostic methods. This paper will present an overview of ProDiMES along with a description of four gas path diagnostic methods developed and applied to the problem. These methods, which include analytical and empirical diagnostic techniques, will be described and associated blind-test-case metric results will be presented and compared. Lessons learned along with recommendations for improving the public benchmarking processes will also be presented and discussed.

Commentary by Dr. Valentin Fuster
2013;():V004T06A015. doi:10.1115/GT2013-95090.

Test and evaluation are critical to any product development program. The validation of engine sensor products is particularly challenging since the test engine required for validation can range in value from thousands to millions of dollars, costing much more than the sensor product itself. As a result, significant sensor testing and validation is required by an engine owner prior to on-engine testing. To support our development activities and to facilitate test validation acceptance, we have created a test and evaluation platform for gas turbine sensors that will allow us to test developmental sensors in an engine-like environment without risking the possibility of engine damage. Driven by the core exhaust of a JT15-D engine, the Dynamic Rotor Research Rig (DR3) test and evaluation platform provides a test capability that is highly representative of the high temperatures, vibrations, gasses, fluids and overall gas turbine engine environment, while providing the means to easily add and replace sensors, add and test custom rotors, control temperature and rotor speeds, and to not risk engine health during test activities.

Here we will discuss our sensor testing goals and how they fed into the operational goals and design considerations for the DR3. Early design concepts and the ultimate approach we took with the DR3 design will be explored, along with the candidate test rig component and subassembly fabrication processes that we evaluated and ultimately selected for use. We will review the manufacturing issues that we encountered during the construction phase of the DR3 and overview the commissioning of the DR3, problems that we discovered during start up and how we solved them.

Included will be the results of initial turbine blade clearance and blade tip timing sensor testing performed on the DR3 and an evaluation of the DR3 performance, including temperature and speed control of the test rig and other characterization of the operating regime of the rig. Finally, we will present future plans to upgrade the DR3 rig to support future high temperature sensor and blade health monitoring development activities.

Topics: Engines , Design
Commentary by Dr. Valentin Fuster
2013;():V004T06A016. doi:10.1115/GT2013-95105.

LibertyWorks™ (Rolls-Royce North American Technologies Inc.) is developing an integrated environment for design, development, testing, and integration of current and future decentralized gas turbine engine control systems. This paper serves as a mid-project status update to solicit recommendations from industry and academia on what might be done to make it better, and to give the community a preview. Identified as the Decentralized Engine Control System Simulator (DECSS), this system has the capabilities to support flexible, decentralized control system architectures containing both simulated and physical hardware-in-the-loop control components. Neither the DECSS nor the project developing the DECSS will make a selection of a preferred control system architecture/design method, nor a preferred communication architecture/protocol, but instead will provide a flexible environment for future users to rapidly evaluate potential solutions in a real-time environment with hardware in the loop. This paper describes the DECSS functions, capabilities, organization and how it will be used as a NASA asset for future engine control system development.

Commentary by Dr. Valentin Fuster
2013;():V004T06A017. doi:10.1115/GT2013-95118.

Turbine engines are highly complex mechanical systems that are becoming increasingly dependent on control technologies to achieve system performance and safety metrics. However, the contribution of controls to these measurable system objectives is difficult to quantify due to a lack of tools capable of informing the decision makers. This shortcoming hinders technology insertion in the engine design process. NASA Glenn Research Center is developing a Hardware-in-the-Loop (HIL) platform and analysis tool set that will serve as a focal point for new control technologies, especially those related to the hardware development and integration of distributed engine control. The HIL platform is intended to enable rapid and detailed evaluation of new engine control applications, from conceptual design through hardware development, in order to quantify their impact on engine systems. This paper discusses the complex interactions of the control system, within the context of the larger engine system, and how new control technologies are changing that paradigm. The conceptual design of the new HIL platform is then described as a primary tool to address those interactions and how it will help feed the insertion of new technologies into future engine systems.

Commentary by Dr. Valentin Fuster
2013;():V004T06A018. doi:10.1115/GT2013-95152.

Siemens Energy, Inc. has been investigating the potential of a new approach to measuring the process gas temperature leaving the turbine of their heavy industrial gas turbine engines using an acoustic pyrometer system. This system measures the bulk temperature crossing a plane behinds the last row of turbine blades and is a non-intrusive measurement. It has the potential to replace the current intrusive multiple point measurement sensor arrays for both engine control and performance evaluation. The acoustic pyrometer is a device that measures the transit time of an acoustic pulse across the exhaust duct of the engine. An estimate of the temperature of the process fluid can be made from the transit time. Multiple passes may be made at various radial positions to improve the measurement. The gas turbine exhaust is a challenging environment for acoustic temperature measurement where there can be significant temperature stratification and high velocity. Previous applications of acoustic pyrometers to measure process gas temperature in power plants have been confined to applications such as boilers where rapid temperature changes are not expected and fluid velocity patterns are well known. The present study describes the results of acoustic pyrometer testing in an operating gas turbine engine under load using an active acoustic pyrometer system containing eight sets of transmitters and receivers, all external to the turbine exhaust flow path. This active method technology is based on the temperature dependence of the isentropic speed of sound from the simple ideal gas assumptions. Sound transmitters and receivers are mounted around the exhaust duct to measure the speed of sound. Very sophisticated topographical mapping techniques have been developed to extract temperature distribution from using any where from 2 to 8 sensors with up to 24 paths and 400 points. Cross correlation of sensor results to obtain topographical mapping of gas isotherms in a plane in full engine field tests have been conducted to prove the feasible of this technology on a gas turbine engine. The initial installation of the active acoustic pyrometer system in an engine exhaust was accomplished in 2009. All the tests indicate that the steady state measurements of the acoustic pyrometer system fall within 10C of the measured exhaust thermocouple data. An additional installation on a different model engine was subsequently made and data have been gathered and analyzed. Results of these tests are presented and future evaluation options discussed.

Commentary by Dr. Valentin Fuster
2013;():V004T06A019. doi:10.1115/GT2013-95198.

Efficiency of gas turbine monitoring systems primarily depends on the accuracy of employed algorithms, in particular, pattern recognition techniques to diagnose gas path faults. In investigations many techniques were applied to recognize gas path faults, but recommendations on selecting the best technique for real monitoring systems are still insufficient and often contradictory.

In our previous works, three recognition techniques were compared under different conditions of gas turbine diagnosis. The comparative analysis has shown that all these techniques yield practically the same accuracy for each comparison case.

The present contribution considers a new recognition technique, Probabilistic Neural Network (PNN), comparing it with the techniques previously examined. The results for all comparison cases show that the PNN is not practically inferior to the other techniques. With this inference, the recommendation is to choose the PNN for real monitoring systems because it has an important advantage of providing confidence estimation for every diagnostic decision made.

Commentary by Dr. Valentin Fuster
2013;():V004T06A020. doi:10.1115/GT2013-95590.

Failures in the gas path of a Gas Turbine will cause a deviation in the measured performance parameters. One of the most important parameters is the Turbine Exit Temperature (TET) and refers to the hot gas temperature at the exhaust of a Gas Turbine (GT). However, TET is not uniform at the turbine outlet and the temperature is therefore sometimes measured at several axial and radial positions. The TET has what can be considered a natural variation, an effect of operation in different ambient and operational conditions which influences the internal flow field. It can be informative on the health status of the GT by monitoring the TET variation during operation, as a number of failures or abnormal operation conditions will affect the TET distribution. A regular way of monitoring the TET is to use the average value from different sensor readings, or compare the highest deviating sensor to the average value of all sensors. However in order to detect anomalies as early as possible deviations from the healthy profile should be detected more finely across the section. In this paper, a data-driven similarity based algorithm called Auto Associative Kernel Regression is applied to the issue of monitoring the TET spread variation on an industrial gas turbine. A case study is supplied to show the practical usefulness of the algorithm to a field failure.

Commentary by Dr. Valentin Fuster
2013;():V004T06A021. doi:10.1115/GT2013-95608.

A unique methodology and test rig was designed to evaluate the degradation of damaged Nozzle Guide Vanes in a transonic annular cascade in the short duration facility at the Royal Military College. A custom test section was designed which featured a novel rotating instrumentation suite. This permitted 360° multi-span traverse measurements downstream of unmodified turbine NGV rings from a Rolls-Royce/Allison A-250 turbo-shaft engine. Downstream total pressure was measured at four span-wise locations on both an undamaged reference and a damaged test article. Three performance metrics were developed in an effort to determine characteristic signatures for common operational damage such as trailing edge bends or cracked trailing edges. The highest average losses were observed in the root area, while the lowest occurred closer to the NGV tips. The results from this study indicated that multiple span-wise traverses were required to detect localized trailing edge damage. Recommendations have been made for future tests, for test rigs and for ideas to develop performance metrics.

Topics: Gas turbines , Nozzles
Commentary by Dr. Valentin Fuster
2013;():V004T06A022. doi:10.1115/GT2013-95727.

Supervision of the performance of an industrial gas turbine is important since it gives valuable information of the process health and makes efficient determination of compressor wash intervals possible. Slowly varying sensor faults can easily be misinterpreted as performance degradations and result in an unnecessary compressor wash. Here, a diagnostic algorithm is carefully combined with non-linear state observers to achieve fault tolerant performance estimation. The proposed approach is evaluated in an experimental case study with six months of measurement data from a gas turbine site. The investigation shows that faults in all gas path instrumentation sensors are detectable and isolable. A key result of the case study is the ability to detect and isolate a slowly varying sensor fault in the discharge temperature sensor after the compressor. The fault is detected and isolated before the wash condition of the compressor is triggered, resulting in fault tolerant estimation of compressor health parameters.

Commentary by Dr. Valentin Fuster
2013;():V004T06A023. doi:10.1115/GT2013-95739.

Gas path analysis (GPA) is an effective method for determination of turbofan component condition from measured performance parameters. GPA is widely applied on engine test rig data to isolate components responsible for performance problems, thereby offering substantial cost saving potential. Additional benefits can be obtained from the application of GPA to on-wing engine data.

This paper describes the experience with model-based GPA on large volumes of on-wing measured performance data. Critical is the minimization of the GPA results uncertainty in order to maintain reliable diagnostics and condition monitoring information. This is especially challenging giving the variable in-flight operating conditions and limited on-wing sensor accuracy. The uncertainty effects can be mitigated by statistical analysis, and filtering and post-processing of the large datasets. By analyzing correlations between measured performance data trends and estimated component condition trends errors can be isolated from the GPA results. The various methods assessed are described and results are demonstrated in a number of case studies on a large turbofan engine fleet.

Commentary by Dr. Valentin Fuster
2013;():V004T06A024. doi:10.1115/GT2013-95780.

H-optimal controllers are designed for a rotor being subject to unbalance excitation and gyroscopic effect. The system possesses two unbalance-induced resonances within its operating range. The presence of gyroscopic effect is challenging for linear time invariant controller design because of the associated dependence of the system dynamics on the rotational frequency of the rotor. Controllers thus have to be robust against deviation of the actual system behavior from the controller design point model.

For vibration control purposes, there are two piezoelectric actuators installed in one of the two supports of the rotor. The signals of four inductive sensors measuring the displacements of the two discs of the rotor are used for controller design.

In this article, H-optimal controllers are designed on the basis of input and output weighting as well as weighting of modal degrees of freedom and modal excitations. It is shown that superior control performance is achieved using modal weighting since a more accurate problem description of rotors excited by unbalance is incorporated in controller design. Results in this article show furthermore that it is possible to design well performing H-optimal controllers for a gyroscopic rotor by means of iterative controller design without taking model uncertainty directly into account via weighting of certain FRFs of the system to be controlled.

Topics: Rotors
Commentary by Dr. Valentin Fuster
2013;():V004T06A025. doi:10.1115/GT2013-95803.

Many existing aircraft engine diagnostic methods are based on linearized engine models. However, the dynamics of aircraft engines are highly nonlinear and rapidly changing. Future engine health management designs will benefit from new methods that are directly based on intrinsic nonlinearities of the engine dynamics. In this paper, a fault detection and isolation (FDI) method is developed for aircraft engines by utilizing nonlinear adaptive estimation and nonlinear observer techniques. Engine sensor faults, actuator faults and component faults are considered under one unified nonlinear framework. The fault diagnosis architecture consists of a fault detection estimator and a bank of nonlinear fault isolation estimators. The fault detection estimator is used for detecting the occurrence of a fault, while the bank of fault isolation estimators is employed to determine the particular fault type or location after fault detection. Each isolation estimator is designed based on the functional structure of a particular fault type under consideration. Specifically, adaptive estimation techniques are used for designing the isolation estimators for engine component faults and actuator faults, while nonlinear observer techniques are used for designing the isolation estimators for sensor faults. The FDI architecture has been integrated with the Commercial Modular Aero-Propulsion System Simulation (C-MAPSS) engine model developed by NASA researchers in recent years. The engine model is a realistic representation of the nonlinear aero thermal dynamics of a 90,000-pound thrust class turbofan engine with high-bypass ratio and a two-spool configuration. Representative simulation results and comparative studies are shown to verify the effectiveness of the nonlinear FDI method.

Commentary by Dr. Valentin Fuster
2013;():V004T06A026. doi:10.1115/GT2013-95922.

The next generation of aircraft will face more challenging demands in both electrical and thermal loads. The larger thermal loads reduce the propulsion system efficiency by demanding bleed air from the main engine compressor or imposing a shaft load on the high or low pressure shaft. The approach adopted to power the thermal management system influences the overall fuel burn of the aircraft for a given mission. To assess these demands and to explore conceptual designs for the electrical and thermal management system, a dynamic vehicle level tip-to-tail (T2T) model has been developed. The T2T model captures and quantifies the energy exchanges throughout the aircraft. The following subsystems of the aircraft are simulated in the T2T model: Air vehicle system, propulsion system, adaptive power thermal management system, fuel thermal management system, electrical system and actuator system. This paper presents trade studies of the impact of various approaches in power take-off from the main engine and control strategies. The trade studies identify different control strategies resulting in significant fuel savings for a given mission profile.

Commentary by Dr. Valentin Fuster
2013;():V004T06A027. doi:10.1115/GT2013-96012.

We develop and describe a stable gain scheduling controller for a gas turbine engine that drives a variable pitch propeller. A stability proof is developed for gain scheduled closed-loop system using global linearization and linear matrix inequality (LMI) techniques. Using convex optimization tools, a single quadratic Lyapunov function is computed for multiple linearizations near equilibrium and non-equilibrium points of the nonlinear closed-loop system. This approach guarantees stability of the closed-loop gas turbine engine system. Simulation results show the developed gain scheduling controller is capable of regulating a turboshaft engine for large thrust commands in a stable fashion with proper tracking performance.

Commentary by Dr. Valentin Fuster
2013;():V004T06A028. doi:10.1115/GT2013-96024.

Accurate static and dynamic pressure measurements provide the feedback needed to advance gas turbine efficiency and reliability as well as improve aircraft design and flight control. During turbine testing and aircraft flight testing, flush mounting pressure transducers at the desired pressure measurement location is not always feasible and recess mounting with connective tubing is often used as an alternative. Resonances in the connective tubing can result in aliasing within pressure scanners even within a narrow bandwidth and especially when higher frequency content DC to ∼125Hz is desired. We present experimental results that investigate tube resonances and attenuation in 1.35mm inner diameter (ID) (used on 0.063in tubulations) and 2.69mm ID (used on 0.125in tubulations) Teflon and Nylon tubing at various lengths. We utilize a novel dynamic pressure generator, capable of creating large changes in air pressure (<1psi to 10psi, <6.8kPa to 68.9kPa), to determine the frequency response of such tubing from ∼1Hz to 2,800Hz. We further compare these experimental results to established analytical models for propagation of pressure disturbances in narrow tubes. While significant theoretical and experimental work relating to the frequency response of connective tubing or transmission lines has been published, there is limited literature presenting experimental frequency response data with air as the media in elastic tubing. In addition, little progress has been made in addressing the issue of tubing-related aliasing within pressure scanners, as the low sampling rate in scanners often makes post-processing antialiasing filters ineffective.

The experimental results and analytical models presented herein can be used as a guideline to prevent aliasing and signal distortion by guiding the proper design of pressure transmission systems, resulting in accurate static and dynamic pressure measurements with pressure scanners. The data presented here should serve as a reference to instrumentation engineers so that they can make higher frequency measurements (up to ∼125Hz, currently) and are able to quantify the expected pressure transmission line (tube) attenuation and know if aliasing will be a concern. This information will give engineers greater measurement capability when using pressure scanners to make static and dynamic pressure measurements.

Commentary by Dr. Valentin Fuster

Education

2013;():V004T08A001. doi:10.1115/GT2013-94149.

Three-dimensional Model-Based Engineering (MBE) along with Quality Information Framework (QIF) is an approach to product design, manufacturing, and support where a digital three-dimensional representation of the product serves as the normative source for information communicated throughout the product’s lifecycle and supply chain. MBE simplifies data management and provides a more powerful communication medium than 2D-based environments. This is not just using a model for reference or a visual aid. The model will be the definition for the parts being manufactured, inspected, and built into full engines. The use of two-dimensional prints will be outdated and a culture change will be needed to embrace this change. Many organizations are implementing MBE and are using this technology to produce aerospace products. Manufacturing and inspection functions are dependent on the models from cradle to grave of the product lifecycle. These smart models will have all of the necessary dimensional metrology interoperability, GD&T encoded and product manufacturing information (PMI) data all in a standardized format associated within the model. This will allow for a model that has less errors, more functionality with manufacturing and inspection systems. The information included in the Model Based Definition (MBD) will be part of the QIF.

The QIF fully defines quality measurement plans, measurement results, measurement rules, measurement resources, and results analysis. This combined with the PMI for manufacturing will provide a comprehensive MBD that can be used for all of the manufacturing process in the lifecycle of the product.

The culture will need to progress from two-dimensional paper prints to smart three-dimensional models that are rich with data. These models will drive the process and be the final word for part acceptance; paper prints will not be needed or produced. These types of models will drive almost all of the military’s new designs and if the organization is not prepared for this change, it will lose many opportunities to be competitive.

Commentary by Dr. Valentin Fuster
2013;():V004T08A002. doi:10.1115/GT2013-94744.

The Department of Aeronautics at the United States Air Force Academy utilizes a closed-loop, two-dimensional turbine cascade wind tunnel to reinforce a learning-focused undergraduate thermo-propulsion sequence. While previous work presented in the literature outlined the Academy thermo-propulsion sequence and the contextual framework for instruction, this current paper addresses how the Academy turbine cascade facility is integrated into the aeronautical engineering course sequence. Cadets who concentrate in propulsion are to some extent prepared for each successive course through their contact with the cascade, and ultimately they graduate with an exposure to experimental research that enhances their grasp of gas turbine engine fundamentals. Initially, the cascade is used to reinforce airfoil theory to all cadets in the Fundamentals of Aeronautics course. Aeronautical engineering majors take this course during the first semester of their sophomore year. The next semester all aeronautical engineering majors take Introduction to Aero-thermodynamics. In this course, the closed-loop aspect of the cascade facility is used to reinforce concepts of work addition to the flow. Heat transfer is also discussed, using the heat exchanger that regulates test section temperature. Exposure to the cascade also prepares cadets for the ensuing Introduction to Propulsion and Aeronautics Laboratory courses, taken in the junior and senior year, respectively. In the propulsion course, cadets connect thermodynamic principles to component analysis. In the laboratory course, cadets work in pairs on propulsion projects sponsored by the Air Force Research Laboratory, including projects in the cascade wind tunnel. Individual cadets are selected from the cascade research teams for summer internships, working at an Air Force Research Laboratory turbine cascade tunnel. Ultimately, cadet experiences with the Academy turbine cascade help lay the foundation for a two-part senior propulsion capstone sequence in which cadets design a gas turbine engine starting with the overall cycle selection leading to component-level design. The turbine cascade also serves to integrate propulsion principles and fluid mechanics through a senior elective Computational Fluid Dynamics course. In this course, cadets may select a computational project related to the cascade. Cadets who complete the thermo-propulsion sequence graduate with a thorough understanding of turbine engine fundamentals from both conceptual and applied perspectives. Their exposure to the cascade facility is an important part of the process. An assessment of cadet learning is presented to validate the effectiveness of this integrated research-classroom approach.

Commentary by Dr. Valentin Fuster
2013;():V004T08A003. doi:10.1115/GT2013-95011.

This paper presents the perceptions of engineering students who followed podcasted courses during their higher education. Podcasting is widely used in remote education, but it also benefits on-campus students because it supports flexible and personalized teaching. The first three generations of students from an international Master’s degree program participated in a survey to give their impressions about the use of podcasting in their program. This preliminary survey targeted three aspects of podcasting: the format, the effect on learning experience, and the effect on student isolation. Results showed a majority of students considered recorded lectures a very helpful tool to support traditional on-campus lectures. The students appreciated the opportunity to pause and re-watch the videos to learn at their own pace. However, few students would consider a purely remote education; they felt less engaged in their education because of the lack of direct contact with teachers and peers. This highlights the importance of the social networking that happens on-site. In conclusion, the main advantage of podcasting is to compensate for the lack of individually adapted teaching in higher education. However, it will not completely replace traditional lectures without the development of both new tools to facilitate the professor-student interactions, and of teaching techniques to keep students engaged in their studies.

Commentary by Dr. Valentin Fuster
2013;():V004T08A004. doi:10.1115/GT2013-95139.

Recent experimental work characterized the performance of a unique cross-flow heat exchanger design for application of cooling compressor bleed air using liquid jet fuel before it is consumed in the gas turbine combustor. The proposed design has micro-channels for liquid fuel and cools air flowing in passages created using rows of intermittent fins. The design appears well suited for aircraft applications because it is compact and light-weight. A theoretical model is reported to be in good agreement with experimental measurements using air and water, thus providing a design tool to evaluate variations in the heat exchanger dimensions. This paper presents an evaluation of the heat exchanger performance with consideration of uncertainties in both model parameters and predicted results. The evaluation of the design is proposed to be reproduced by students in a thermal-fluids design class. The heat exchanger performance is reevaluated using the effectiveness–NTU approach and shown to be consistent with the method reported in the original papers. Results show that the effectiveness is low and in the range of 20 to 30% as well as the NTU which ranges from 0.25 to 0.50 when the heat capacity ratio is near unity. The thermal resistance is dominated by the hot gas convective resistance. The uncertainties attributed to fluid properties, physical dimensions, gas pressure, and cold fluid flow rate are less significant when compared to uncertainties associated with hot fluid flow rate, hot fluid inlet temperature, cold fluid inlet temperature, and convective correlation for gas over a finned surface. The model shows which heat transfer mechanisms are most important in the performance of the heat exchanger.

Commentary by Dr. Valentin Fuster
2013;():V004T08A005. doi:10.1115/GT2013-95217.

In the past several years, the traditional fourth year “hands-on” requirement for engineering programs in the US is being satisfied by what is now called Capstone Senior Design Project (herein referred to as CSDP). The engineering CSDP program director sends a call to the local industries within the State for solicitation of project proposals that will be worked on by the interdisciplinary engineering student team. Each industrial participant will have to contribute a preset budget defined by the program to the engineering school for each submitted proposal that has been selected by the student team. Honeywell has been an avid participant in the University of Arizona CSDP program for the past several years. Rather than define a simple CSDP that can be fully completed in the first attempt, the author has sought the value of teaching iterative design to the student team by defining a multi-year CSDP scope, in that after the first year, each successive team learns from the past design and implements its own improvement to the design it inherits. This paper gives an overview of Honeywell’s CSDP titled “Measuring Heat Transfer in Annular Flow Between Co-Rotating or Counter-Rotating Cylinders”. Now in its fourth iteration, each wave of student team has been able to understand the complexity of the design, the challenge of testing for structural integrity, the controllability of implementing a balanced system of heat gain and loss to reach steady state operation, the evolution of starting with slip ring temperature measurements and ending at wireless telemetry, DOE testing to rank influencing variables, and heat transfer correlation of the data relating Nusselt versus Reynolds number. Beginning with the first year CSDP team, this paper covers the design approach selected by that team, its results, and the lessons learned as a result of failure in meeting the full requirements, which is then taken on by the next group of students the following year.

Commentary by Dr. Valentin Fuster
2013;():V004T08A006. doi:10.1115/GT2013-95228.

Undergraduate courses at Technological Institute of Aeronautics (ITA) are 5-years course, divided into Fundamental (2 years) and Professional (3 years). The Flow Machines, in the Mechanical-Aeronautical Engineering Course, is offered by the Turbomachines Department and is taught in the first semester of the fourth year (2nd professional year). In the course, the basic theory, unified for all machines, is presented in details for the students, emphasizing the physics of all processes involved in the fluid-machine energy transfer. Incompressible and compressible fluids are treated accordingly. The flow machines types are individually studied, focusing attention to their performance characteristics and range of applications. The preliminary design and off-design operation issues are discussed in details with the students, with emphasis on relevant aspects of each machine, like cavitation, stall and surge. The students are taught on how to choose the flow properties at the blade edges for the sake of preliminary design and off-design performance estimations. Loss models are introduced during the theory classes and popular models are presented. At this point, in-house computer codes and commercial software are presented to the students, who are asked to solve simple problems. The installation, operation and basic performance calculations are also presented for the students during the lab classes for several hydraulic machines installed at ITA laboratories. All course material is transferred for the students in pdf format before classes. In this work, the experience with the teaching process in flow machines at ITA, theory and laboratory, is described.

Commentary by Dr. Valentin Fuster
2013;():V004T08A007. doi:10.1115/GT2013-95296.

The WebEngine is a web-based gas turbine performance simulation tool. The main advantage from this approach is the ease-of-use as no local installation is required. A number of different user categories such as students, researchers, gas turbine operators etc. can immensely benefit from this tool. The WebEngine has been under development for two years and is strongly supported by various associated research work in the department. It offers a large number of simulation capabilities such as design point and off-design single runs/parametric analysis, engine library, engine model design, virtual engine sensors and power plant operating plan. The WebEngine core is a high quality and robust gas turbine performance simulation code, developed by the Department of Power and Propulsion of Cranfield University, called Turbomatch. This approach offers modular component structure and high flexibility in the model development, as any engine configuration modelling is possible. In addition, the ergonomic graphical user interface offers a suitable and relaxing environment for the user. Related case studies are provided wherein a turbojet engine model development procedure, a turbofan design point fan pressure ratio optimization and an off-design parametric analysis are enumerated. Finally, a monthly power plant operating schedule is calculated for June 2013. A number of future additions is planned for the tool, with the diagnostics capability having the principal role.

Commentary by Dr. Valentin Fuster
2013;():V004T08A008. doi:10.1115/GT2013-95602.

An undergraduate student design and build project has been established by the US Air Force, Air Force Research Laboratory as part of an outreach program. During the 2011–2012 academic year, undergraduate students of six universities participated in designing a thrust vectoring system for a small (20 pound-thrust) jet engine. A description of the project parameters and student designs is given in this paper. It proved to be an extremely successful project, and other professors and students can learn from the different approaches taken by the six different teams and the project itself. Industry will also be interested in the depth and breadth of an undergraduate project that is being used to educate their future engineering workforce.

Topics: Thrust , Design
Commentary by Dr. Valentin Fuster
2013;():V004T08A009. doi:10.1115/GT2013-95631.

Undergraduate students of six universities participated in a design and build outreach program sponsored by the US Air Force during the 2011–2012 academic year. The goal was to design and build a thrust vectoring system for a small jet engine (about 20 pounds of thrust). Student and professor exit surveys were taken with almost all participants contributing to these surveys. Based on the survey results and the professors’ insights, learning outcomes and student impact are assessed. In addition, any other lessons learned during this extensive project-based learning activity are described.

Topics: Thrust , Design , Students
Commentary by Dr. Valentin Fuster
2013;():V004T08A010. doi:10.1115/GT2013-95749.

The preliminary design of turbomachinery components is strongly affected by the application process. This paper documents a compressor comparative design assessment which was conducted with the intent of to highlight the rationale of proposing a new propulsion system for use on short haul aircraft, similar to the Embraer E-Jet. This study establishes and discusses the compressor figures of merit pertaining to short haul operation and their influence on the desired compression layout.

A computational tool to undertake compressor designs is developed and validated against the NASA E3 published compressor layout. With the aid of this software, a few alternative compressor layouts that meet the established criteria are suggested.

The best candidates are highlighted and further studied in terms of individual design parameters such as temperature rise distribution, number of stages and off-design performance. The figures of merit that dictate particular design choices are highlighted and commented. The most advanced candidate design is found to yield a very respectable performance compared to current production engines of the same class. This work aims at highlighting the process through which a modern compression system is designed at a preliminary stage and the design challenges confronting it.

Commentary by Dr. Valentin Fuster
2013;():V004T08A011. doi:10.1115/GT2013-95778.

This paper describes the application of a weight and cost-estimating methodology used in an undergraduate aircraft engine design course that is taught in concert with a companion course in airframe design. The two preliminary designs, one for the engine and the other for the airframe, must be integrated as subsystems within a system to satisfy the performance requirements of a given mission as outlined in a single “request for proposals”. In recent years, systems engineering management majors have been added to the design teams to work alongside the aeronautical engineering majors to analyze and report on costs, schedule, and technical risk factors in addition to the operational performance factors that have previously been the sole focus of the course. The teaming of technical management majors and aeronautical engineering majors has been driven by a heightened emphasis on system affordability. The cost-estimating methodology for gas turbine engines uses cycle parameters such as turbine rotor inlet temperature, overall pressure ratio, specific fuel consumption, level of technology, and engine dry weight as inputs. A methodology for estimating dry engine weight was developed which uses engine cycle parameters and fan face diameter as inputs in a volume analog scaling factor which was correlated against historical engine weight data. To tie all of the performance, weight, cost, and development time issues together, the paper presents an “analysis of alternatives” example that considers three different engine cycle alternatives. The design tools presented in this paper will provide a strong foundational understanding of how to systematically weigh and evaluate the important tradeoffs between aircraft turbofan engine performance, cost, schedule, and risk factors. Equipping students with the insight and ability to perform these multidisciplinary trade studies during the preliminary engine design process is this paper’s most important contribution.

Commentary by Dr. Valentin Fuster

Electric Power

2013;():V004T09A001. doi:10.1115/GT2013-94056.

Economic reasons, leading to the use of coal and the environmental concerns, call for clean technologies for the electric power production. Accordingly the adoption of Integrated Gasification Combined Cycle (IGCC) plants with Carbon Capture and Storage (CCS) has been pushed. Such a technology is promising but it still shows some critical aspects. Some of them are related to stable and controllable operations of commercially available Gas Turbines (GTs) designed to be fed with Natural Gas (NG) once the original fuel is replaced by the hydrogen-rich syngas produced in an IGCC-CCS plant.

The thermo-physical properties of the H2-rich syngas require investigations and modifications of the combustor and of the turbomachines to meet stable and safe GT behaviour. Such properties strongly affect the matching between GT compressor and expander.

To run the GT with the syngas, various options can be taken into account. Some of them do not require GT flow function modifications, while other options involve compressor and expander structural changes.

In the present paper some compressor modifications that can be adopted to maintain an F Class GT performance and stability are explored. Such modifications have been analysed by means of a high fidelity quasi-one-dimensional model based on an Elemental Component Finite Volume approach for the GT sizing and analysis. Results have been compared and deeply discussed.

Commentary by Dr. Valentin Fuster
2013;():V004T09A002. doi:10.1115/GT2013-94466.

Power grids are continually subjected to variations in load demand, leading to imbalances between generation and consumption. Such imbalances have an impact on the frequency level, requiring ongoing frequency control. Timely response of sufficient magnitude is critical to ensure grid stability. Without appropriate controls, variation in frequency levels can compound, leading to trips or even blackouts.

Primary Frequency Control (PFC) and Regulation Margin Control (RMC) have recently become a requirement for gas turbine generators (GTG) by many transmission grid authorities. PFC provides grid stability by allowing the gas turbine to automatically increase (or decrease) load when a grid frequency deviation occurs outside of a frequency band, and maintains this increased (or decreased) load while the deviations persist. RMC is used to ensure that a percentage of the GTG generating capability is reserved for use when grid frequency excursions occur.

There are different grid control regulations for different countries and regions. For example, the European Grid Code requires enough Primary Reserve set aside to support a +/−200 mHz grid frequency deviation with associated response times. The GTG must keep a percentage of the unit’s power capacity, or Primary Reserve, available for this purpose. The size of Primary Reserve power contributed by the grid frequency deviation is determined by the RMC Margin and PFC Droop settings, and must be managed under a wide range of operating and ambient conditions.

This paper reviews field test results and lessons learned in developing an approach to meeting the grid requirements. This includes the PFC reserve power response to frequency deviations, associated tolerances, and additional controls required to optimize the spray-intercooling power augmentation system.

Commentary by Dr. Valentin Fuster
2013;():V004T09A003. doi:10.1115/GT2013-94467.

Combined heat and power (CHP) is an application that utilizes the exhaust heat generated from a gas turbine and converts it into a useful energy source for heating & cooling, or additional electric generation in combined cycle configurations. Compared to simple-cycle plants with no heat recovery, CHP plants emit fewer greenhouse gasses and other emissions, while generating significantly more useful energy per unit of fuel consumed. Clean plants are easier to permit, build and operate. Because of these advantages, projections show CHP capacity is expected to double and account for 24% of global electricity production by 2030. An aeroderivative power plant has distinct advantages to meet CHP needs. These include high thermal efficiency, low cost, easy installation, proven reliability, compact design for urban areas, simple operation and maintenance, fuel flexibility, and full power generation in a very short time period.

There has been extensive discussion and analyses on modifying purge requirements on cycling units for faster dispatch. The National Fire Protection Association (NFPA) has required an air purge of downstream systems prior to startup to preclude potentially flammable or explosive conditions. The auto ignition temperature of natural gas fuel is around 800°F. Experience has shown that if the exhaust duct contains sufficient concentrations of captured gas fuel, and is not purged, it can ignite immediately during light off causing extensive damage to downstream equipment.

The NFPA Boiler and Combustion Systems Hazards Code Committee have developed new procedures to safely provide for a fast-start capability. The change in the code was issued in the 2011 Edition of NFPA 85 and titled the Combustion Turbine Purge Credit. For a cycling plant and hot start conditions, implementation of purge credit can reduce normal start-to-load by 15–30 minutes. Part of the time saving is the reduction of the purge time itself, and the rest is faster ramp rates due to a higher initial temperature and pressure in the heat recovery steam generator (HRSG).

This paper details the technical analysis and implementation of the NFPA purge credit recommendations on GE Power and Water aeroderivative gas turbines. This includes the hardware changes, triple block and double vent valve system (or drain for liquid fuels), and software changes that include monitoring and alarms managed by the control system.

Commentary by Dr. Valentin Fuster
2013;():V004T09A004. doi:10.1115/GT2013-94584.

This paper describes a simplified physics-based method derived from fundamental relationships to accurately predict the dynamic response of the steam bottoming cycle of a combined cycle power plant to the changes in gas turbine exhaust temperature and flow rate. The method offers two advantages: (1) rapid calculation of various modes of combined cycle transient performance such as startup, shutdown and load ramps for conceptual design and optimization studies; (2) transparency of governing principles and solution methods for ease of use by a wider range of practitioners. Thus, the method facilitates better understanding and dissemination of said studies. All requisite formulas and methods described in the paper are readily amenable to implementation on a computational platform of the reader’s choice.

Commentary by Dr. Valentin Fuster
2013;():V004T09A005. doi:10.1115/GT2013-94680.

Being the European energy market in a sort of stagnation, flexibility is nowadays particularly profitable, with increasing care of environmental minimum load, maximum load and loading/unloading rate.

For its F class model AE94.3A4, Ansaldo Energia has identified two technical keys for success:

- Combustion stability

- Combustion efficiency

Thanks to a cooperation agreement with ENEL PRODUCTION, the largest Italian electricity utility, Ansaldo Energia had the possibility to design, introduce on one GT and test several combustion system modifications addressed to improve the performance of the whole GT by a synergy between proven design burners and cooling / sealing air optimization.

During 3 months, 5 combustion system configurations have been installed and tested on the GT made available from ENEL. Taking into account that each burner is equipped with different kinds of pilot injections, the number of effective tested configurations amounts to 11.

The configurations have been chosen in a large range of premixing ability, from high premixing to high diffusion rate. Due to the optimization of secondary air system, it has been necessary to install additional instrumentation in order to monitor the impact on the hot gas path components, with the aim of maintaining temperature conditions consistent with long life requirements.

In the end, 3 combustion configurations were identified as able to cover 3 ranges of environmental requirements as:

1 – High populated residential areas (NOx emission < 30 mg/Nm3)

2 – Medium populated or light industrial (NOx emission < 40 mg/Nm3)

3 – Very low populated areas or heavy industrial (NOx emission < 50 mg/Nm3)

Premixing is generally the more effective element to defeat N2 oxidation, with the side effect of making the combustion process particularly sensitive to pressure pulsations. So the efforts of the combustion designer have been spent to carefully modulate the injection of fuel in order to allow a good compromise between stability and emission.

Topics: Combustion , Testing
Commentary by Dr. Valentin Fuster
2013;():V004T09A006. doi:10.1115/GT2013-94902.

This paper summarizes the techniques and methods available today to allow for significant improvements of existing and previously upgraded Gas Turbine fleets, while keeping time to market and investment to the absolute minimum. This allows for flexibility to react to market changes and to extend the utilization of the customer’s assets. The successful application of these techniques is described using the example of the latest service upgrade of Alstom’s GT13E2 heavy duty gas turbine also showing first validation results.

In contrast to previous improvements, mostly focusing on an increase in power-output, this upgrade development followed a different strategy: As customers are demanding a reduction in Cost of Electricity, the focus this time was on increasing CC-efficiency and elongating service interval lengths. The design challenge has been to come up with an upgrade package, which limits the additional power-output while maximizing efficiency and lifetime at the same time. Limiting the additional power output is crucial to be retrofit-able into existing plants with a minimum in investment costs, as some plant components like Generators and Transformers, especially for previously upgraded units, may already be close to their capacity limits.

The paper describes in detail how the upgrade scope and design concept has been derived based on customer input. Among other measures, it is demonstrated how the consequent application of 3D design methods, the utilization of state-of the art airfoil profiling and clearance optimization in combination with an optimized thermodynamic cycle have been used to maximize the component and GT efficiencies. Furthermore it is shown how development time and risks have been minimized by a consequent application of a combined concurrent design & manufacturing approach and rapid prototyping methods for early design validation. Finally, short- and mid-term validation results after the first implementation and testing in spring 2012 are presented, confirming that the design targets have been met.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2013;():V004T09A007. doi:10.1115/GT2013-95024.

In typical heavy duty gas turbines the multistage axial compressor is provided with anti-surge pipelines equipped with on-off valves (blow-off lines), to avoid dangerous flow instabilities during start-ups and shut-downs. Blow-off lines show some very peculiar phenomena and somewhat challenging fluid dynamics, which require a deeper regard. In this paper the blow-off lines in axial gas turbines are analyzed by adopting an adiabatic quasi-unidimensional model of the gas flow through a pipe with a constant cross-sectional area and involving geometrical singularities (Fanno flow). The determination of the Fanno limit, on the basis of the flow equation and the second principle of thermodynamics, shows the existence of a critical pipe length which is a function of the pipe parameters and the initial conditions: for a length greater than this maximum one, the model requires a mass-flow reduction. In addition, in the presence of a regulating valve, so-called multi-choked flow can arise. The semi-analytical model has been implemented and the results have been compared with a three-dimensional CFD analysis and cross-checked with available field data, showing a good agreement. The Fanno model has been applied for the analysis of some of the actual machines in the Ansaldo Energia fleet under different working conditions. The Fanno tool will be part of the design procedure of new machines. In addition it will define related experimental activities.

Topics: Design , Gas turbines
Commentary by Dr. Valentin Fuster
2013;():V004T09A008. doi:10.1115/GT2013-95143.

This paper addresses recent industrial gas turbine compressor dependability issues and risk mitigation measures viewed from the end user’s perspective. Industrial reliability-availability-maintainability statistics related to power generation applications are reviewed. Several case histories with specific component issues involving blades and vanes are covered. Case histories are used to summarize field experience, engineering analysis and evaluation of related design and operating modifications as appropriate. Recent progress with setting up a field monitoring demonstration using pressure pulsations, vibration and acoustic emissions is summarized.

Commentary by Dr. Valentin Fuster
2013;():V004T09A009. doi:10.1115/GT2013-95497.

The operation of a gas turbine is the result of the aero-thermodynamic matching of several components which necessarily experience aging and degradation over time. An approach to treat degradation phenomena of the axial compressor is provided, with an insight into the impact they have on compressor operation and on overall GT performances. The analysis is focused on the surface fouling of compressor blades and on rotor tip clearances variation.

A modular model is used to simulate the gas turbine operation in design and off-design conditions and the aerodynamic impact of fouling and rotor tip clearances increase is assessed by means of dedicated loss and deviation correlations implemented in the 1D mid-streamline code of the compressor modules.

The two different degradation sources are individually considered and besides the overall GT performance parameters, the analysis includes an evaluation of the compressor degradation impact on the secondary air system.

Commentary by Dr. Valentin Fuster
2013;():V004T09A010. doi:10.1115/GT2013-95625.

In preparation for the next generation combined cycles, gas turbine technology development needs to continue to lower the lifecycle costs through increased efficiency, reduced first costs, extended maintenance cycles, and reduced emissions. It must also develop fast ramping capability, account for a wider variation in fuel composition and provide emission and performance effective part load operation. These needs will be met by refining state of the art technologies and adding new technologies. This paper will provide an overview of the recent research and development activities, the approach to bring them into a product and the resulting trend in Alstom gas turbine technologies.

Commentary by Dr. Valentin Fuster
2013;():V004T09A011. doi:10.1115/GT2013-96013.

Usually, the turbogenerators are designed to fire a specific fuel, depending on the project of these engines may be allowed the operation with other kinds of fuel compositions. However, it is necessary a careful evaluation of the operational behavior and performance of them due to conversion, for example, from natural gas to different low heating value fuels. Thus, this work describes strategies used to simulate the performance of a single shaft industrial gas turbine designed to operate with natural gas when firing low heating value fuel, such as biomass fuel from gasification process or blast furnace gas (BFG). Air bled from the compressor and variable compressor geometry have been used as key strategies by this paper. Off-design performance simulations at a variety of ambient temperature conditions are described. It was observed the necessity for recovering the surge margin; both techniques showed good solutions to achieve the same level of safe operation in relation to the original engine. Finally, a flammability limit analysis in terms of the equivalence ratio was done. This analysis has the objective of verifying if the combustor will operate using the low heating value fuel. For the most engine operation cases investigated, the values were inside from minimum and maximum equivalence ratio range.

Topics: Fuels , Gas turbines , Heating
Commentary by Dr. Valentin Fuster

Fans and Blowers

2013;():V004T10A001. doi:10.1115/GT2013-94100.

The aerodynamic and aeroacoustic performance of axial fans are strongly affected by the unavoidable tip clearance. Three identical fan impellers but with different tip clearance ratio were investigated. Details of the time averaged tip flow were analysed by a numerical RANS-simulation. Unsteady wall pressure fluctuations in the tip region of the rotating blades and on the interior wall of the duct type shroud and the overall sound radiated were measured. As the tip clearance is increased, overall fan pressure rise and efficiency drop, the onset of the rotating stall moves to higher flow rates and broadband noise is found to become dominant in the spectrum. The RANS simulation revealed a vortex system consisting of three different vortices in the tip region. Their strength and trajectories are controlled by the size of the tip clearance and the fan’s operating point. Measurements showed that these vortices impose tonal and — more pronounced — broadband pressure fluctuations on stationary and rotating walls in the vicinity of the blade tip. The tip vortex system is the main driver of the unsteady flow in the tip region. As tip clearance is increased the unsteady wall pressure becomes more developed and with it the sound radiated by the fan. Hence it is concluded that these vortex induced pressure fluctuations form the dipole source mechanism of the noise observed. This hypothesis is supported by a preliminary correlation analysis.

Commentary by Dr. Valentin Fuster
2013;():V004T10A002. doi:10.1115/GT2013-94157.

The aerodynamic and acoustic performance of a locomotive cooling module is optimized by a new design strategy for the fan unit. The fan selection or development of the cooling modules is usually based on the specific design point but without consideration of installation effects.

The new approach considers the fan development in a more integrated manner. A simplified 1:4 model of the cooling system is constructed and used for system analysis, numerical flow simulations, and experimental validation. The subsequent fan and guide vane optimization is based on numerical simulations embedded in an optimization algorithm taking installation effects into account. The noise emitted by the fan is addressed by a smoothed inflow velocity profile, a new blade sweep strategy, the reduction of secondary flows, and the reduction of fan size and rotational speed.

The optimized fan unit is then integrated into the non-simplified full-scale system. Experiments reveal an energy saving of 20% and an overall sound power level reduction of 6 dB with even higher reduction of the tone at blade passing frequency.

All results are discussed with respect to transferability to other cooling modules. It is found that a set of general design recommendations originates from this work, whereas the optimization loops would need to be repeated for other cooling module types.

Commentary by Dr. Valentin Fuster
2013;():V004T10A003. doi:10.1115/GT2013-94501.

The noise emitted by axial fans plays an integral role in product design. When conventional design procedures are applied, aeroacoustic properties are controlled via an extensive trial-and-error process. This involves building physical prototypes and performing acoustic measurements. In general, this procedure makes it difficult for a designer to gain an understanding of the functional relationship between noise and geometrical parameters of the fan. Hence, it is difficult for a human designer to control the aeroacoustic properties of the fan.

To reduce the complexity of this process, we propose an inverse design methodology driven by a genetic algorithm. It aims to find the fan geometry for a set of given objectives. These include, most notably, the sound pressure frequency spectrum, aerodynamic efficiency, pressure head and flow rate. Individual bands of the sound pressure frequency spectrum may be controlled implicitly as a function of certain geometric parameters of the fan.

In keeping with inverse design theory, we represent the design of axial fans as a multi-objective, multi-parameter optimization problem. The individual geometric components of the fan (e.g., rotor blades, winglets, guide vanes, shroud and diffusor) are represented by free-form surfaces. In particular, each blade of the fan is parameterized individually. Hence, the resulting fan is composed of geometrically different blades. This approach is useful when studying noise reduction.

For the analysis of the flow field and associated objectives, we utilize a standard RANS solver. However, for the evaluation of the generated noise, a meshless Lattice-Boltzmann solver is employed. The method is demonstrated for a small axial fan, for which tonal noise is reduced.

Commentary by Dr. Valentin Fuster
2013;():V004T10A004. doi:10.1115/GT2013-94548.

The idea of a railway tunnel under the Bosphorus Strait linking the European and Asian sides of Istanbul was first raised in 1860. Today the project is nearing completion with a design placing the tunnel on the seabed. In this paper the rationale for the tunnel is presented, and the practical problems associated with such a large civil engineering project in a busy urban area considered. Challenges associated with design of the tunnel ventilation system are reviewed, and the implications for tunnel ventilation fan design clarified. The design of three tunnel ventilation fan concepts is presented. First a two-stage counter rotating fan. Second a single-stage high speed fan. Third a two-stage fan with a single motor and impeller on each end of the motor shaft. The relative merits of each concept are considered in detail. The paper concludes with a description of the tunnel ventilation fan installation and maintenance philosophy. The practicality of installing and maintaining tunnel ventilation fans have a primary impact on the on-going ability of the tunnel ventilation fans to operate reliably and therefore on the tunnel’s availability. Lessons learnt and implications for on-going best practice are then summarised.

Commentary by Dr. Valentin Fuster
2013;():V004T10A005. doi:10.1115/GT2013-94588.

An important subsystem in most surface transport vehicles is the forced-air cooling module. Under specific operational conditions of the vehicle the cooling system is the major noise source and the component with the largest consumption of energy. A comprehensive time domain simulation model was developed for simulation of the cooling module in a Diesel locomotive under realistic operational conditions. It includes the components that produce waste heat such as the engine, the turbo transmission, the brake, etc. and the cooling module with its fans. Given the operation of the locomotive e.g. in terms of speed vs. time along a track and its load, data from experimental full scale tests agree well with predictions from the time domain model. The onset of cooling fan operation is predicted well, with it their instantaneous energy consumption and sound radiation. Three optimized cooling unit assemblies for the new locomotive Voith Gravita 15L had been developed and pre-assessed utilizing the model and eventually tested in the locomotive under realistic operational conditions. A new thermodynamically advanced cooling unit with aerodynamically and acoustically optimized fans was found superior by approx. 2 dB (A) less sound power radiation and some 30% less energy consumption as compared to the benchmark. It is anticipated that those advantages are even more distinct as the ambient temperature decreases.

The work is part of the European FP7 transport research project ECOQUEST.

Commentary by Dr. Valentin Fuster
2013;():V004T10A006. doi:10.1115/GT2013-94803.

This review aims to assist engineers understand and apply passive solutions for reducing industrial fan noise. The paper systematically reviews the extant literature on passive noise techniques, with a particular focus on experimental rather than theoretical research. The review provides an assessment of the current state of the art in industrial fan flow and noise control. It offers a vision for potential improvements in noise reduction via novel application of flow and noise control technologies.

The review examines the interaction between aerodynamic cause and acoustic effect and the application of control technologies that current cause and effect theories have inspired. The purpose is to provide a vision for aerodynamics research during the next decade that will serve as a basis for systematically reducing industrial fan noise emissions. The review provides an assessment of recent flow and noise control advances, and considers some opportunities for future research.

The review reflects an emphasis on low speed industrial fans. The authors consider high-speed turbomachinery noise control, with the objective of illustrating the linkages between the two technologies. The review concludes with a summary of the opportunities for future research and its application to flow and noise control in industrial fan design.

Topics: Noise control , Fans
Commentary by Dr. Valentin Fuster
2013;():V004T10A007. doi:10.1115/GT2013-94853.

We report on a numerical study on the performance of an innovative axial flow fan for large tunnel ventilation. Taking a lead from a previous biomimetic analysis on the performance of the flippers of the humpback whale, this whale-fan was designed with sinusoidal-like leading edge that mimic the tubercles of the whale. We found that this provided a resistance to stall and improved lift recovery in post-stall operations. The sinusoidal profile of the leading edge allowed to control the distribution of vorticity on the suction surface of the blades and increase the stall margin of the device.

The paper discusses the design methodology that was followed to correlate the sinusoidal shape of the leading edge of the blade with the desired vorticity distribution at the trailing edge that was needed to control separation.

In the paper we show the results of numerical computations carried out with the finite volume open-source code OpenFOAM on the whale-fan as well as a baseline fan with straight leading edge. Reynolds Averaged Navier-Stokes equations for incompressible flow were solved with a non-linear (cubic) eddy-viscosity k-ε model that was found able to control the eddy viscosity distribution in order to account for anisotropy of Reynolds stresses and better reproduce the three-dimensional properties of the flow field.

The paper shows the performance chart of the whale-fan, derived from numerical computations, and gives an insight of the fluid flow mechanisms that are generated by the sinusoidal leading edge on the suction surface of the fan. A comparison with the baseline fan with straight leading edge is provided in order to highlight how the shape of the leading edges affect the performance of the fan.

Topics: Ventilation , Fans
Commentary by Dr. Valentin Fuster
2013;():V004T10A008. doi:10.1115/GT2013-94932.

A generalized model for mapping the trend of the performance characteristics of a double-discharge centrifugal fan is developed based on the work by Casey and Robinson (C&R) which formulated compressor performance maps for tip-speed Mach numbers ranging from 0.4 to 2 using test data obtained from turbochargers with vaneless diffusers. The current paper focuses on low-speed applications for Mach number below 0.4. The C&R model uses four non-dimensional parameters at the design condition including the flow coefficient, the work input coefficient, the tip-speed Mach number and the polytropic efficiency, in developing a prediction model that requires limited geometrical knowledge of the centrifugal turbomachine. For the low-speed fan case, the C&R formulas are further modified to apply a low-speed, incompressible analysis.

The effort described in this paper begins by comparing generalized results using efficiency data obtained from a series of fan measurements to that using the C&R model. For the efficiency map, the C&R model is found to heavily depend on the ratio of the flow coefficient at peak efficiency to that at the choke flow condition. Since choke flow is generally not applicable in the low-speed centrifugal fan operational environment, an alternate, but accurate estimation method based on fan free delivery derived from the fan test data is presented. Using this new estimation procedure, the modified C&R model predicts reasonably well using the double-discharge centrifugal fan data for high flow coefficients, but fails to correlate with the data for low flow coefficients. To address this undesirable characteristic, additional modifications to the C&R model are also presented for the fan application at low flow conditions.

A Reynolds number correction is implemented in the work input prediction of the C&R model to account for low-speed test conditions. The new model provides reasonable prediction with the current fan data in both work input and pressure rise coefficients. Along with the developments for the efficiency and work input coefficient maps, the use of fan shut-off and free delivery conditions are also discussed for low-speed applications.

Topics: Design , Fans
Commentary by Dr. Valentin Fuster
2013;():V004T10A009. doi:10.1115/GT2013-94982.

Large centrifugal fans in cement factories operate in an aggressive environment, as the cement particles dispersed in the flow are responsible for strong blade surface erosion that leads to performance degradation.

This paper reports on the simulation of the flow field in a large centrifugal fan designed for process industry applications. The aerodynamic investigation, at a preliminary level, highlights the critical regions inside the device and suggests possible modification to increase its duty life.

This paper reports on the simulation of the flow field in a large centrifugal fan designed for process industry applications. The aerodynamic investigation, at a preliminary level, serves the aim of highlighting the critical regions inside the device and suggest possible modification to increase its duty life.

In the paper we show the results of numerical computations carried out with the finite volume open-source code OpenFOAM using Multiple Reference Frame methodology. Reynolds Averaged Navier-Stokes equations for incompressible flow were solved with standard eddy-viscosity k-ε model in order to explore the aerodynamic behaviour of the fan in near-design operations. The incompressible flow hypothesis was adopted even if locally Mach number can exceed 0.5. In fact in this case the pressure-rise does not lead to a variation of the density able to affect the velocity field divergence.

Given the high performance of the investigated impeller, the present work has a twofold objective. First, we seek to define an accurate numerical methodology to investigate high-pressure radial fans. Second, we provide detailed analysis of the inlet ring-impeller-volute assembly inner workings under realistic distorted inflow conditions.

The results provide the evolution of the pressure field in order to validate the accuracy of the simulation in reproducing the motion inside the fan that was fundamental for credible particle dispersion reproduction. We then investigate the three-dimensional flow field through the impeller in order to provide details about the secondary flow structures that develop within the blade vanes.

Commentary by Dr. Valentin Fuster
2013;():V004T10A010. doi:10.1115/GT2013-95269.

Investigation of the nature and properties of dynamic processes using different methods of processing of the measured signals may lead to erroneous interpretations and conclusions. One of the reasons for erroneous interpretations is applying only one analysis method. The use of two different methods allows reducing erroneous conclusions but does not eliminate them completely. Such erroneous conclusions concerning pressure oscillations during rotating stall in axial compressors are described when two conventional methods of information processing (auto-correlation functions and frequency characteristics) were used for analyzing processes with changing frequencies and amplitudes of oscillation. These methods have been used for the analysis of aerodynamic processes during little change in frequency (a process very close to the established). This led to an erroneous estimation of the characteristics of the investigated process, namely to the interpretation of a beating effect during established rotating stall. It is shown that the use of a third method — the method of spectrograms — may allow the correct interpretation of the process, showing the absence of beats and the existence of a small change of main frequency of the rotating stall during the process, interpreted as established process. At the same time, it is shown that in the initial transient stage of pressure oscillation prior to the establishment of the rotating stall, beating or processes close to it can be observed.

Topics: Pressure , Signals
Commentary by Dr. Valentin Fuster

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