ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V002T00A001. doi:10.1115/GTINDIA2017-NS2.

This online compilation of papers from the ASME 2017 Gas Turbine India Conference (GTINDIA2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Structures and Dynamics

2017;():V002T05A001. doi:10.1115/GTINDIA2017-4534.

This paper describes finite element (FE) analysis of a rotor-bearing system having a functionally graded (FG) shaft with a transverse breathing crack. Two nodded Timoshenko beam element with four degrees of freedom (DOFs) per node has been considered and effects of translational and rotary inertia, transverse shear deformations, and gyroscopic moments are also considered. The FG shaft is considered to be composed of zirconia (ZrO2) and stainless steel (SS) with the volume fraction of SS increasing towards the inner radius of the shaft. Thermo-elastic material properties are considered in the radial direction of the FG shaft following power law gradation. Local flexibility coefficients (LFCs) of the cracked FG shaft are determined analytically as a function of crack size, power law gradient index (k), and temperature with crack orientation using the Castigliano’s theorem and Paris’s equations which are used to compute the stiffness matrix in the FE analysis. The FE formulation has been validated with the analytical and FE solutions reported in the literatures, and then natural frequencies and whirling (forward and backward) frequencies are determined. Influences of crack size, power law gradient index, slenderness ratio, and temperature gradient with crack orientation, on the dynamic responses of the rotor-bearing system with an FG shaft are studied. Results show that the power law gradient index has significant influence on the natural frequencies and whirling frequencies for the rotor-bearing system with the breathing cracked FG shaft and the choice of power law index could play an important role in design of FG shafts under thermo-mechanical environment from the view point of damage tolerant design.

Commentary by Dr. Valentin Fuster
2017;():V002T05A002. doi:10.1115/GTINDIA2017-4535.

This paper studies the rotor dynamic behavior of misaligned-coupled rotor systems integrated with active magnetic bearings. The simplest possible numerical model has been derived with a 4-degree of freedom two coupled Jeffcott rotor systems. The effect of flexible coupling on the interaction between the response due to unbalance and misalignment has been studied. To demonstrate the influence three cases have been considered a) pure misalignment b) pure unbalance c) presence of both unbalance and misalignment. This is an original attempt considering the standard practice of using beam element based finite element modeling techniques for such systems. To simplify the problem, the weight dominance of discs has been assumed. Also the coupling considered in the problem is of flexible type. Misalignment in coupled rotors has been reported in literature to produce all harmonics both odd and even (...−2, −1, 0, 1, 2...) on either side of full spectrum. A suitable coupling excitation function has been chosen so that the response yields all the harmonics in spectrum. The numerical simulation has been performed in MATLAB/SIMULINK™ to generate the responses in time domain. Though AMB is incorporated in the system for vibration attenuation, the emphasis of the present paper shall be to demonstrate the interplay between unbalance and misalignment in flexibly coupled rotor systems.

Topics: Rotors
Commentary by Dr. Valentin Fuster
2017;():V002T05A003. doi:10.1115/GTINDIA2017-4537.

In the present article, the responses of a double cracked simply supported beam have been investigated. The responses of the structure are determined using Duhamel integral method numerically and validated with finite element analysis (FEA) using ANSYS WORKBENCH 2015 along with experimental verifications. The mass is moving on the structure in terms of critical speed of the structure. The normalized deflections of the structure at different damaged configurations are calculated. The influences of speed, mass, crack depth and crack location on the structures response are investigated. It is observed that the results obtained from Duhamel integral converge well with FEA and experimental verifications.

Commentary by Dr. Valentin Fuster
2017;():V002T05A004. doi:10.1115/GTINDIA2017-4569.

Vibration related issues such as flutter have always been a cause of concern for aircraft engine designers. They not only incur unwarranted cost and time overruns, but also significantly compromise performance and can cause structural damage. This phenomenon has become more relevant for the modern aircraft engines, which employ relatively thin, long blade rows to satisfy ever growing demand for a powerful yet compact engine. The tip sections of such blade rows operate with supersonic relative velocity, where prediction of flutter can get challenging due to unsteady flow features like oscillating shocks and their interaction with the blade motion. Linear cascades that represent a specific radial location of the rotor have proven to be a reliable tool for flutter studies. To facilitate flutter experiments at flow Mach numbers realistic to the aircraft engine components, a transonic cascade facility operating at a Mach Number (M) of 1.3 with the ability to oscillate the central blade in the cascade has been developed. The cascade consists of 5 blades and two false blades of which the central blade is oscillated in heave, which represents the bending mode of the rotor. The typical reduced frequencies associated with this kind of flutter in practice (k ∼ 0.1) correspond to a high dimensional frequency of 200 Hz for the present case. A barrel cam mechanism is used to provide such high frequency oscillations. The parameters varied in the present study include the reduced frequency (k) and the static pressure ratio (SPR) across the cascade, which is varied with the help of tailboard and flap arrangement located at the back end of the cascade. Three SPR cases of 1.05, 1.25, and 1.35 are considered and at each of these pressure ratio cases, the reduced frequency is varied. The unsteady loads are measured on the oscillating central blade during the oscillation cycle to quantify the energy transfer from flow to blade and shadowgraphy is used to visualize the shocks. The results from these experiments indicate flutter at lower k values for all the SPR cases tested, while the higher k values are damped. The magnitude of excitation or damping at any particular frequency is also observed to increase with increasing SPR.

Commentary by Dr. Valentin Fuster
2017;():V002T05A005. doi:10.1115/GTINDIA2017-4599.

The structural integrity and reliability of impeller–shaft assembly in a centrifugal air compressor or any turbo machinery is of at most importance for the trouble free operation. It is thus necessary to avoid any excitation that can cause a resonance for the impeller–shaft system. Considering above, a study on the resonance due to excitation from impeller–stator interaction is undertaken.

This paper deals with the construction of impeller interference diagram from the nodal diameters predicted from the cyclic symmetric model of a prototype impeller using ABAQUS. The excitations frequencies arising from impeller–diffuser and impeller–scroll tongue interactions are identified and calculated for the given impeller, diffuser and scroll system. These excitation frequencies are validated for a similar impeller through noise testing and concluded as potential excitation to be considered in design. Stress analysis was carried out to study stresses caused due to centrifugal forces & aerodynamic forces. A nonlinear Static analysis was carried out to account for dynamic stiffening due to centrifugal forces, prior to natural frequency extraction. The Campbell and SAFE diagrams are constructed and the interfering frequencies are identified from the plots constructed in a spread sheet. The nodal diameter versus harmonic force matrix is constructed to understand the forces that can excite a particular nodal diameter for both impeller and impeller–diffuser. From this analysis, it was inferred that diffuser pass frequency was exciting the impeller nodal diameter. Further, analysis was performed to evaluate dynamic stress by carrying out harmonic analysis.

Study was carried out to shift natural frequencies of impeller without significantly affecting aerodynamic performance. Iteratively disk back face design, disk thickness, blade thickness & blade geometry were modified to shift frequencies. Frequency extraction procedure was automated by developing user defined macro in ABAQUS.

After carrying out study and evaluating possible design Iterations, modifying the impeller blade geometry or altering frequency of source excitation by decreasing the number of diffuser blades were two possible solutions. The effect of both is studied in this paper.

Commentary by Dr. Valentin Fuster
2017;():V002T05A006. doi:10.1115/GTINDIA2017-4607.

Generally, Gas Foil Bearings (GFBs) are used in high speed machineries which are quite prone to instability or wear and tear. The current trend is to develop hybrid bearings which has conventional bearing (GFB) along with active magnetic bearing as an electromagnetic actuator (EMA). The GFBs are used for normal operation and the magnetic actuator can be used for the improvement of the stability and the load capacity of the bearing. In the present work a numerical study has been carried out to study the effects of magnetic actuator on the stability of bump type GFB supported rigid rotor. A rigid rotor supported on two identical GFBs with and without EMA has been investigated. The electromagnetic forces are incorporated in the equation of motion to provide the active control. A PD controller has been used as a controller for the magnetic actuator. It has been observed that the incorporation of EMA to the GFB reduces the sub synchronous vibrations and hence increases the stability.

Commentary by Dr. Valentin Fuster
2017;():V002T05A007. doi:10.1115/GTINDIA2017-4615.

Centrifugal pumps (CPs) are crucial components in many plant operations. However, they are susceptible to failures due to mechanical faults and/or fluid flow abnormalities. These faults not only affect the CP system but also affect the systems delivering flow to it or receiving flow from it. Therefore, it is extremely crucial to recognize the faults and estimate their severity during operation, so that a corrective action may be initiated. In the present work, an attempt has been made to develop a flexible algorithm based on support vector machine (SVM) suitable to classify CP faults, like the suction and discharge blockages (with varying severities), impeller defects, pitted cover plate faults and dry runs. Also, a combination of mechanical faults (impeller defects and pitted cover plate faults) and suction and discharge blockage faults are considered. For the sake of classification, the CP vibration data and the motor line-current data are generated in time-domain for each fault experimentally. Furthermore, industrially operating CP signatures cannot be immune to noise generated from other operating equipment in the premises. Hence, to assess the robustness of the developed methodology, signals are corrupted by adding 5%, 10% and 25% additive white Gaussian noise. The developed algorithm is tested with corrupted data. The efficiency of fault predictions obtained while testing with noisy and non-noisy data are compared. The results are very promising and carry a high potential for industrial applications.

Commentary by Dr. Valentin Fuster
2017;():V002T05A008. doi:10.1115/GTINDIA2017-4616.

The presence of crack introduces local flexibilities and changes physical characteristics of a structure which in turn alter its dynamic behavior. Crack depth, location, orientation and number of cracks are the main parameters that greatly influence the dynamics. Therefore, it is necessary to understand dynamics of cracked structures. Predominantly, every material may be treated as viscoelastic and most of the time material damping facilitates to suppress vibration. Thus present study concentrates on exploring the dynamic behavior of damped cantilever beam with single open crack. Operator based constitutive relationship is used to develop the general time domain, linear viscoelastic model. Higher order equation of motion is obtained based on Euler-Bernoulli and Timoshenko beam theory. Finite element method is utilized to discretize the continuum. Higher order equation is further converted to state space form for Eigen analysis. From the numerical results, it is observed that the appearance of crack decreases the natural frequency of vibration when compared to an uncracked viscoelastic beam. Under cracked conditions, the viscoelastic Timoshenko beam tends to give lower frequency values when compared to viscoelastic Euler-Bernoulli beam due to shear effect.

Commentary by Dr. Valentin Fuster
2017;():V002T05A009. doi:10.1115/GTINDIA2017-4621.

The analytical modelling and real time estimation of electromagnetic forces brings many challenges and in many situations, it is very difficult to develop an accurate model of force production. The present work describes an estimation of the actual forces generated by an electromagnetic actuator based on augmented Kalman filter.

A cantilever beam with end concentrated mass has been chosen as a vibrating system and an E–shaped laminated core with coils on the middle limb has been chosen as the electromagnetic exciter. The available analytical formulation has been chosen for the calculation of the generated forces which have been corrected using augmented Kalman filter.

The developed experimental setup has a mild steel beam of 150 mm length with a mass of 560 g at its tip and an E shaped lamination core with a stack thickness of 38 mm.

Topics: Kalman filters
Commentary by Dr. Valentin Fuster
2017;():V002T05A010. doi:10.1115/GTINDIA2017-4641.

In this article, a rotor–bearing–coupling system supported by Active Magnetic Bearings (AMBs) is numerically simulated to estimate the characteristic parameters of AMB, residual unbalance, and misalignment parameters. The system is modeled with two rigid massless rotors each having a rigid disc and an AMB at its mid-span, mounted on flexible bearings and connected together with a flexible coupling. Proportional–Differential–Integrator (PID) is used to control the controlling current in AMB. Lagrange’s equation is used to obtain the linear equations of motion (EOMs) of the system. The developed EOM is solved by the fourth order Runga–Kutta method to generate the displacement and current responses. The time domain responses are converted into frequency domain by using Fast Fourier Transform (FFT) and full spectrum analysis is carried out to estimate the characteristic parameters of rotor AMB system. The estimation of parameters is performed based on least squares approach in frequency domain. The proposed methodology is tested against different levels of measurement error and modelling error to check the robustness of the algorithm.

Commentary by Dr. Valentin Fuster
2017;():V002T05A011. doi:10.1115/GTINDIA2017-4646.

Steady-state and dynamic characteristics of two-lobe journal bearing, operating on TiO2 based Nano-lubricant has been obtained. The effective viscosity is obtained by using Krieger-Dougherty viscosity model for a given volume fraction of nanoparticle in the base fluid. Various bearing performance characteristics are then obtained by solving modified Reynolds equation for variable viscosity model and couple stress model. The stiffness and damping coefficients are also determined for various values of the volume fraction of the nanoparticle in the nanofluid. Results reveal that load carrying capacity and flow coefficient increase whereas friction variable decreases without affecting the stability condition of two-lobe journal bearing operating on TiO2 based nanolubricant. On the other hand attitude angle and dynamic coefficients remains constant for all the values of volume fraction of nanoparticle.

Commentary by Dr. Valentin Fuster
2017;():V002T05A012. doi:10.1115/GTINDIA2017-4662.

High asynchronous self-excited blade response was observed in a transonic first stage rotor during the evaluation of flutter stability in high forward speed conditions. This candidate baseline rotor stage is a highly loaded, snubber-less bladed-disc configuration mounted in an axial low pressure compressor with tip speed in the order of 400 m/s. During the tests, the high asynchronous blade response was measured by strain gages, tip timing system and unsteady blade pressure transducers, which were correlated with analytical predictions. To alleviate this problem, it was attempted to tailor the first rotor blade configuration alone by adhering to all the constraints such as geometric, aerodynamic matching, material selection and utilising the same dovetail root configuration in the existing disc configuration. While tailoring the rotor blade, the critical blade parameters such as axial chord, thickness to chord, stagger, camber, leading and trailing edge radius were iterated from hub to tip. In the tailored rotor blade, the first flexure mode frequency, 1F was improved by 45% whereas the separation between second flexure, 2F and torsion mode, 1T were improved by over 30% with 4.9% weight penalty. Using the one way fluid-structure interaction approach, the blade incidence variation for different inlet pressure conditions and aerodynamic damping were evaluated using energy method for both the configuration. Blade sets of the tailored configuration were manufactured and tested in a dedicated compressor test facility, where characteristics were generated from 70% to 100% corrected speeds. The rig tests confirmed the predicted compressor performance as well as the improvement of natural frequency using blade mounted strain gages for the tailored blade. Upon the verification in the test rig, the tailored rotor configuration was further fitted in the engine and tested up to 103.3% of its design speed. The blade experienced two different inlet total pressure conditions in the test rig and engine tests. The unsteady pressure transducers and blade tip timing sensors did not show any asynchronous response in the corrected speed range for the tailored configuration. Compared to the baseline rotor blade, this tailored rotor blade demonstrated the absence of asynchronous response in the fundamental flexure mode and also well correlated with the aerodynamic damping prediction by energy method. Using this correlation, it is further analytically demonstrated that the blade will have sufficient aerodynamic damping at higher forward speeds and also minimal incidence variation in these conditions.

Commentary by Dr. Valentin Fuster
2017;():V002T05A013. doi:10.1115/GTINDIA2017-4681.

A comprehensive multi-objective optimisation methodology is presented and applied to a practical aero engine rotor system. A variant of Nondominated Sorting Genetic Algorithm (NSGA) is employed to simultaneously minimise the weight and unbalance response of the rotor system with restriction imposed on critical speed. Rayleigh beam is used in Finite Element Method (FEM) implemented in-house developed MATLAB code for analysis. The results of practical interest are achieved through bearing-pedestal model and eigenvalue based Rayleigh damping model. Pareto optimal solutions generated and best solution selected with the help of response surface approximation of the Pareto optimal front. The outcome of the paper is a minimum weight and minimum unbalance response rotor system which satisfied the critical speed constraints.

Commentary by Dr. Valentin Fuster
2017;():V002T05A014. doi:10.1115/GTINDIA2017-4684.

Slight variances in the manufacturing of rotating machinery can lead to significant changes in the structural dynamic behavior compared to the behavior of ideal cyclic periodic structures. Therefore it is necessary to consider deviations from the perfect cyclic periodic structures in the mechanical design process of rotating machinery. To minimize the effort of numerical calculations, the application of reduced order models is indispensable.

The objective of this paper is the comparison of two reduction methods which are not widespread in application of rotationally periodic structures. For the validation of the implemented methods, a generic model of a thin plate meshed with shell elements and a representative large size FE model of a radial turbine wheel are used. The first reduction method is called Improved Reduced System and is based on the classical Guyan reduction. The second reduction method is called SEREP method and is from a theoretical point of view closely related to the first method although the procedure to obtain the reduction basis is quite different. The results show for both test cases an excellent agreement between the reduced order models and the unreduced finite element model. Both reduction methods are also able to capture the phenomena of mode localization. It is also found that through the application of the reduced order methods the computation time can be reduced by two orders of magnitude. Based on the first reduction method, the statistical mistuning behavior is studied using the accelerated Monte Carlo simulation.

Commentary by Dr. Valentin Fuster
2017;():V002T05A015. doi:10.1115/GTINDIA2017-4696.

Squeeze film dampers have traditionally been used in aircraft engine to overcome stability and vibration problems that are not adequately handled with conventional style bearings. One of the key design features in a squeeze film damper [1] configuration is the introduction of flexibility in the bearing support. The simplest means to provide the support flexibility in the squeeze film damper is through the use of squirrel cage [2]. This paper deals with structural design analysis of cylindrical squirrel cage of an aircraft engine. Design of the squirrel cage needs a balance between stiffness and strength requirements. To meet the strength, stiffness and fatigue life requirements, squirrel cage web dimensions and fillet radius are modified. The various configurations of the squirrel cage have been evaluated to arrive at the optimum design. Stress analysis of the bearing has been carried out for axial, radial unbalance loads. Stress distribution in the web region has been studied in detail. High cycle fatigue life margins are estimated using Goodman diagram. The squirrel cage web dimensions and fillet radius are modified to improve HCF life requirements. The operating stresses in the squirrel cage are reduced while meeting the stiffness and HCF life requirements of the component.

Commentary by Dr. Valentin Fuster
2017;():V002T05A016. doi:10.1115/GTINDIA2017-4703.

Fasteners are typically designed to withstand axial or shear loads in a joint assembly. However, in selected scenarios fasteners are subjected to combination of axial, shear and bending loads. The criterion typically used to predict the ultimate failure of a member in combined shear and tension is based on the maximum normal stress and maximum shear stress theories. Test conducted by NASA found that under joint separation condition, the existing combined loading failure criteria over-predicts the strength of the bolts.

This paper develops the methodology of predicting fastener failure using finite element analysis with elasto-plastic material properties under combination of axial load and shear using a strain-based failure criterion. This methodology is validated with NASA test results. Elasto-plastic finite element analysis is shown to be an effective way to simulate test results. In order to define the full range capability values for different combinations of shear and tension loads, several cases were run with different load values. The study further extends to identify new limiting criteria under a combination of axial load and offset shear conditions for a selected stud.

The load capability can be used to calculate margin of safety for flange-joints. Further this approach can be generalized for application to all pins and fasteners subjected to combined shear and tension loads.

Commentary by Dr. Valentin Fuster
2017;():V002T05A017. doi:10.1115/GTINDIA2017-4709.

The vortex-induced vibration (VIV) of a rotating blade is studied in this paper. Euler-Bernoulli beam equation and the nonlinear oscillator satisfying Van der Pol equation are used to model the rotating blade and vortex shedding, respectively. While the fluctuating lift due to vortex shedding acts on the blade and the blade is coupled with fluid through a linear inertial coupling, resulting in a fluid-structure interaction problem. The coupled equations are discretized by using modes which satisfy the Eigenvalue problem. The work attempts to understand the instabilities associated with the frequency lock-in phenomenon. The method of multiscale is used to obtain the frequency response equation and frequency bifurcation diagrams of the coupled system. They are obtained for the primary (1:1) resonance for different values of the coupling parameter. The stability of the solution is presented by examining the nature of the Eigenvalues of the Jacobian matrix.

Commentary by Dr. Valentin Fuster
2017;():V002T05A018. doi:10.1115/GTINDIA2017-4715.

The vibrations involved in a typical axial compressor rotor in an aircraft engine are complex. Generally, the compressor blades are arranged in a cantilever type configuration. It is also known that the amplitude of vibration is highest near the tip section of the shroudless blade. Compressors are limited by aerodynamic instabilities such as rotating stall and surge. Rotating stall generally initiates near the tip region of the compressor. Blade vibrations coupled with aerodynamic instabilities will lead to a catastrophic scenario of flutter that is asynchronous to the rotor speed. This aeroelastic interaction is detrimental if not taken into consideration. Knowledge of vibration characteristics of the compressor rotor will help in mapping the flutter zone for safe operation.

The modal characteristics of the transonic axial compressor rotor available at the Axial Flow Compressor Research (AFCR) facility of National Aerospace Laboratories (NAL) are established in this study. A cyclic-symmetric pre-stressed modal analysis is performed on a single sector of the compressor rotor consisting of a shroudless blade connected to the disk with a pin type dovetail arrangement for different speeds. The main diagnostic charts for turbomachinery vibration i.e., Campbell and Interference diagrams are generated for various speeds and harmonic indices/ nodal diameters of the compressor rotor. The critical crossings of the engine order excitation lines over the natural frequencies of the blade are highlighted.

Experimental modal investigations and analysis are carried out on the compressor rotor at the stationary condition and for two different boundary conditions. First, the blade alone modal characteristics under the free-free condition are established. Later, the complete blade-disk assembly mounted on a base test-stand is used to investigate the cantilever fixed-free boundary condition of the chosen blade.

The modal characteristics are established by performing impact hammer experiments. Blade excitation is provided by a calibrated Dytran make impact hammer and the response is measured using a calibrated accelerometer.

The structural dynamic data acquisition hardware and software from OROS is used for determining the natural frequencies, mode shapes and structural damping for each mode of the compressor rotor. There is a good agreement in the natural frequencies and mode shapes established using experiment and numerical methods for the first three modes investigated. Modal Assurance Criteria (MAC) analysis is carried out for two different modal identification algorithms to compare the mode shapes.

Commentary by Dr. Valentin Fuster
2017;():V002T05A019. doi:10.1115/GTINDIA2017-4722.

In this paper, the natural frequencies of pre-twisted cantilever blades of various angles of twist having different airfoil cross sections in the NACA 6 series have been determined. The main objectives of this paper are to replicate the results previously published for the similar types of blades but with the assumption of a uniform rectangular cross-section and to compare it with the results obtained for blades with more refined airfoil cross-sections. Cantilevered type clamped-free boundary conditions have been used in this paper for all blades.

The comparison of the natural frequencies among different airfoils of the same NACA series has also been described in the paper in order to find out if any parameter of the airfoil such as camber, maximum thickness etc have any significant role in changing the frequencies of the beam. Commonly used commercial codes for finite element analysis have been used to determine these results.

Topics: Blades , Airfoils
Commentary by Dr. Valentin Fuster
2017;():V002T05A020. doi:10.1115/GTINDIA2017-4727.

The fatigue life of the titanium alloy axial compressor rotor blade was estimated based on stress based life method. The fatigue life of the compressor blade was evaluated through incremental amplitude test method. The incremental amplitude test method involves cumulative fatigue damage at different stress levels by using Miner’s Hypothesis. The probabilistic analysis of fatigue life was carried out by Weibull distribution method. The analytical and test methods results were compared and found satisfactory.

Commentary by Dr. Valentin Fuster
2017;():V002T05A021. doi:10.1115/GTINDIA2017-4733.

Rotating as well as static components of aero engines such as rotors and casings must be capable of withstanding vibrations which arises from various engine order excitations. HCF is attributed as one of the major failures due to its high crack propagation rate. The tolerances to vibration have become a key point to avoid resonance in operating range. Analytical predictions of individual components gives better accuracy and good agreement with test data. However, when the components are assembled, the accuracy of analyses can considerably depreciate since models describing stiffness and friction properties of joints are linearized. In such conditions proper predictions of dynamic response becomes difficult and may lead to under prediction or over prediction of dynamic response.

A nonlinear analysis is required to study the influence of joints flexibility on dynamic response. In this paper different nonlinear joint models are investigated to assess the dynamic behavior of the contact interface in terms of slipping and sticking contact parameters. The study shows significant changes over dynamic characteristics when compared to linear analysis. From this study, it is evident that nonlinear behavior of the contact in dynamic analysis phase due to slip and separation plays vital role over the dynamic characteristics of the component. This study emphasizes to consider physical behavior of joints in dynamic analysis to avoid catastrophic HCF failures.

Commentary by Dr. Valentin Fuster
2017;():V002T05A022. doi:10.1115/GTINDIA2017-4734.

Present work focuses on the dynamic modelling of the dual-disc rotor supported on oil-free bearings idealizing a turbocharger rotor bearing system. The equations of motion of the rotor system are formulated and solved by finite element method to obtain the dynamic response of the system. The gas-foil bearing forces obtained from finite-difference approach at each time-step of solution. The same rotor model is used with the conventional floating ring bearing system where, the bearing forces are provided as displacement dependent time-varying oil and floating ring forces. As a practical environmental condition, the effect of temperature on the viscosity is studied using Dowson equation. The dynamic responses are illustrated both for rotor supported on both gas-foil and floating-ring type bearings. The effects of changes in bearing clearances on the overall dynamic characteristics of the rotor are reported. In order to utilize the gas foil bearing model, an identification study is performed to predict the operating clearance and air viscosity using dynamic response data.

Commentary by Dr. Valentin Fuster
2017;():V002T05A023. doi:10.1115/GTINDIA2017-4735.

Successful demonstration of safety of aircraft engines during extreme events such as Foreign Object Damage and Containment are mandatory for FAA (Federal Aviation Administration) certification. According to FAA every engine has to undergo fan blade out tests and engine has to contain this event without leading to major hazard to aircraft and loss of life. The fan blade out containment test involves the intentional release of a fan blade when the engine is running at full power. The released blade must not pierce or fracture the engine cases during the impact and which in turn can cause damage to the aircraft.

The current trend in the industry is to minimize tests through analytical simulations and demonstrate compliance to regulations and flight-safety requirements. Accurate simulations of such events save significant effort, time and cost. This paper presents the various simulation techniques to demonstrate fan case containment when subjected to fan blade out event. The modeling is carried out with simplifications and assumptions to minimize problem size and maximizing the accuracy in simulation. Various simulation techniques analyzed in this study are used to assess the modeling approach and parameters influence on the event simulation. The effect of rotor imbalance on blade failure and blade kinetic energy are also studied in this paper. LS-DYNA has the capability to perform implicit and explicit methods which is used to analyze the blade out event in this study.

Topics: Blades
Commentary by Dr. Valentin Fuster
2017;():V002T05A024. doi:10.1115/GTINDIA2017-4749.

Squeeze-film-dampers (SFDs) used to couple rotor dynamic systems to linear static structures, such as those in aircraft engines and turbochargers, are often approximated as linear connections in dynamic simulations. Linearized stiffness and damping coefficients of the SFDs can be reasonably estimated for circular centered orbits. Selection of linearized properties for the SFD is challenged under more general whirling conditions, such as those occurring in non-centered dampers with steady gravity loading. In this paper, an efficient method for coupling the rotor system to a static structure modeled as frequency-response-functions (FRFs) through nonlinear SFDs is illustrated. The harmonic balance method (HBM) with arc length continuation technique is employed in the frequency domain to obtain the system periodic response. Degrees-of-freedom participating in the non-linear SFD model, when separated from the remaining linear degrees-of-freedom, are expanded in terms of Fourier coefficients. The algorithm allows the Fourier coefficients approximating the nonlinearity to be iteratively determined at each frequency of interest. The approach has a tremendous time advantage over a traditional nonlinear transient analysis. The method can be used to efficiently predict vibration response on the engine static structure to typical imbalance on the rotors to assess the risk of meeting the low vibration requirements typical of new designs. The prediction includes the primary driving frequencies and their harmonics in the vibration estimate. A flexible rotor system connected to structure through an SFD is used to demonstrate the approach and discuss the impact of results.

Commentary by Dr. Valentin Fuster
2017;():V002T05A025. doi:10.1115/GTINDIA2017-4761.

Dovetail slots are essential structural cut-outs made in compressor disc to assemble blades. Under in-service centrifugal loading and inherent vibrations, the root regions of these dovetail slots are prone to fatigue failures. Surface treatment methods like shot peening, low plasticity burnishing and laser shock peening are employed to achieve fatigue life extension of dovetail slots. Another method commonly employed in aerospace industry for fatigue life extension of circular holes is the cold expansion process. This cold expansion process is a proven surface treatment method capable of achieving highest fatigue life enhancement benefits compared to other surface treatment methods, particularly for circular holes. Considering the efficacy of circular hole cold expansion process, an attempt is made in this work to study the suitability of cold expansion process for dovetail slots.

In this work, a three dimensional, non-linear Finite Element simulation has been carried out to explore the application of cold expansion process for dovetail slot of a compressor disc. This Finite Element simulation involves two main steps namely, cold expansion of holes and machining process between holes. Two circular holes of appropriate radius at root locations of dovetail slot are cold expanded to introduce beneficial compressive residual stresses and further, portion between the two holes is machined-off to obtain the required dovetail shape. Complete distributions of beneficial compressive residual stresses retained after machining of dovetail slot are captured to assess the efficacy of cold expansion. The predicted results indicate that the proposed cold expansion process for dovetail slots is capable of significantly enhancing the fatigue life of dovetail slots.

Topics: Compressors , Disks
Commentary by Dr. Valentin Fuster
2017;():V002T05A026. doi:10.1115/GTINDIA2017-4772.

This paper presents the numerical modeling of a twisted stiffened cylindrical shell employing finite element approach to investigate the transient response due to impact of multiple masses, wherein the shell and the stiffener are modeled as 8 noded isoparametric shell element with five degrees of freedom per node and 3 noded isoparametric curved beam element having four degrees of freedom per node, respectively. The stiffener element is considered as a discrete beam element and its nodal degrees of freedom are transferred to the corresponding degrees of freedom of the shell element considering curvature and eccentricity. The impact force is predicted by employing modified Hertzian contact law relating the contact force to local indentation. As indentation takes place the impactor induces damage and permanent deformation in the contact zone of stiffened panel, as a result the loading and unloading curves are different. Different mathematical equations are considered for both loading and unloading cases in the stiffened panel during low-velocity impact. The accuracy and effectiveness of the finite element approach is verified by comparing the results with the corresponding solutions of analytical as well as standard computational methods available in the open literature. The optimum design of a structure can only be obtained by understanding the impact behavior and the roles of various parameters affecting the response. Hence, parametric study has been carried out to predict the time histories of contact force, displacement of the impact point and in-plane stresses during low-velocity concurrent/delayed impact at multiple locations of the stationary and rotating stiffened shell.

Commentary by Dr. Valentin Fuster
2017;():V002T05A027. doi:10.1115/GTINDIA2017-4774.

This paper presents a comparative analysis of the time, frequency and time-frequency domain based features of the vibration and current signals for identifying various faults in induction motors (IMs) using support vector machine (SVM). Four mechanical faults (bearing fault, unbalanced rotor, bowed rotor and misaligned rotor), and three electrical faults (broken rotor bars, stator winding fault with two severity levels and phase unbalance with two severity levels) are considered in the present study. The proposed fault diagnosis consists of three steps. In the first step, the vibration in three orthogonal directions and the current in three phases are acquired from the healthy and faulty motors using a machine fault simulator (MFS). In second step, useful statistical features are extracted from the time, frequency and time-frequency domain (continuous wavelet transform (CWT)) of the signal. For the effective fault diagnosis, SVM parameters are optimally selected based on the grid-search method along with 5-fold cross-validation, and the effective fault features are selected based on the wrapper model. Finally, the fault diagnosis of IM is performed using optimal SVM parameters and effective features as input to the SVM. The classification performance of all methodologies developed in three domains is compared for various operating conditions of IMs. The test results showed that the developed methodology could isolate ten IM fault conditions successfully based on features from all three domains at all IM operating conditions; however, time-frequency features give the best results.

Commentary by Dr. Valentin Fuster
2017;():V002T05A028. doi:10.1115/GTINDIA2017-4779.

Impact events are very high speed and short duration events. Experimental analysis of such events tends to be extremely expensive and challenging to study because of the apparatus and measurement systems required to capture the event. Due to this, impact events are studied extensively through simulations. The ability to simulate these events is a dictating factor for developing better and more efficient designs.

Traditionally, loads occurring due to impact events are assumed to monotonically increase and hence pure isotropic strain hardening is sufficient to model the material behavior. However, this assumption doesn’t hold true for all impact events. When the loads caused by an impact do not monotonically increase but instead oscillate causing tension and compression cycles, pure isotropic hardening could lead to unrealistic results.

In this work, different strain hardening rules are studied and analyzed for a plate under impact loading. The process to obtain a parameter which sets a realistic combination of isotropic and kinematic strain hardening rules is demonstrated and discussed. Limitations of the existing practice of using isotropic hardening in impact loading cases are studied. An alternative approach to accommodate the kinematic hardening rule into material models using LS-DYNA, a finite element solver, is discussed.

Commentary by Dr. Valentin Fuster
2017;():V002T05A029. doi:10.1115/GTINDIA2017-4781.

In the last few decades, intensive research has been carried out on viscoelastic materials. Among them, most importantly polymers and composites thereof find extensive applications in engineering structures and rotors primarily due to quite high strength to weight ratio in comparison with metals. In dynamic modeling of rotor bearing system, incorporation of damping is very important as stationary (external) damping always helps in stability, however rotary damping (internal) promotes instability of rotors above a certain speed. Therefore for modeling point of view, it is very important to consider both internal or external damping effect. For this reason, the dissipation mechanism has been handled in such a way that it provides proper forces irrespective of its presence in a stationary or a rotary frame. Also in present work, both classical method and operator multiplier method are suggested to derive the equations of motion. The analysis also shows the stability zones of the rotor bearing system for various parametric values of different viscoelastic supports. It is found that choosing a right viscoelastic support can increase the stability criteria of the system to some extent.

Topics: Stability , Bearings , Rotors
Commentary by Dr. Valentin Fuster
2017;():V002T05A030. doi:10.1115/GTINDIA2017-4837.

In design of components, it is more convenient to analyze the component alone by modeling all the interface loads / displacements as boundary conditions rather than modeling the entire assembly. This process of analyzing at component level is referred as sub model analysis. Most of the assembly level model consists of several components and each component may have different owners. In cases where the entire assembly level model cannot be shared with component owners due to confidentiality, Sub model analysis is the preferred approach. Sub-model analysis also reduces overall model size and in turn the solution time.

Sub modeling is widely used approach in static structural analysis. In dynamic analysis, response of any system is a function of its stiffness, damping and inertia properties along with the applied loads. Sub model will have different inertia, stiffness and damping representations when compared with the assembly level model (also known as full model). The effect of these differences on sub model responses compared to full model needs to be investigated to validate sub modeling approach in dynamic analysis.

In this paper it is shown mathematically and also using finite element analyses that the dynamic response of a component is same between sub-model analysis and full model analysis. In sub-model analysis, dynamic behavior of the remaining system is captured by applying interface loads at component interfaces (with remaining model) which in turn is obtained from full model analysis. Frequency domain finite element model with harmonic excitations is considered to validate the sub modeling approach in dynamic analysis. The observations and conclusions inferred from this frequency domain analysis are also applicable for time domain analysis.

This study is carried out using MSC Nastran.

Commentary by Dr. Valentin Fuster
2017;():V002T05A031. doi:10.1115/GTINDIA2017-4846.

In this article, the transient responses of the laminated composite sandwich plate structure are obtained numerically using the commercial finite element package to reduce the computational cost without hampering the accuracy. The plate structure is discretized using the available shell element (SHELL281) from ANSYS library. In order to compute the responses, an ANSYS parametric design language code has been developed based on the finite element steps and Newmark integration technique. The model accuracy and stability have been checked and few numerical examples have been solved. Finally, the effect of different parameters like side-to-thickness ratios, core-to-face thickness ratios, and lamination schemes are computed to show the necessary influences on the time-dependent deflection of the laminated composite sandwich structure.

Commentary by Dr. Valentin Fuster
2017;():V002T05A032. doi:10.1115/GTINDIA2017-4847.

In the present article, the dynamic behaviour of the delaminated composite plate subjected to blast loading has been investigated. For the investigation, a general finite element model using higher-order mid-plane kinematics has been developed. The model has been discretised using nine noded isoparametric Lagrangian elements having nine degrees of freedom at each node. The continuity in the laminated and delaminated section has been established using the intermittent continuity condition. The final governing equation has been solved by applying Newmark’s time integration scheme in conjunction with finite element steps. Further, the said responses have been evaluated by developing an in-house MATLAB code based on the proposed model. In order to illustrate the consistency and accuracy of the present model, convergence and comparison study has been conducted i.e. the responses are evaluated for different mesh sizes and compared them with those of responses of earlier published literature. Finally, various examples have been solved to illustrate the influence of the size and position of debonding, side to thickness ratio, aspect ratio and end condition on the dynamic response of composite structure and discussed in detail.

Commentary by Dr. Valentin Fuster
2017;():V002T05A033. doi:10.1115/GTINDIA2017-4850.

In the present work, analysis of a nonlinear active vibration absorber is carried out by time delay acceleration feedback. The primary system consisting of spring, mass and damper is subjected to multi harmonic and parametric excitation. It is proposed to reduce the vibration of both the primary system and the absorber by attaching a lead zirconate titanate (PZT) stack actuator connected in series with a spring in absorber configuration which act as an active vibration absorber. Due to the external excitation on the primary mass strain is developed in the PZT sensor, which produces voltage and this voltage converted to a counter acting force by the PZT actuator to suppress the vibration of the primary system. Second order method of multiple scales (MMS) is used to obtain approximate solution of the system to study frequency responses for simultaneous primary resonance, principal parametric and 1:1 internal resonance conditions. The analysis is performed for the mass ratio of 0.01 between the absorber and the primary mass.

Commentary by Dr. Valentin Fuster
2017;():V002T05A034. doi:10.1115/GTINDIA2017-4852.

In the present paper Reynolds equation of lubrication under micro-polar fluid for journal bearing is solved by direct-integration method under infinitely long and infinitely short journal bearing assumptions [1]. Infinitely long-bearing and infinitely short bearing solutions are the two available approximate closed form solutions for journal bearings. In the present investigation, solution of Reynolds equation i.e. pressure profile is compared with pressure profile obtained by previously used approximate method like finite difference method (FDM). Mentionable here that any approximation method needs lots of calculation and computer programing to get the result. In the present work it has been found that direct-integration method leads the almost same result as the conventionally used complex finite difference method. CFD analysis is also presented in the present work to justify the profile obtained by direct numerical method. It has seen here that theoretical and simulation results are in good agreement to each other’s.

Commentary by Dr. Valentin Fuster
2017;():V002T05A035. doi:10.1115/GTINDIA2017-4906.

Pressure probes are typically used to measure the pressure of a fluid stream. These probes are designed to serve for 25 years life under operating pressure and temperature conditions. Therefore, such pressure probes are also designed for safe creep behavior. Typically creep is time dependent phenomenon and it can be classified as Primary, Secondary and Tertiary creep. In the literature, the creep phenomenon is studied analytically and numerically. Literature review reveals that creep analysis requires special material models and its selection depends on operating conditions. This work presents FEA based probabilistic design and analysis of pressure measuring probes using ANSYS which has several creep models depending on type of creep phenomenon. Probes in this study are subjected to primary and secondary creep. Therefore, this work proposes combined time hardening creep model. Combined time hardening model has 7 coefficients. This further increases the complexity of the model. Apart from the model complexity, there are various other design and operating parameters which further complicates the creep behavior. Some of the important design and operating parameters are length, diameter and tip dimensions along with pressure and temperature. Thus there are around 16 parameters which controls the creep behavior of pressure measuring probe. Traditional design process of probe is based on deterministic analysis which involves the use of safety factors as a way of accounting for uncertainty in design input parameters. This can often results in overly conservative designs. Moreover, to understand optimal creep behavior of probes under several uncertainties in input parameters becomes a challenging. Therefore, this work presents probabilistic approach as opposed to a deterministic approach to understand the combined effect of several uncertain parameters on creep behavior of probes. This work not only determines probability of probe failure more accurately but also determines the sensitivity of each parameter during creep phenomenon using FEA.

Topics: Pressure , Creep , Design , Probes
Commentary by Dr. Valentin Fuster

Renewable Energy (Solar, Wind)

2017;():V002T06A001. doi:10.1115/GTINDIA2017-4554.

In the past, various influencing parameters of the conventional semicircular-bladed Savonius rotor such as overlap ratio, aspect ratio, number of rotor blades have been optimized through numerical and experimental investigations to improve its performance. Furthermore, the rotor performance under the influence of various blade profiles, shaft, endplates, and augmentation techniques has also been studied. Recent rudimentary studies with an elliptical-bladed Savonius rotor have demonstrated its potential to harness the wind energy more efficiently; however, its influencing parameters have not been thoroughly studied and therefore they need to be optimized to arrive at a suitable design configuration. In view of this, the objective of the present investigation is to optimize the number of elliptical blades on the rotor and then to find the influence of shaft with the optimized number of blades on the rotor performance. For this, 2D unsteady simulation is carried out with different combinations of blades, and after having optimized the number of blades, the influence of shaft on the rotor performance is studied. The continuity, unsteady Reynolds-Averaged Navier-Stokes (RANS) equations, and two equation eddy viscosity SST (Shear Stress transport) k-ω model are solved by using the commercial FVM based solver ANSYS Fluent. The torque and power coefficients are calculated as a function of tip speed ratio (TSR) and at rotating conditions. The total pressure, velocity magnitude, turbulence intensity and streamline patterns are obtained and analyzed to arrive at the intended objective. The numerical investigation demonstrates an improved flow characteristics and performance coefficients of the 2-elliptical-bladed profile without shaft.

Commentary by Dr. Valentin Fuster
2017;():V002T06A002. doi:10.1115/GTINDIA2017-4559.

The continually increasing demand for electricity, cooling and heating accompanied by depleting energy sources, makes it inevitable to use the technologies to harness the available resources to their maximum capacity. The tri-generation systems are the advanced and popular technological option for efficient, reliable, flexible, and less polluting alternatives to utilize the conventional energy resources in an optimal way. In this work, the energy available with conventional fuel is utilized along with solar energy collected through parabolic trough collectors which are integrated with steam injected gas turbine cycle for combined power, heating and cooling requirements. Here a thermodynamic model has been developed for the considered tri-generation combined cooling, heating, and power (CCHP) system and the detailed energy and exergy analysis is performed. The results obtained, by the thermodynamic modeling and analyses of CCHP system based on the first and second law of thermodynamics have been presented and conclusions are drawn from their analysis. This work provides the energy efficient solution for combined heating, cooling, and power for medium load in community usage which may require plant size in the range of 10–50 MW. However, the cost effectiveness depends on the relative cost of gas turbine fuel with respect to other alternate systems with alternate fuels.

Topics: Cooling , Exergy , Heating
Commentary by Dr. Valentin Fuster
2017;():V002T06A003. doi:10.1115/GTINDIA2017-4566.

In this paper, feasible geographical locations in India have been identified to meet a desired performance criterion from a Savonius wind turbine rotor involving semicircular blades. The identification is based upon the average wind speed prevailing at the relevant location. For a given turbine geometry, in order to simultaneously satisfy the required power and torque characteristics over a particular range of tip speed ratio, an inverse problem is solved with the aid of golden section search method (GSSM)-based optimization algorithm to predict the required local wind speed. For this, the minimization of the sum of least square errors between the target power and torque coefficients is done with respect to some initially-guessed power and torque values. Thereafter, based on the estimated wind speed, the reconstructed power and torque characteristic curves are validated with the experimental wind tunnel data. The necessary blockage corrections have been considered during the inverse analysis for which pertinent correlations reported in the available literature are used. The variations of the estimated parameter and the pertinent objective function are studied at different iterations of the GSSM. The effect of the initial guess on the estimated value of wind velocity is also reported and it is found that a unique solution occurs for a particular set of power and torque characteristics. The present work avoids the conventional hit and trial method based nonlinear analysis along with repetitive field tests which are otherwise needed to simultaneously generate a given power and torque performance from the Savonius wind turbine. The proposed inverse method thus can be extremely useful to determine the feasible Indian geographical locations directly from any required torque and power data.

Commentary by Dr. Valentin Fuster
2017;():V002T06A004. doi:10.1115/GTINDIA2017-4572.

With the rising level of greenhouse gas emissions and fuel prices, the hydrokinetic turbines have become increasingly popular for electricity generation in rural and remote areas teemed with small river streams. Such lift-based helical-bladed hydrokinetic turbines were invented over a decade ago, however, they could not find their wide application in commercial power generation. The present investigation deals with the in-situ experiments of a double-step three-bladed helical hydrokinetic turbine for possible electricity generation. Further, its performance is compared with that of a conventional single-step helical-bladed turbine. The main parameters that influence the performance of a helical-bladed hydro turbine are solidity ratio, blade wrap ratio, helix angle, blade profile and number of blades. In the present work, the helical NACA 0022 bladed turbines with solidity ratio of 0.20 and blade wrap ratio of 1.0 have been developed. The developed single and double-step configurations have been field-tested in the Brahmaputra river and their performance characteristics are estimated at different mechanical loading conditions using mechanical dynamometer.

Commentary by Dr. Valentin Fuster
2017;():V002T06A005. doi:10.1115/GTINDIA2017-4603.

This research work summarizes the study of the structural analysis of shear webs (present in wind turbine blades, sometimes also called as spars) with holes. The webs are sandwich composite structures which are supposed to carry the shear loads coming from the wind pressure and the holes are necessary for non-structural requirements of the wind turbine.

The shear webs are strong structures and it is tough to test them to failure in the lab. Hence a structural representative component with lesser dimensions has been tested in the lab to accommodate the capability of the test machines.

However, this component test results cannot be directly used in the wind turbine blade structural verification as the web size is much larger in real life.

A finite element model is developed to simulate the test specimen and its failure behavior. The concept in this modelling approach is to prepare a digital copy of the actual specimen which will follow the same load-displacement behavior and can predict the same failure as seen in the test coupon.

The finite element model is verified for failure using known failure criteria for composite sandwich structures as well as with analytical calculations. This makes sure that the finite element model is a good ‘digital twin’ and simulates the test component behavior one to one. Later, this finite element model is extended to the size of the actual web structure (a family of FE models with different dimensions) to scale up the failure prediction to actual stiffness level.

Commentary by Dr. Valentin Fuster
2017;():V002T06A006. doi:10.1115/GTINDIA2017-4645.

The Vortex Generators located over the airfoils are generally small in size. Due to its small size and shape, the mesh requirements are high and mesh generation becomes complex. In this study, the source term modelling approach termed as BAY model developed by Bender et al. is used to simulate the effect of Vortex Generators. One of the advantages of BAY model is its simplicity eliminating the complex grid requirements around the Vortex Generator for the Computational Fluid Dynamic simulations. Comparing with the BAY model approach, mesh resolved Vortex Generator approach will need more number of cells in the domain. Hence using the B AY model is advantageous in computational cost also.

The solver EllipSys3D, which is an incompressible structured multi-block finite volume based RANS (Reynolds Averaged Navier-Stokes) solver, is used for the studies. Parametric studies using BAY model are carried out for different heights, lengths, chord wise locations and spacing of Vortex Generators on a wind turbine airfoil. The qualitative results predicted using BAY model are in lined with experimental results from literature showing that it is capable to mimic the effect of Vortex Generators. So overall due to its simplicity source term modelling through BAY model can be used for quick parametric studies.

Commentary by Dr. Valentin Fuster
2017;():V002T06A007. doi:10.1115/GTINDIA2017-4675.

The importance of renewable energy has increased continuously in the recent years due to the growth in the energy demand and a decrease in the fossil fuel resources. Harnessing the low rated wind energy is the promising source so that the wind turbine can be used all year round. Deploying sequence of small turbine is efficient than single bigger size turbine in extracting the low rated wind energy. Hence, in this work, sequence of small vertical axis wind turbine is arranged in the tree like structure and named it as wind tree. The vertical axis type of turbine would be able to perform more efficiently at minimum wind velocity. So, the Helical Savonius vertical axis rotor is deployed in the wind tree which gives the relatively high torque and self-starting even at low wind speeds. The main aim of this work is to analyze numerically the cluster of vertical axis wind turbine in order to improve the average output of the wind tree. In this study, the vertical axis turbines are arranged in the branches of the tree at different plane, so that the wake of one turbine will not affect the turbine in the downstream. The numerical simulation has been studied by using commercially available software ANSYS CFX©. The single helical vertical axis wind turbine is fabricated and tested in the open jet wind tunnel and this experimental result is used for validating the numerical results. In addition to the validation, sensitive study for the grid and the turbulence model has been carried out to improve the simulation quality. Vertical axis wind can accept wind from any direction without any yaw mechanism, so the average performance of this type of turbine in cluster is analyzed by changing the flow (α = 0°, 45° and 90°) of the wind turbine cluster. It is observed from this study that the average power coefficient of the cluster of turbine at the flow angle of 45° has better performance than the other pattern. Moreover, its average power coefficient is 2.3 times higher than the isolated vertical axis wind turbine. These results of the cluster simulation are used to develop an efficient wind tree to harness the low rated wind energy.

Commentary by Dr. Valentin Fuster
2017;():V002T06A008. doi:10.1115/GTINDIA2017-4784.

For food preservation, drying techniques is most widely used. Earlier drying was done openly in sun. But now with increased awareness, drying of agricultural produce is done with care. Greenhouse dryers are being mostly used. Good greenhouse dryers are considered one which can dry products in short span of time. For obtaining good quantity of dried products, the design of greenhouse dryer should be such that the air circulation is good and high temperature can be achieved near the crops. In present work, Computational Fluid Dynamics (CFD) approach has been used to visualize the air flow pattern and temperature distribution near the crops i.e., inside the direct type greenhouse dryer. Experimentally obtained data has been used as boundary conditions and numerically obtained results are helpful in understanding local parameters which cannot be found out experimentally.

Commentary by Dr. Valentin Fuster
2017;():V002T06A009. doi:10.1115/GTINDIA2017-4815.

The interest in sustainable forms of energy is being driven by the anticipated scarcity of traditional fossil fuels over the coming decades. There is also a growing concern about the effects of fossil fuel emissions on human health and the environment. Many sources of renewable energy are being researched and implemented for power production. In particular, wind power generation by vertical-axis wind turbines is one of the option often considered. This option offers a robust design because of the relative simplicity of its technology. However, it also presents challenges that are inherent to its very concept. These systems suffer from dynamic stall, noticeably one of the main causes of the loss of performance. A dual-element concept is proposed as a way of alleviating the losses due to the dynamic stall. An economic analysis is done to establish the economic viability of the model. The Great Coast of Senegal is selected as a site of operation in this study.

Commentary by Dr. Valentin Fuster

Inlets and Exhausts

2017;():V002T07A001. doi:10.1115/GTINDIA2017-4598.

Single stage gas guns are typically used for accelerating the projectiles in bird and hail impact tests of aerospace components and engines. In this paper an alternative design for single stage gas gun is studied, which is derived from V3 canon. Three dimensional numerical simulations is carried out for the optimal secondary connection angle with the main barrel. A one dimensional code is developed for the V3 canon based design. Design of experiments conducted to find the response surface for the optimal location of the secondary connection, volume and pressure of the secondary tank.

Commentary by Dr. Valentin Fuster
2017;():V002T07A002. doi:10.1115/GTINDIA2017-4623.

Gas turbine engines operate under varying conditions. Subsequently, thrust varies under diverse conditions. Owing to combustion the exhaust runs full. The flow jets have been in utilization for engineering systems, present work investigates the merits of jet perforations for gas turbine engine applications. Controlling thrust when device is running is not an option in the present world. This led us to do the study on the flow of jet through various perforated shapes. At present, thorough experiments are carried out for flow analysis of diverse jet perforations and related flow optimization for better performance. Experiments are carried out on a scaled cascade tunnel. The perforations are of circle, square, triangle and ellipse in shape. The physical insight from this work would be very informative and useful for gas turbine engine operations. Systematic experiments are carried out to fundamentally understand flow behavior with different perforations at the exit. Gas turbine engines have revolutionized the propulsion systems. The very idea of generating large amount of thrust from a small volume has always intrigued scientific community about the effectiveness of operations. Though, the engine works, however, effectiveness have always been questioned and worked upon. Results significantly state that jet perforations do modify the flow jet characteristics. The results show the increase in velocity by 6.2% on using the circular perforation. For the circular perforation wall jet, velocity increases by 14.7% with respect to reference jet i.e. jet without perforation.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2017;():V002T07A003. doi:10.1115/GTINDIA2017-4699.

Jet blast impact on aerofoil blade of the deflector is studied which redirects the high energy exhaust of jet engine during the ground testing. The geometric model of aerofoils is designed with structured mesh around the aerofoil in rectangular domain generated in ICEM 16 software. The jet blast impact on aerofoil blade of the deflector is numerically simulated with SST k-ω model based on CFD theory. The fluid flow is high-speed compressible flow and flowing fluid air is considered as an ideal gas and also Sutherland’s law viscosity is applied to account for the dependence of molecular viscosity on temperature. Flow is taken as first order upwind and flux type is AUSM (Advection Upstream Splitting Method) to get an exact resolution of contact and shock discontinuities. The distribution of temperature, pressure, velocity and streamline of fluid flow is numerically simulated by FLUENT 16 software and layout of eddies generation behind aerofoil is generated in Tecplot 360 software. The coefficient of lift (Cl) and the coefficient of drag (Cd) are calculated to study the impact on aerofoil blade in horizontal and vertical direction. The result indicates that the method presented in this paper can analyze the fluid behavior on the complicated geometry of aerofoil blade that the flow between two adjacent aerofoil blades obtains a highly reliable simulation result. The value of lift force is negative i.e it holds the deflector towards the ground, so optimum balance between drag force and lifts force is obtained by simulating at a different angle of attack and pitch. Through CFD numerical simulation at a different angle of attack and pitch, the best result is obtained and conductive suggestions can be given for the adaptation of the JBD blade.

Commentary by Dr. Valentin Fuster

Emerging Technologies (Hybrid Electric Propulsion, UAV, ...)

2017;():V002T08A001. doi:10.1115/GTINDIA2017-4643.

This paper aims to design, build, fabricate and test an aeroamphibious unmanned vehicle which can operate on air and water. Typically, an aeroamphibious unmanned vehicle is a vehicle which has the potential to operate in air, water as well as on the land and can adapt to both aerial, aquatic as well as terrestrial conditions. The vehicle is embedded with various sensors which gives live data to the ground station. Non availability of technology, dynamics of unmanned vehicle inside water, on the air and surface, complexity of electronics and communication are the main shortcomings which are highlighted in this paper. The undeveloped performance of the vehicle is mainly due to non-availability of technology and complexities of design. The only way to overcome these difficulties are to merge many existing technologies into one.

Commentary by Dr. Valentin Fuster

GT Operation and Maintenance

2017;():V002T09A001. doi:10.1115/GTINDIA2017-4544.

Evaluation of engine performance during armament firing in fighter aircraft is a vital qualification aspect for airframe engine integration. Ingestion of missile’s efflux into air intake results in rapid increase of engine inlet temperatures (temperature ramps) which cause flow disturbance to the compressor. Temperature distortion caused due to armament firing and its effect on compressor stability during flight testing is evaluated. Accordingly mitigation actions are recommended for stall/surge free operations. Distortion descriptors are assessed using simulation model (engine performance program) and results compared with engine distortion limits.

Commentary by Dr. Valentin Fuster
2017;():V002T09A002. doi:10.1115/GTINDIA2017-4841.

Diagnosis, isolation and corrective action of incipient faults in a developmental Aero Gas Turbine Engine, mandates advanced warning of the emerging faults by apt and timely degradation monitoring in order to mitigate catastrophic failure. This calls for cautious performance monitoring during the test runs by instrumenting the engine under test with multiple sensors to acquire the physical parameters like temperature, pressure, flow and speed which are indicative of the engine degradation. Sensor reliability is critical to engine control and performance monitoring. Sensor data which serves as the primary key for assessing the engine behaviour needs to be validated before its use in determining the degradation. Particularly in a developmental engine under test, the accuracy and reliability of measurements creates the basis for understanding the engine behaviour, in order to evaluate its performance. This paper targets to develop validation tool to ensure that only trusted sensor measurements are used for engine performance computation by weeding out the erroneous data. The pre-processing of data to ensure its accuracy also serves as a “need for maintenance indicator” to warn the operator for sensor breakdowns, wearing or deterioration and detect calibration needs. Development and validation of the LabVIEW based “Sensor Data Validation Tool (SDVT)” using the actual test run data constitutes the main body of this paper along with concluding remarks which brings out the validation results and the required maintenance action.

Topics: Sensors , Gas turbines
Commentary by Dr. Valentin Fuster

Materials and Manufacturing (Including Coatings, Composites, CMCs, Additive Manufacturing)

2017;():V002T10A001. doi:10.1115/GTINDIA2017-4514.

Short fiber-reinforced polymer composites are used in numerous tribological applications. In the present work, an attempt has been made to improve the wear resistance of short glass fiber (SGF) reinforced polypropylene composites by incorporation of micro-sized Linz-Donawitz slag (LDS) particles. Composites with different LDS content (0, 7.5, 15 and 22.5 wt%) in a polypropylene matrix base with 20 wt% SGF reinforcement are prepared by injection molding technique. Solid particle erosion trials, as per ASTM G76 test standards, are conducted on the composite samples following a well-planned experimental schedule based on Taguchi design-of-experiments. Significant process parameters predominantly influencing the rate of erosion are identified. The study reveals that the LDS content and impact velocity are the most significant among various factors influencing the wear rate of these composites. Further, a prediction model based on artificial neural network (ANN) is proposed to predict the erosion performance of the composites under a wide range of erosive wear conditions. This work shows that an ANN model is quite helpful in saving time and resources that are required for a large number of experimental trials and thus, successfully predicts the erosion rate of composites both within and beyond the experimental domain.

Commentary by Dr. Valentin Fuster
2017;():V002T10A002. doi:10.1115/GTINDIA2017-4611.

This paper investigates on the problem of functionally graded (FG) shallow conical shells subjected to low-velocity impact by a solid spherical mass at the centre. Turbomachinery blades with low aspect ratio could be idealized as twisted rotating cantilever FG shallow conical shells. An analytic solution method is developed to solve and predict the impact response in terms of contact force, impactor displacement, initial velocity of impactor, target displacement and indentation of the FG conical shells with different sigmoidal power law exponent. A modified Hertzian contact law considering permanent indentation is used to calculate the contact force along with other impact response parameters. Using the Newmark’s time integration scheme the time dependent equations are solved. An eight noded isoparametric shell element is considered for the present finite element model. Parametric studies are performed to study the effects of triggering parameters like initial velocity of impactor (VOI), mass of the impactor (M0) and twist angle (Ψ) considering different sigmoidal power law exponent (N) for Ni (Nickel)-ZrO2 (Zirconia) and Ti (Titanium alloy-Ti–6Al–4V)-ZrO2 (Zirconia) functionally graded conical shell subjected to low velocity impact.

Commentary by Dr. Valentin Fuster
2017;():V002T10A003. doi:10.1115/GTINDIA2017-4613.

Additive manufacturing (AM) via the direct metal laser sintering (DMLS) route is a new technology for both new make and repair application in gas turbine hot gas path components. This paper presents the development of a new oxidation coating Ceral 10 as a protective coating on the AM CoCrMo alloys. A high Al activity slurry aluminide coating (Ceral 10) was deposited on the DMLS CoCrMo. The coating produced on DMLS CoCrMo was uniform and intact having a thickness of ∼ 80–100 μm. The slurry aluminide coating showed an Inward diffusion with the DMLS CoCrMo substrate having an Al of 38–40 wt% and Si (12–13 wt%) after the diffusion heat treatment. The interface with the substrate was gradual in terms of chemistry with an interdiffusion zone of 15–20 μm. The Ceral10 coating showed limited oxidation up to 1038°C (1000 h) and at 1066°C (after 500 h), coating spallation occurred. The distinct thermally grown oxide between the coating-substrate interface led to the spallation. The effectiveness of the Ceral 10 coating to protect the DMLS CoCrMo alloy at high temperatures is evaluated via detailed microstructural characterization.

Topics: Coatings , oxidation
Commentary by Dr. Valentin Fuster
2017;():V002T10A004. doi:10.1115/GTINDIA2017-4614.

Additive manufacturing via the direct metal laser sintering (DMLS) route is an attractive technology for repair and refurbishment of gas turbine components. This paper presents the study of the role of various process parameters such as laser power, scan speed, layer thickness and powder variability in obtaining dense, pore-free parts of CoCrMo using the DMLS route. The variation in surface roughness of the built samples and the effect of powder variability on the part density were brought out via a systematic design of experiments (DOE). Different solution heat treatments were carried out to establish the recrystallization behavior of DMLS CoCrMo. The variation in microstructure and properties were evaluated between powders from two different sources, EOS and Praxair, as an important aspect towards practical applicability of the process for components.

Commentary by Dr. Valentin Fuster
2017;():V002T10A005. doi:10.1115/GTINDIA2017-4636.

Electrical discharge machining (EDM), a thermo-mechanical machining process, is used in producing a complicated intrinsic cavity in difficult-to-machine materials with excellent surface finish. One of the major disadvantages of EDM process is the tool wear. However, tool wear can be used advantageously for coating purpose. Coating is a unique method of EDM process by the use of electrode prepared through powder metallurgy (PM) route. This process is also cheaper as compared to other deposition processes like chemical vapor deposition (CVD) and physical vapor deposition (PVD) processes. Therefore, electrical discharge coating (EDC) can be employed in industries for coating purpose where the corrosion resistance and hardness of the work piece material are required to be increased for their use in a wide range of environmental condition. Copper (Cu) and tungsten (W) powders in weight percentage of 30 and 70 respectively are used for the preparation of the tool electrode. The PM process parameters like compaction pressure (CP) and sintering temperature (ST) are varied to prepare the tool electrodes. The density and electrical conductivity of the electrodes are found to increase with an increase in compaction pressure and sintering temperature. The substrate on which coating is made is chosen as AISI 1040 stainless steel with EDM oil as the dielectric fluid. During coating, the influence of parameters like discharge current (Ip), duty cycle (τ) and pulse-on-time (Ton) on material deposition ratio (MDR), Average surface roughness (Ra), coated layer thickness (LT) and micro-hardness of the coated layer are studied. To reduce the number of the experiment, Taguchi’s L18 orthogonal array has been used. To find out the best parametric combination that can simultaneously optimize all performance measures, multi-objective optimization on the basis of ratio analysis (MOORA) method combined with Firefly algorithm has been employed.

Commentary by Dr. Valentin Fuster
2017;():V002T10A006. doi:10.1115/GTINDIA2017-4679.

Titanium alloy of grade-5 (Ti6Al4V) and stainless steel of grade AISI 316 have wide applications in various engineering sectors due to their favorable material properties such as low thermal conductivity, high corrosion resistance and high strength to weight ratio. The literature survey suggests that Ti6Al4V and AISI 316 have the similar field of applications and comparative study of both the materials was limited. In the present study, laser drilling of Ti6Al4V and AISI 316 have been performed using Nd:YAG millisecond laser under identical machining conditions. The control parameters considered for the study are laser energy, pulse repetition rate, pulse width and flushing pressure having each at three different levels. To reduce the total number of experimental run and obtain maximum information for the experimental trials, Taguchi’s L27 orthogonal array has been adopted. Further, the study has been focused to understand the behavior based on experimental data on similarities and differences between laser drilling process of Ti6Al4V and AISI 316 are qualitative. The outcome of experiments in terms of circularity of hole and heat affected zone (HAZ) for laser drilled holes are studied. It is observed that HAZ increases with increase in laser energy and pulse repetition rate. It may be due to a higher average power of the laser beam, which is directly proportional to laser energy and pulse repetition rate. Higher the value of laser energy, higher will be the laser thermal energy and higher HAZ. Heat affected zone (HAZ) can be minimized with low laser energy and pulse width during laser drilling of Ti6Al4V and AISI 316. From the study, it is revealed that pulse repetition rate is the most significant parameter in the formation of circularity and HAZ.

Commentary by Dr. Valentin Fuster
2017;():V002T10A007. doi:10.1115/GTINDIA2017-4798.

Laser Additive Manufacturing (LAM) is one of the greener routes for fabrication of Inconel 718 (IN718) components. In the present work, Taguchi L9 array based optimization is performed using grey relational analysis to optimize the process parameters for the fabrication of thin walled structures using a 2 kW fibre laser based additive manufacturing system. Within the framework of the experimental conditions of the study, the LAM processing parameters, i.e., laser power, scan speed and powder feed rate, are optimized for minimum width and maximum height. The optimized parameters are used for the deposition of multi-layered walls and it is subjected to heat treatment at 1000 °C for duration of one-hour, followed by water quenching. Comprehensive investigations on microstructural and mechanical behaviour using optical microscopy (OM), X-ray diffraction (XRD) analysis, micro-hardness and automated ball indentation (ABI) are carried out. Microstructure examinations of LAM deposits of IN718 reveal intermixed dendritic and cellular structures. However, homogenization in microstructure is observed through heat treatment resulting in reduced micro-hardness. It is also observed that there is considerable increase in the crystallite size of the deposits after heat treatment. This study opens a new route for fabrication of thin walled structures using LAM with modified properties by erasing the thermal history through heat treatment.

Commentary by Dr. Valentin Fuster
2017;():V002T10A008. doi:10.1115/GTINDIA2017-4855.

Titanium alloys are gaining widespread acceptance in aerospace industry because of its high specific strength, corrosion resistance and good fatigue properties. Dovetails of the compressor blades, gears, splines etc. are some aerospace components that fail through premature fatigue crack initiation and propagation under the action of wear, fatigue and fretting fatigue. The fretting failure originates from the surface or near surface and leads to the damage of the components. Therefore the surface of components can be modified to improve the tribological performance by plasma nitriding which improve the titanium alloy by forming layer of hard TiN and Ti2N phases on surface. Plasma nitriding of titanium alloys has several advantages over gas and liquid nitriding methods where the phase formation and the depth of nitriding can be controlled. In this study Ti-6Al-4V alloy is taken as surrogate material for gas turbine application and its surface is modified by plasma nitriding at three different temperatures 500, 700 and 800 °C with N2:H2 ratio of 4:1 at 5 mbar pressure for 5 hrs. It is observed from XRD that at 500 and 700 °C temperature, nucleation of ε-Ti2N and δ-TiN started and complete titanium nitride layer formed at 800 °C. Nucleation and growth mechanism was studied by surface and cross section SEM analysis. Nitride layer of around 0.5 μm with ε-Ti2N and around 2 μm thick of both ε-Ti2N and δ-TiN phases were formed at 700 and 800 °C respectively. It is observed that the surface roughness increases with increasing the temperature for plasma nitriding. Vickers microhardness (HV0.1) is observed to be increased from 393.7 HV to 1016.4 HV by plasma nitriding at 800 °C.

Commentary by Dr. Valentin Fuster
2017;():V002T10A009. doi:10.1115/GTINDIA2017-4859.

Components such as bladed rings, and bladed disks fabiricated out of titanium matrix composites were extensively explored in the two decades since about 1990 as light weight replacements for conventional superalloy blades and disks in the intermediate hot stages of gas turbines. One of the challenges, which has hindered their adoption is the relative unreliability of the composite components; nominally identical Ti composite specimen display a much larger variability in strength than their superalloy counterparts.

In the present work, we have quantified the reliability of Ti matrix composites by developing a detailed micromechanical-statistical model of their failure. The micromechanical model resolves fibres, matrix, and the interface, and accounts for such failure modes as fibre breakage, matrix cracking, matrix plasticity, interfacial sliding, and debonding. It also accounts for mechanical interaction between these various failure modes. The mechanical model’s predictions are validated against synchotron X-ray measurements reported in the literature, both after loading, and unloading. Using the detailed micromechanical model, Ti matrix composite was simulated following a Monte Carlo framework. These simulations yield the empirical strength distribution of the Ti matrix composite, and insights into the dominant failure mode. The latter allows the construction of a stochastic model of composite failure. The stochastic model can be used to determine safe working loads as a function of composite size for any desired reliability level.

Commentary by Dr. Valentin Fuster
2017;():V002T10A010. doi:10.1115/GTINDIA2017-4893.

The gas turbine components undergo fatigue load spectrum of variable amplitude loading. In this study, fatigue crack growth rate after multiple cycles of tensile overload has been investigated in Ti-2.77Sn-0.48Cu-1.15Fe-6.61V alloy. The overload at the crack tip produces the plastic zone at the vicinity, which retards the crack growth. Crack growth retardation effect has been studied at 15% and 25% overload percentages to observe its retardation effect. The multiple overloads applied after fixed interval of cycles produces a plastic region around the crack. After reloading the specimen further with constant loading, the crack growth rate is retarded thus causing increase in the fatigue life, which is observed in the graph of crack length vs number of cycles. The microstructure study has been carried out using Scanning Electron Microscope (SEM) and Electron Back Scatter Diffraction (EBSD), which gives qualitative information of strain to characterize the fatigue crack growth. The slope of crack length vs number of cycles before and after tensile peak overload was compared to evaluate the retardation effect at varying overload percentages.

Commentary by Dr. Valentin Fuster
2017;():V002T10A011. doi:10.1115/GTINDIA2017-4894.

The components of the aero engines such as fan blades are generally manufactured from Titanium alloy forgings. At the elevated temperatures, the affinity of Titanium towards oxygen is very high, which results in formation of oxide layer on surface known as alpha-case layer. This alpha-case is both hard and brittle in nature which results in localized micro failure during its application. This gives rise to a fatigue crack initiation zone and compromises the integrity of the component, causing it to fail. To investigate this, Titanium α-β (Ti 64), α (Sn) and β (Mo) alloys were heat treated at 1010°C for 30min, 60min, 90min and 120min followed by air cooling. Formation of alpha-case layer in Ti-6Al-4V, Ti-Sn and Ti-Mo increased from 120.5μm to 391.1μm, 128.77μm to 443.23μm, 105.75μm to 262.46μm at 30mins and 120mins respectively. Chemical treatment, cathodic de-oxygenation, surface coating and laser ablation methods are generally used to remove the alpha case. In the current study, acid pickling is used to remove the alpha case layer, as this process is simple and also easily applicable to any complex shape of the material. In this method, samples were dipped in the solution of HF (5%) and HNO3 (35%) at 80 °C for fixed time at fixed intervals to find the rate of alpha case removal. Micro indentation was carried out to obtain hardness profile from surface to bulk of heat treated specimen. The quantification of alpha case oxide layer from surface to bulk was done by EDS.

Topics: Heat , Titanium alloys
Commentary by Dr. Valentin Fuster
2017;():V002T10A012. doi:10.1115/GTINDIA2017-4900.

DMLS (Direct Metal Laser Sintering), an additive manufacturing technology, is increasingly becoming popular to build intricate high quality functional parts & rapid prototypes. DMLS technology uses a high intensity laser to build components layer by layer, directly from metal powder. CAD data is directly converted to part without the need for tooling. It is possible to build internal features and passages that are not possible in conventional manufacturing routes.

The process generates significant amount of condensate due to vaporization and suction applied to build chamber. Typically as much as 30% of the weight of powder ends up as condensate. The condensate so generated cannot be directly recycled. This results in significant reduction in profitability and process efficiency.

This study pertains to 18% Ni Maraging Steel grade C300, which commonly used in DMLS process. Maraging Steel is used extensively to build functional parts by DMLS process especially for Tool and Die applications.

In the present study chemistry, particle size distribution & morphology of the condensate was studied & compared with the powder. Parts were built using condensate and chemical, physical, mechanical, microstructure and XRD studies were done. These properties were compared with properties of parts built using fresh powder.

No difficulty was encountered in building parts using condensate. However, hardness and tensile properties were found to be inferior, thus it is not possible to recycle the condensate directly.

Present research investigates the cause of difference in these properties.

Commentary by Dr. Valentin Fuster

Analytics and Digital Solutions for Gas Turbines/Rotating Machinery

2017;():V002T11A001. doi:10.1115/GTINDIA2017-4609.

Attaining the design point of any mechanism necessitates undergoing the initial processes satisfactorily. Gas turbine engines used on land, air and water also undergo the initial starting process with the help of external sources. A typical operation cycle of a gas turbine engine consists of zero to idle speed, idle to max speed and max speed to full reheat, the latter being the case for military engine application. It is found that gas turbine engine performance prediction has improved with the usage of computers where the physics of engine behaviour are mathematically coded. The performance prediction software also helps in designing the control systems which governs the engine response to throttle inputs, define the safe operational limits and provide a trouble free automated engine operation during the entire mission. This paper gives an overview of the experimental research work undertaken on compressor and combustor components and engine to improve upon the starting phenomenon since 1950s. The review also looks into the theoretical work undertaken to model the starting process that may help reducing the expensive and time-consuming testing of developmental engine.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
2017;():V002T11A002. doi:10.1115/GTINDIA2017-4706.

Accurate life prediction and monitoring for gas turbine engines has become increasingly important in recent years as commercial aircraft fleets are being offered through guaranteed engine maintenance programs, where plan rates are based on mission profiles, operating environment, operational hours and cycles accumulated. Hence, accurate monitoring and life predictions of critical engine components is associated with a tremendous financial incentive. A state of the art gas turbine engine carries up to 5000 sensors, which can be used to evaluate the performance of the engine. This data can be used to monitor engines in real-time, as well as collecting and analyzing that data after being streamed via satellite during flight, where algorithms can evaluate and prevent technical issues before they occur. The data collected provides engine manufacturers with early warnings related to failure diagnosis, and it enables airlines to schedule engine maintenance efficiently and in a cost effective manner. Due to the nature of the engine’s operational environment, sensors cannot be placed in certain areas of interest inside a gas turbine engine. Furthermore, thermo-mechanical models are often complex and computationally expensive to run in real time. Hence, in this work we describe the development of thermo-mechanical reduced models that can act as virtual sensors, in locations where real sensors cannot survive, and hence approximate damage variables at critical locations on a component of interest, which can be used for real-time diagnostics.

Topics: Gas turbines , Damage
Commentary by Dr. Valentin Fuster

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