0

Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
research-article  
Lukas Schwerdt, Sebastian Willeke, Lars Panning-von Scheidt and Jörg Wallaschek
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041071
A model order reduction method based on the Component Mode Synthesis for mistunend bladed disks is introduced, with one component for the disk and one component for each blade. The interface between the components at the blade roots is reduced using the wave-based substructuring method, which employs tuned system modes. These system modes are calculated first, and used subsequently during the reduction of the individual components, which eliminates the need to build a partially reduced intermediate model with dense matrices. For the disk, a cyclic Craig-Bampton reduction is applied. The deviations of the stiffness and mass matrices of individual disk sectors are then projected into the cyclic basis of interior and interface modes of the disk substructure. Thereby it is possible to model small disk mistuning in addition to large mistuning of the blades.
TOPICS: Modeling, Disks, Blades, Stiffness, Waves
research-article  
Harish Subramanian Gopalakrishnan, Kiran Manoharan and Santosh Hemchandra
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041080
Interaction between coherent flow oscillations and the premixed flame in combustors can result in coherent unsteadiness in the global heat release response. These coherent flow oscillations can either be self-excited or result from hydrodynamic response of the flow field to acoustic forcing. Recent work has focused on understanding the various instability modes and mechanisms that control hydrodynamic instability in single nozzle swirl flows. However, the effect of multiple closely spaced nozzles as well as non-axisymmetric nature of the confinement imposed by the combustor liner on swirl nozzle flows remains unexplored. We study the influence of inter-nozzle spacing and non-axisymmetric confinement on the local temporal and spatiotemporal stability characteristics of multi-nozzle flows in this paper. The base flow model for multi nozzle case is constructed by superposing contributions from a base flow model for each individual nozzle. The influence of flame is captured by specifying a spatially varying base flow density field. We investigate the case of a single nozzle and three nozzles arranged in a straight line within a rectangular combustor. The results show that geometric confinement imposed by the combustor walls has a quantitative impact on the eigenvalues of the hydrodynamic modes. Decreasing nozzle spacing for a given geometric confinement configuration makes the flow more unstable. The presence of an inner shear layer stabilized flame results in an overall stabilization of the flow instability. We also discuss qualitatively, the underlying vorticity dynamics mechanisms that influence the characteristics of instability modes in triple nozzle flows.
TOPICS: Flow (Dynamics), Nozzles, Hydrodynamic stability, Combustion chambers, Flames, Oscillations, Dynamics (Mechanics), Stability, Vorticity, Flow instability, Heat, Acoustics, Shear (Mechanics), Spatiotemporal phenomena, Eigenvalues, Density
research-article  
Kevin McElhaney and Robert Mischler
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041037
Tunnels represent one of the most severe operating conditions for diesel engines in diesel-electric locomotive applications, specifically for non-ventilated tunnels located at high elevation. High ambient air temperatures are observed in these tunnels due to heat rejected from the locomotive engines through the exhaust and engine cooling and lubrication systems. Engine protection algorithms cause the maximum allowable engine horsepower to be reduced due to these conditions leading to a reduction in train speed and occasionally train stall. A first law based model was developed to simulate the performance of a train pulled by GE diesel-electric locomotives equipped with medium speed diesel engines in a high altitude and non-ventilated tunnel. The model was compared against and calibrated to actual tunnel operation data of EPA Tier 2 compliant locomotives. The model was then used to study the impact of engine design changes required for EPA Tier 4 compliant locomotives, specifically the introduction of exhaust gas recirculation (EGR), on engine, locomotive, and train performance in the tunnel. Simulations were completed to evaluate engine control strategies targeting same or better train performance than the EPA Tier 2 compliant locomotive baseline case. Simulation results show that the introduction of EGR reduces train performance in the tunnel by increasing the required reduction in engine horsepower, but is slightly offset by improved performance from other engine design changes. The targeted engine and train performance could be obtained by disabling EGR during tunnel operation.
TOPICS: Modeling, Locomotives, Tunnels, Engines, Trains, Exhaust gas recirculation, Horsepower, Diesel, Diesel engines, Engine design, Exhaust systems, Simulation, Industrial lubrication systems, Algorithms, Engineering simulation, Simulation results, Heat, Temperature, Cooling
research-article  
Simone Cubeda, Lorenzo Mazzei, Tommaso Bacci and Antonio Andreini
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041038
Turbine inlet conditions in lean-burn aeroengine combustors are highly swirled and present non-uniform temperature distributions. Uncertainty and lack of confidence associated to combustor-turbine interaction affect significantly engine performance and efficiency. It is well known that only Large-eddy and Scale-adaptive simulations can overcome the limitations of RANS in predicting the combustor outlet conditions. However it is worth investigating the impact of such improvements on the predicted aerothermal performance of the Nozzle Guide Vanes (NGVs), usually studied with RANS-generated boundary conditions. Three numerical modelling strategies were used to investigate a combustor-turbine module designed within the EU Project FACTOR: i) RANS model of the NGVs with RANS-generated inlet conditions; ii) RANS model of the NGVs with SAS-generated inlet conditions; iii) SAS model inclusive of both combustor and NGVs. It was shown that estimating the aerodynamics through the NGVs does not demand particularly complex approaches, in contrast to situations where turbulent mixing is key. High-fidelity predictions of the turbine entrance conditions proved very beneficial to reduce the discrepancies in the estimation of adiabatic temperature distributions. However, a further leap forward can be achieved with an integrated simulation, capable of reproducing the transport of unsteady fluctuations generated from the combustor through the turbine, which play a key role in presence of film cooling. This work therefore shows how separate analysis of combustor and NGVs can lead to a poor estimation of the thermal loads and ultimately to a wrong thermal design of the cooling system.
TOPICS: Combustion chambers, Reynolds-averaged Navier–Stokes equations, Turbines, Temperature distribution, Simulation, Stress, Fluctuations (Physics), Design, Modeling, Aerodynamics, Cooling systems, Turbulence, Eddies (Fluid dynamics), Engines, Uncertainty, Film cooling, Nozzle guide vanes, Boundary-value problems
research-article  
Giacomo Bonciolini and Nicolas Noiray
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041027
Sequential combustion constitutes a major technological step-change for gas turbines applications. This design provides higher operational flexibility, lower emissions and higher efficiency compared to today's conventional architectures. Like any constant pressure combustion system, sequential combustors can undergo thermoacoustic instabilities. These instabilities potentially lead to high-amplitude acoustic limit cycles, which shorten the engine components' lifetime and therefore reduce their reliability and availability. In case of a sequential system, the two flames are mutually coupled via acoustic and entropy waves. This additional inter-stages interaction markedly complicates the already challenging problem of thermoacoustic instabilities. As a result, new and unexplored system dynamics are possible. In this work, experimental data from our generic sequential combustor are presented. The system exhibits many different distinctive dynamics, as function of the operation parameters and of the combustor arrangement. This paper investigates a particular bifurcation, where two thermoacoustic modes synchronize their self-sustained oscillations over a range of operating conditions. A low-order model of this thermoacoustic bifurcation is proposed. This consists of two coupled stochastically driven non-linear oscillators, and is able to reproduce the peculiar dynamics associated with this synchronization phenomenon. The model aids in understanding what the physical mechanisms that play a key role in the unsteady combustor physics are. In particular, it highlights the role of entropy waves, which are a significant driver of thermoacoustic instabilities in this sequential setup. This research helps to lay the foundations for understanding the thermoacoustic instabilities in sequential combustion systems.
TOPICS: Combustion chambers, Synchronization, Combustion systems, Entropy, Waves, Bifurcation, Dynamics (Mechanics), Acoustics, Engines, Reliability, System dynamics, Pressure, Combustion, Physics, Oscillations, Flames, Design, Gas turbines, Architecture, Emissions, Limit cycles
research-article  
Cody Dowd and Joseph Meadows
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041025
Lean premixed (LPM) combustion systems are susceptible to thermoacoustic instability, which occurs when acoustic pressure oscillations are in phase with the unsteady heat release rates. Porous media has inherent acoustic damping properties, and has been shown to mitigate thermoacoustic instability; however, theoretical models for predicting thermoacoustic instability with porous media do not exist. In the present study, a 1-D model has been developed for the linear stability analysis of the longitudinal modes for a series of constant cross-sectional area ducts with porous media using a n-Tau flame transfer function. By studying the linear regime, the prediction of acoustic growth rates and subsequently the stability of the system is possible. A transfer matrix approach is used to solve for acoustic perturbations of pressure and velocity, stability growth rate, and frequency shift without and with porous media. The Galerkin approximation is used to approximate the stability growth rate and frequency shift, and it is compared to the numerical solution of the governing equations. Porous media is modeled using the following properties: porosity, flow resistivity, effective bulk modulus, and structure factor. The properties of porous media are systematically varied to determine the impact on the eigenfrequencies and stability growth rates. Porous media is shown to increase the stability domain for a range of time delays (Tau) compared to similar cases without porous media.
TOPICS: Porous materials, Stability, Acoustics, Transfer functions, Sound pressure, Combustion systems, Damping, Delays, Ducts, Electrical resistivity, Flames, Galerkin method, Porosity, Bulk modulus, Flow (Dynamics), Heat, Oscillations, Pressure
research-article  
Thomas Hagemann and Hubert Schwarze
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041026
Flooded lubrication of tilting-pad journal bearings provides safe and robust operation for many applications due to a completely filled gap at the leading edge of each pad. While flooded conditions can be ensured by restrictive seals on the lateral bearing ends for any conventional bearing design, direct lubrication by leading edge grooves (LEG) placed on the pads represents an alternative to produce completely filled gaps at the entrance to the convergent lubricant film. Moreover, this design is flexible to apply different axial sealing baffles in order to influence the thermal equilibrium within the entire bearing. A theoretical model is presented that describes the specific influences of LEG design on the operating characteristics. First, in opposite to conventional tilting-pad journal bearing designs the LEG is a self-contained lube oil pocket which is generally connected to an outer annular oil supply channel. Consequently, each leading edge groove can feature a specific speed and load dependent effective pocket pressure and flow rate. As a consequence of this and the fact that the LEG is part of the pad, it directly influences its tilting angle. Secondly, the thermal inlet mixing model must consider the specific flow conditions depending on the main flow direction within the film as well as the one between outer annular channel and pocket. The novel LEG model is integrated into a comprehensive bearing code and validated with test data from high performance journal bearing test rig for a four tilting-pad bearing in load between pivot orientation.
TOPICS: Experimental analysis, Journal bearings, Bearings, Flow (Dynamics), Lubrication, Design, Stress, Thermal equilibrium, Bearing design, Lubricants, Sealing (Process), Pressure
research-article  
Thomas Hagemann and Hubert Schwarze
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041026
Flooded lubrication of tilting-pad journal bearings provides safe and robust operation for many applications due to a completely filled gap at the leading edge of each pad. While flooded conditions can be ensured by restrictive seals on the lateral bearing ends for any conventional bearing design, direct lubrication by leading edge grooves (LEG) placed on the pads represents an alternative to produce completely filled gaps at the entrance to the convergent lubricant film. Moreover, this design is flexible to apply different axial sealing baffles in order to influence the thermal equilibrium within the entire bearing. A theoretical model is presented that describes the specific influences of LEG design on the operating characteristics. First, in opposite to conventional tilting-pad journal bearing designs the LEG is a self-contained lube oil pocket which is generally connected to an outer annular oil supply channel. Consequently, each leading edge groove can feature a specific speed and load dependent effective pocket pressure and flow rate. As a consequence of this and the fact that the LEG is part of the pad, it directly influences its tilting angle. Secondly, the thermal inlet mixing model must consider the specific flow conditions depending on the main flow direction within the film as well as the one between outer annular channel and pocket. The novel LEG model is integrated into a comprehensive bearing code and validated with test data from high performance journal bearing test rig for a four tilting-pad bearing in load between pivot orientation.
TOPICS: Experimental analysis, Journal bearings, Bearings, Flow (Dynamics), Lubrication, Design, Stress, Thermal equilibrium, Bearing design, Lubricants, Sealing (Process), Pressure
research-article  
Zihan Shen, Benjamin Chouvion, Fabrice Thouverez, Aline Beley and Jean-Daniel Beley
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041024
In this paper, the Co-Rotational (C-R) finite element method derived from a rotating reference frame is proposed to investigate the nonlinear vibration of rotating 2D beams with large displacement. This method has been widely applied for static analysis with very large displacement. However, at present, the application of the C-R method in the non-linear dynamic analysis is relatively limited, especially in rotating machinery simulations. The consideration of C-R method provides us with the possibility to treat geometrical nonlinearity directly with pre-extracted rigid body motion displacements. Moreover, it re-activates the existing linear finite element library, as the pure deformational displacements are also extracted. In this work, the Euler-Bernoulli beam hypotheses are used but the extension to other beam theory should not be an issue. The accuracy of the C-R formulation is examined by a convergence theoretical study by comparing the approximated strains in local C-R frames with exact ones derived in Total Lagrangian formulations. In our proposed C-R formulation, starting from the consistent expression of kinematic energy, the governing equations for nonlinear vibration are obtained by using Lagrange's equations, in which the constant angular velocity is taken into consideration. By this way, the geometrical nonlinearity of large displacement is perfectly dealt with. To enhance the numerical simulations, the mass, the Coriolis, and the tangent stiffness matrices are derived analytically. The proposed formulations are used in modal and temporal simulations comparing with results from Total-Lagrangian formulations.
TOPICS: Nonlinear vibration, Displacement, Simulation, Engineering simulation, Finite element analysis, Finite element methods, Dynamic analysis, Kinematics, Machinery, Computer simulation, Stiffness, Euler-Bernoulli beam theory
research-article  
Zihan Shen, Benjamin Chouvion, Fabrice Thouverez, Aline Beley and Jean-Daniel Beley
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041024
In this paper, the Co-Rotational (C-R) finite element method derived from a rotating reference frame is proposed to investigate the nonlinear vibration of rotating 2D beams with large displacement. This method has been widely applied for static analysis with very large displacement. However, at present, the application of the C-R method in the non-linear dynamic analysis is relatively limited, especially in rotating machinery simulations. The consideration of C-R method provides us with the possibility to treat geometrical nonlinearity directly with pre-extracted rigid body motion displacements. Moreover, it re-activates the existing linear finite element library, as the pure deformational displacements are also extracted. In this work, the Euler-Bernoulli beam hypotheses are used but the extension to other beam theory should not be an issue. The accuracy of the C-R formulation is examined by a convergence theoretical study by comparing the approximated strains in local C-R frames with exact ones derived in Total Lagrangian formulations. In our proposed C-R formulation, starting from the consistent expression of kinematic energy, the governing equations for nonlinear vibration are obtained by using Lagrange's equations, in which the constant angular velocity is taken into consideration. By this way, the geometrical nonlinearity of large displacement is perfectly dealt with. To enhance the numerical simulations, the mass, the Coriolis, and the tangent stiffness matrices are derived analytically. The proposed formulations are used in modal and temporal simulations comparing with results from Total-Lagrangian formulations.
research-article  
Klaus Brun, Sarah Simons, Kelsi Katcher, Ryan Cater, Brandon Ridens and Rainer Kurz
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041023
Gas property prediction is necessary for proper design of compressors. Equations of state are utilized to predict the thermo-physical gas properties needed for such calculations. These are semi-empirical models that allow the calculation of thermodynamic properties such as density, enthalpy, and speed of sound of gas mixtures for known pressures and temperature. Currently, there is limited or no data publically available to verify the results of these equation of state calculations for the range of pressures, temperatures and gas compositions relevant to many oil & gas applications. Especially for isentropic enthalpy head (i.e., the enthalpy rise along constant entropy lines), which is a critical parameter required to accurately design and performance test compressors, limited public domain data is available for equation of state validation. In this paper a method and test apparatus is described to measure compression enthalpy rise directly. In this apparatus a test gas is compressed using a fast acting piston inside an adiabatic autoclave. Test results are then corrected using calibration efficiencies from a known reference gas compression process at a similar Reynolds number. The paper describes the test apparatus, calibration, measurement methodology, and test results for one complex hydrocarbon gas composition at elevated temperatures and pressures. An uncertainty analysis of the new measurement method is also presented and results are compared to several equations of state. The results show that commonly used equations of state significantly under-predicted the compression enthalpy rise for the test gas case by more than 6%.
TOPICS: Compression, Enthalpy, Equations of state, Temperature, Compressors, Design, Calibration, Density, Speed of sound, Reynolds number, Entropy, Pistons, Testing performance, Uncertainty analysis
research-article  
Klaus Brun, Sarah Simons, Kelsi Katcher, Ryan Cater, Brandon Ridens and Rainer Kurz
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041023
Gas property prediction is necessary for proper design of compressors. Equations of state are utilized to predict the thermo-physical gas properties needed for such calculations. These are semi-empirical models that allow the calculation of thermodynamic properties such as density, enthalpy, and speed of sound of gas mixtures for known pressures and temperature. Currently, there is limited or no data publically available to verify the results of these equation of state calculations for the range of pressures, temperatures and gas compositions relevant to many oil & gas applications. Especially for isentropic enthalpy head (i.e., the enthalpy rise along constant entropy lines), which is a critical parameter required to accurately design and performance test compressors, limited public domain data is available for equation of state validation. In this paper a method and test apparatus is described to measure compression enthalpy rise directly. In this apparatus a test gas is compressed using a fast acting piston inside an adiabatic autoclave. Test results are then corrected using calibration efficiencies from a known reference gas compression process at a similar Reynolds number. The paper describes the test apparatus, calibration, measurement methodology, and test results for one complex hydrocarbon gas composition at elevated temperatures and pressures. An uncertainty analysis of the new measurement method is also presented and results are compared to several equations of state. The results show that commonly used equations of state significantly under-predicted the compression enthalpy rise for the test gas case by more than 6%.
research-article  
Jindrich Liska, Jan Jakl and Sven Kunkel
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041006
Online evaluation of possible failures of a turbine is a key factor for a successful long-term turbine operation. Fluctuations of generator air-gap torque, caused for example by non-stationary conditions of electrical power grid, influence shaft torsional vibrations as well as rotating blades vibrations. Symptoms of shaft torsional vibrations are not measurable by normally used relative shaft vibrations sensors, so special measurement must be used. The direct consequence of shaft torsional vibrations is local acceleration or deceleration of shaft circumference when it is measured by a stationary sensor. This article deals with a measurement method using an optical probe measuring the passage of black and white stripes of a zebra tape which is stuck on the rotor. The shaft torsional vibrations manifest themselves as a phase modulation of the optical probe output signal, so the sampling rate influence the achievable resolution of the calculated shaft vibrations. The presented method for the calculation of the shaft torsional vibrations is based on the evaluation of shaft instantaneous angular velocity. The advantage of this method is a direct compensation of possible non-regular geometry of the zebra tape. The analysis of shaft torsional vibrations evaluation using this method is supplemented by two case studies from the authors' current work.
TOPICS: Vibration, Sensors, Probes, Turbines, Signals, Rotating blades, Torque, Electricity (Physics), Fluctuations (Physics), Resolution (Optics), Rotors, Failure, Generators, Geometry
research-article  
Georg A. Mensah, Luca Magri, Alessandro Orchini and Jonas P. Moeck
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041007
Gas-turbine combustion chambers typically consist of nominally identical sectors arranged in a rotationally symmetric pattern. However, in practice the geometry is not perfectly symmetric. This may be due to design decisions, such as placing dampers in an azimuthally non-uniform fashion, or to uncertainties in the design parameters, which break the rotational symmetry of the combustion chamber. The question is whether these deviations from symmetry have impact to the thermoacoustic-stability calculation. The paper addresses this question by proposing a fast adjoint-based perturbation method. This method can be integrated into numerical frameworks that are industrial standard such as lumped-network models, Helmholtz- and linearized Euler-equations. The thermoacoustic stability of asymmetric combustion chambers is investigated by perturbing rotationally symmetric combustor models. The approach proposed in this paper is applied to a realistic three-dimensional combustion chamber model with an experimentally measured flame transfer function, which is solved with a Helmholtz solver. Results for modes of zeroth, first, and second azimuthal mode order are presented and compared to exact solutions of the problem. A focus of the discussion is set on the loss of mode-degeneracy due to symmetry breaking and the capability of the perturbation theory to accurately predict it. In particular, an "inclination rule'' that explains the behavior of degenerate eigenvalues at first order is proven.
TOPICS: Combustion chambers, Stability, Design, Gas turbines, Eigenvalues, Flames, Geometry, Perturbation theory, Uncertainty, Transfer functions, Dampers
research-article  
Michael Wilkinson, Sybrand J. van der Spuy and Theodor W. von Backström
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041010
An axial flow fan developed in previous study is tested in order to characterise its performance. The M-fan, a 7.3152 m diameter rotor only axial flow fan was designed to perform well under the challenging operating conditions encountered in air-cooled heat exchangers. Preliminary CFD results indicate that the fan meets the specified performance targets. Several fan configurations are tested experimentally in order to ascertain the effect of tip clearance, blade angle and hub configuration on fan performance. A scaled 1.542 m diameter model of the M-fan is tested on an ISO 5801 type A fan test facility. A RANS CFD model representing the M-fan in the test facility is also developed in order to provide additional insight into the flow field in the vicinity of the fan blades. Experimental data indicates that the M-fan does not meet the pressure requirement set out in the initial study, at the design blade setting angle. Increasing the blade angle is shown to improve the total-to-static pressure rise and efficiency obtained at the operating point. The M-fan is also shown to be highly sensitive to increasing tip gap effects, however tip losses are also shown to be overestimated by the CFD simulations. Results indicate that the M-fan is suited to its intended application, however its opperating configuration should be adjusted. Hub configuration is also shown to have an influence on fan performance, potentially improving performance at low flow rates.
TOPICS: Heat exchangers, Axial flow, Testing performance, Blades, Computational fluid dynamics, Pressure, Flow (Dynamics), Test facilities, Reynolds-averaged Navier–Stokes equations, Simulation, Clearances (Engineering), Design, Engineering simulation, Rotors
research-article  
Alexandre Gontcharov, Yuan Tian, Paul Lowden and Mathieu Brochu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041009
The microstructure and mechanical properties of materials produced by Wide Gap Brazing (WGB) and Laser Beam (LBW) cladding with different blends of Mar M247 and Amdry DF-3 brazing powders were studied. It was shown that LBW Mar M247 based materials comprised of 0.6 to 1 wt. % B were weldable. The weld properties were superior to WGB deposits with the same bulk chemical composition, due to the formation of a dendritic structure typical for welded joints, and the precipitation of cuboidal borides of Cr, Mo, and Win the ductile Ni-Cr based matrix. Both materials were found to have useful properties for 3D additive manufacturing (AM) and repair components manufactured from high gamma prime precipitation hardened superalloys. GT2018-75870
TOPICS: Laser beams, Mechanical properties, Brazing, Cladding systems (Building), Precipitation, Additive manufacturing, Precipitation hardening, Welded joints, Maintenance, Superalloys
research-article  
Robby Weber and Arnold Kühhorn
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040999
Usually, in the field of turbomachinery, identical blades are assumed to lower the required computational resources. However, mistuning is unavoidable, since small deviations due to the manufacturing process will lead to slightly different blade behavior. Potential effects such as mode localization and amplification can be treated statistically and have been thoroughly studied in the past. Since then, several reduced order models (ROMs) have been invented in order to calculate the maximum vibration amplitude of a fleet of mistuned blisks. Nowadays, it is common knowledge that the level of manufacturing imperfection (referred as level of mistuning) significantly influence mode localization as well as vibration amplification effects. Optical measurements of the geometric deviations of manufactured blades and converting to a high-fidelity finite element model make huge progress. However, to the knowledge of the authors, there is no reliable method, that derives a characteristic quantity from the geometric mistuning, that fits into the mentioned statistically approaches. Therefore, experimental data is needed to quantify the level of mistuning. Several approaches, which isolate blade individual parameters, are used to identify the dynamic behavior of axial compressors and turbines. These methods can be applied to medium-speed centrifugal turbine wheels but tend to fail to evaluate high-speed compressor with splitter blades. This paper briefly presents the original approach and discusses the reasons for failure. Thereafter, a new approach is proposed. Finally, the level of mistuning and important quantities to perform a statistical evaluation of a high-speed compressor is shown.
TOPICS: Compressors, Blades, Manufacturing, Turbines, Vibration, Failure, Finite element model, Turbomachinery, Wheels, Optical measurement
research-article  
Stian Madsen and Lars E. Bakken
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041002
Optimized operation of gas turbines is discussed for a fleet of eleven GE LM2500PE engines at a Statoil North Sea offshore field in Norway. Three engines are generator drivers and eight engines are compressor drivers. Several of the compressor drive engines are running at peak load (T5.4 control), hence production rate is limited by the available power from these engines. The majority of the engines discussed run continuously without redundancy, hence gas turbine uptime is critical for the field's production and economy. The performance and operational experience with online water wash at high water-to-air ratio, as well as successful operation at longer maintenance intervals and higher average engine performance are described. Water-to-air ratio is significantly increased compared to the OEM limit (OEM limit is 17 l/min which yields approx. 0.5% water-to-air ratio). Today the engines are operated at a water rate of 50 l/min (3 times the OEM limit) which yields a 1.4% water-to-air ratio. Such a high water-to-air ratio has been proven to be the key parameter for obtaining good online water wash effectiveness. Possible downsides of high water-to-air ratio have been thoroughly studied.
TOPICS: Ocean engineering, Gas turbines, Water, Engines, Compressors, Generators, Peak load, Redundancy (Engineering), Economics , North Sea, Maintenance
research-article  
Renaud Gaudron, Marco Gatti, CLEMENT MIRAT and Thierry Schuller
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041000
The frequency response of a confined premixed swirled flame is explored experimentally through the use of describing functions that depend on both the forcing frequency and forcing level. In these experiments, the flame is forced by a loudspeaker connected to the bottom of the burner in the fresh gas region or by a set of loudspeakers connected to the combustion chamber exhaust tube in the burnt gas region. The experimental setup is equipped with a hot-wire probe and a microphone, both of which located in front of each other below the swirler. The forcing level is varied between 0.10 and 0.72 RMS. An additional microphone is placed on a water-cooled waveguide connected to the combustion chamber backplate. A photomultiplier equipped with an OH* filter is used to measure the heat release rate fluctuations. The describing functions between the photomultiplier signal and the different pressure and velocity reference signals are then analyzed in the case of upstream and downstream forcing. The describing function measured for a given reference signal is shown to vary depending on the type of forcing. The impedance of the injector at the hot-wire location is also measured using the hot-wire and microphone signals for both upstream and downstream forcing. For all describing functions investigated, it is found that their phase lags do not depend on the forcing level whereas their gains strongly depend on the forcing level for certain frequency ranges... (See end of abstract in the article)
TOPICS: Combustion chambers, Flames, Signals, Microphones, Wire, Loudspeakers, Water, Probes, Waveguides, Frequency response, Fluctuations (Physics), Pressure, Heat, Ejectors, Exhaust systems, Filters
research-article  
Cody Allen, Chad Holcomb and Mauricio C. de Oliviera
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041004
Many of the components on a gas turbine are subject to fouling and degradation over time due to debris buildup. For example, axial compressors are susceptible to degradation as a result of debris buildup on compressor blades. Similarly, air cooled lube oil heat exchangers incur degradation as a result of debris buildup in the cooling air passageways. In this paper, we develop a method for estimating the degradation rate of a given gas turbine component that experiences recoverable degradation due to normal operation over time. We then establish an economic maintenance scheduling model which utilizes the derived rate and user input economic factors to provide a locally optimal maintenance schedule with minimized operator costs. The rate estimation method makes use of statistical methods combined with historical data to give an algorithm with which a performance loss rate can be extracted from noisy data measurements. The economic maintenance schedule is then derived by minimizing the cost model in user specified intervals and the final schedule results as a combination of the locally optimized schedules. The goal of the combination of algorithms is to maximize component output and efficiency, while minimizing maintenance costs. The rate estimation method is validated by simulation where the underlying noisy data measurements come from a known probability distribution. Then, an example schedule optimization is provided to validate the economic optimization model and show the efficacy of the combined methods.
TOPICS: Maintenance, Compressors, Algorithms, Gas turbines, Optimization, Blades, Statistical distributions, Cooling, Heat exchangers, Simulation

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In