High-Frequency Thermoacoustic Modulation Mechanisms in Swirl-Stabilized Gas Turbine Combustors—Part II: Modeling and Analysis

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Tobias Hummel ◽  
Frederik Berger ◽  
Michael Hertweck ◽  
Bruno Schuermans ◽  
Thomas Sattelmayer
Keyword(s):  
Gas Turbine ◽  
High Frequency ◽  
Transfer Functions ◽  
Temperature Fields ◽  
Linear Feedback ◽  
Modeling And Analysis ◽  
Gas Turbine Combustors ◽  
Relative Contribution ◽  
Driving Mechanisms ◽  
Acoustic Instabilities

This paper deals with high-frequency (HF) thermoacoustic instabilities in swirl-stabilized gas turbine combustors. Driving mechanisms associated with periodic flame displacement and flame shape deformations are theoretically discussed, and corresponding flame transfer functions (FTF) are derived from first principles. These linear feedback models are then evaluated by means of a lab-scale swirl-stabilized combustor in combination with part one of this joint publication. For this purpose, the models are used to thermoacoustically characterize a complete set of operation points of this combustor facility. Specifically, growth rates of the first transversal modes are computed, and compared against experimentally obtained pressure amplitudes as an indicator for thermoacoustic stability. The characterization is based on a hybrid analysis approach relying on a frequency domain formulation of acoustic conservation equations, in which nonuniform temperature fields and distributed thermoacoustic source terms/flame transfer functions can be straightforwardly considered. The relative contribution of flame displacement and deformation driving mechanisms–i.e., their significance with respect to the total driving–is identified. Furthermore, promoting/inhibiting conditions for the occurrence of high frequency, transversal acoustic instabilities within swirl-stabilized gas turbine combustors are revealed.

High-Frequency Thermoacoustic Modulation Mechanisms in Swirl-Stabilized Gas Turbine Combustors: Part Two — Modeling and Analysis

2016 ◽  
Author(s):  
Tobias Hummel ◽  
Frederik Berger ◽  
Michael Hertweck ◽  
Bruno Schuermans ◽  
Thomas Sattelmayer
Keyword(s):  
Gas Turbine ◽  
High Frequency ◽  
Transfer Functions ◽  
Temperature Fields ◽  
Linear Feedback ◽  
Modeling And Analysis ◽  
Gas Turbine Combustors ◽  
Relative Contribution ◽  
Driving Mechanisms ◽  
Acoustic Instabilities

This paper deals with high-frequency thermoacoustic instabilities in swirl-stabilized gas turbine combustors. Driving mechanisms associated with periodic flame displacement and flame shape deformations are theoretically discussed, and corresponding flame transfer functions are derived from first principles. These linear feedback models are then evaluated by means of a lab-scale swirl-stabilized combustor in combination with part one of this joint publication. For this purpose, the models are used to thermoacoustically characterize a complete set of operation points of a this combustor facility. Specifically, growth rates of the first transversal modes are computed, and compared against experimentally obtained pressure amplitudes as an indicator for thermoacoustic stability. The characterization is based on a hybrid analysis approach relying on a frequency domain formulation of acoustic conservation equations, in which non-uniform temperature fields and distributed thermoacoustic source terms / flame transfer functions can be straightforwardly considered. The relative contribution of flame displacement and deformation driving mechanisms — i.e. their significance with respect to the total driving — is identified. Furthermore, promoting/ inhibiting conditions for the occurrence of high frequency, transversal acoustic instabilities within swirl-stabilized gas turbine combustors are revealed.

High Frequency Thermoacoustic Modulation Mechanisms in Swirl-Stabilized Gas Turbine Combustors: Part One — Experimental Investigation of Local Flame Response

2016 ◽  
Author(s):  
Frederik M. Berger ◽  
Tobias Hummel ◽  
Michael Hertweck ◽  
Jan Kaufmann ◽  
Bruno Schuermans ◽  
...  
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
High Frequency ◽  
Transfer Functions ◽  
Temporal Dynamics ◽  
Dynamic Pressure ◽  
Radon Transforms ◽  
Gas Turbine Combustors ◽  
High Modulation ◽  
The Impact

This paper presents the experimental approach for determination and validation of non-compact flame transfer functions of high frequency, transverse combustion instabilities observed in a generic lean premixed gas turbine combustor. The established non-compact transfer functions describe the interaction of the flame’s heat release with the acoustics locally, which is necessary due to the respective length scales being of the same order of magnitude. Spatio-temporal dynamics of the flame are measured by imaging the OH* chemiluminescence signal, phase-locked to the dynamic pressure at the combustor’s front plate. Radon transforms provide a local insight into the flame’s modulated reaction zone. Applied to different burner configurations, the impact of the unsteady heat release distribution on the thermoacoustic driving potential, as well as distinct flame regions that exhibit high modulation intensity are revealed. Utilizing these spatially distributed transfer functions within thermoacoustic analysis tools (addressed in this joint publication’s part two) allows then to predict transverse linear stability of gas turbine combustors.

High-Frequency Thermoacoustic Modulation Mechanisms in Swirl-Stabilized Gas Turbine Combustors—Part I: Experimental Investigation of Local Flame Response

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Frederik M. Berger ◽  
Tobias Hummel ◽  
Michael Hertweck ◽  
Jan Kaufmann ◽  
Bruno Schuermans ◽  
...  
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
High Frequency ◽  
Transfer Functions ◽  
Dynamic Pressure ◽  
Radon Transforms ◽  
Gas Turbine Combustors ◽  
High Modulation ◽  
Order Of Magnitude ◽  
The Impact

This paper presents the experimental approach for determination and validation of noncompact flame transfer functions of high-frequency, transverse combustion instabilities observed in a generic lean premixed gas turbine combustor. The established noncompact transfer functions describe the interaction of the flame's heat release with the acoustics locally, which is necessary due to the respective length scales being of the same order of magnitude. Spatiotemporal dynamics of the flame are measured by imaging the OH⋆ chemiluminescence signal, phase-locked to the dynamic pressure at the combustor's front plate. Radon transforms provide a local insight into the flame's modulated reaction zone. Applied to different burner configurations, the impact of the unsteady heat release distribution on the thermoacoustic driving potential, as well as distinct flame regions that exhibit high modulation intensity, is revealed. Utilizing these spatially distributed transfer functions within thermoacoustic analysis tools (addressed in this joint publication's Part II) allows then to predict transverse linear stability of gas turbine combustors.

scholarly journals A Three-Dimensional Algebraic Grid Generation Scheme for Gas Turbine Combustors With Inclined Slots

1992 ◽  
Author(s):  
S. L. Yang ◽  
M. C. Cline ◽  
R. Chen ◽  
Y.-L. Chang
Keyword(s):  
Gas Turbine ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Interpolation Method ◽  
Cross Flow ◽  
Grid Generation ◽  
Temperature Fields ◽  
Computational Grids ◽  
Gas Turbine Combustors ◽  
Ring Shape

Abstract A 3D algebraic grid generation scheme is presented for generating the grid points inside gas turbine combustors with inclined slots. The scheme is based on the 2D transfinite interpolation method. Since the scheme is a 2D approach, it is very efficient and can be easily extended to gas turbine combustors with either dilution hole or slot configurations. To demonstrate the feasibility and the usefulness of the technique, a numerical study of the quick-quench/lean-combustion (QQ/LC) zones of a staged turbine combustor is given. Preliminary results illustrate some of the major features of the flow and temperature fields in the QQ/LC zones. Formation of co- and counter-rotating bulk flow and sandwiched-ring-shape temperature fields, typical of the confined slanted jet-in-cross flow, can be observed clearly. Numerical solutions show the method to be an efficient and reliable tool for generating computational grids for analyzing gas turbine combustors with slanted slots.

A Method for Estimating the Onset of Acoustic Instabilities in Premixed Gas-Turbine Combustors

2007 ◽  
Author(s):  
Z. M. Ibrahim ◽  
F. A. Williams ◽  
S. G. Buckley ◽  
C. Z. Twardochleb
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Gas Turbine ◽  
Classical Method ◽  
Stability Index ◽  
Operating Conditions ◽  
Linear Amplification ◽  
Gas Turbine Combustors ◽  
Acoustic Instabilities ◽  
Oscillatory Combustion

For given acoustic frequencies of premixed gas-turbine combustors, a classical method not currently in use is explored for assessing whether acoustically driven oscillatory combustion will occur. The method involves cataloging linear amplification and attenuation mechanisms and estimating magnitudes of their rates. Linear approximations to nonlinear mechanisms are included in an effort to obtain a reasonably complete description. A stability index is defined such that oscillation is predicted to occur when the value of the index exceeds unity. The method is tested on the basis of new experiments and experimental data available in the literature. Moderate success is achieved in rationalizing these experimental results. The objective of the method is to enable quick and inexpensive decisions to be made for a wide variety of potential design configurations and operating conditions, without the complexity of computational fluid dynamics. The approach therefore may complement other approaches already in use.

An Acoustic-Energy Method for Estimating the Onset of Acoustic Instabilities in Premixed Gas-Turbine Combustors

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Z. M. Ibrahim ◽  
F. A. Williams ◽  
S. G. Buckley ◽  
C. Z. Twardochleb
Keyword(s):  
Experimental Data ◽  
Gas Turbine ◽  
Classical Method ◽  
Stability Index ◽  
Operating Conditions ◽  
Acoustic Energy ◽  
Linear Amplification ◽  
Gas Turbine Combustors ◽  
Acoustic Instabilities ◽  
Oscillatory Combustion

For given acoustic frequencies of premixed gas-turbine combustors, a classical method not currently in use is explored for assessing whether acoustically driven oscillatory combustion will occur. The method involves cataloging linear amplification and attenuation mechanisms and estimating magnitudes of their rates. Linear approximations to nonlinear mechanisms are included in an effort to obtain a reasonably complete description. A stability index is defined such that oscillation is predicted to occur when the value of the index exceeds unity. The method is tested on the basis of new experiments and experimental data available in literature. Moderate success is achieved in rationalizing these experimental results. The objective of the method is to enable quick and inexpensive decisions to be made for a wide variety of potential design configurations and operating conditions, without the complexity of computational fluid dynamics. The approach therefore may complement other approaches already in use.

Linearized Euler Equations for the Prediction of Linear High-Frequency Stability in Gas Turbine Combustors

2016 ◽  
Author(s):  
Moritz Schulze ◽  
Tobias Hummel ◽  
Noah Klarmann ◽  
Frederik Berger ◽  
Bruno Schuermans ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Gas Turbine ◽  
Linear Stability ◽  
Euler Equations ◽  
Linear Stability Analysis ◽  
High Frequency ◽  
Mean Flow ◽  
Linearized Euler Equations ◽  
Gas Turbine Combustors ◽  
Transversal Mode

A novel methodology for linear stability analysis of high-frequency thermoacoustic oscillations in gas turbine combustors is presented. The methodology is based on the linearized Euler equations, which yield a high-fidelity description of acoustic wave propagation and damping in complex, non-uniform, reactive mean flow environments, such as encountered in gas turbine combustion chambers. Specifically, this work introduces three novelties to the community: (1) Linear stability analysis on the basis of linearized Euler equations. (2) Explicit consideration of three-dimensional, acoustic oscillations at screech level frequencies, particularly the first transversal mode. (3) Handling of non-compact flame coupling with LEE, that is, the spatially varying coupling dynamics between perturbation and unsteady flame response due to small acoustic wavelengths. Two different configurations of an experimental model combustor in terms of thermal power and mass flow rates are subject of the analysis. Linear flame driving is modeled by prescribing the unsteady heat release source term of the linearized Euler equations by local flame transfer functions, which are retrieved from first principles. The required steady state flow field is numerically obtained via CFD, which is based on an extended Flamelet-Generated Manifold combustion model, taking into account heat transfer to the environment. The model is therefore highly suitable for such types of combustors. The configurations are simulated, and thermoacoustically characterized in terms of eigenfrequencies and growth rates associated with the first transversal mode. The findings are validated against experimentally observed thermoacoustic stability characteristics. On the basis of the results, new insights into the acoustic field are discussed.

Linearized Euler Equations for the Prediction of Linear High-Frequency Stability in Gas Turbine Combustors

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Moritz Schulze ◽  
Tobias Hummel ◽  
Noah Klarmann ◽  
Frederik Berger ◽  
Bruno Schuermans ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Gas Turbine ◽  
Linear Stability ◽  
Euler Equations ◽  
Linear Stability Analysis ◽  
High Frequency ◽  
Mean Flow ◽  
Linearized Euler Equations ◽  
Gas Turbine Combustors ◽  
Transversal Mode

A novel methodology for linear stability analysis of high-frequency thermoacoustic oscillations in gas turbine combustors is presented. The methodology is based on the linearized Euler equations (LEEs), which yield a high-fidelity description of acoustic wave propagation and damping in complex, nonuniform, reactive mean flow environments, such as encountered in gas turbine combustion chambers. Specifically, this work introduces three novelties to the community: (1) linear stability analysis on the basis of linearized Euler equations. (2) Explicit consideration of three-dimensional, acoustic oscillations at screech level frequencies, particularly the first-transversal mode. (3) Handling of noncompact flame coupling with LEE, that is, the spatially varying coupling dynamics between perturbation and unsteady flame response due to small acoustic wavelengths. Two different configurations of an experimental model combustor in terms of thermal power and mass flow rates are subject of the analysis. Linear flame driving is modeled by prescribing the unsteady heat release source term of the linearized Euler equations by local flame transfer functions, which are retrieved from first principles. The required steady-state flow field is numerically obtained via computational fluid dynamics (CFD), which is based on an extended flamelet-generated manifold (FGM) combustion model, taking into account heat transfer to the environment. The model is therefore highly suitable for such types of combustors. The configurations are simulated, and thermoacoustically characterized in terms of eigenfrequencies and growth rates associated with the first-transversal mode. The findings are validated against experimentally observed thermoacoustic stability characteristics. On the basis of the results, new insights into the acoustic field are discussed.

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