High-Frequency Instability Driving Potential of Premixed Jet Flames in a Tubular Combustor due to Dynamic Compression and Deflection

2020 ◽  
Author(s):  
Payam Mohammadzadeh Keleshtery ◽  
Gerrit Heilmann ◽  
Christoph Hirsch ◽  
Lukasz Panek ◽  
Michael Huth ◽  
...  
Keyword(s):  
Heat Release ◽  
Growth Rates ◽  
High Frequency ◽  
Dynamic Compression ◽  
Thermal Power ◽  
Design Parameters ◽  
Flame Dynamics ◽  
Dynamics Models ◽  
The Impact ◽  
Driving Potential

Abstract Constructive interference of acoustic oscillations and combustion heat release can result in high-frequency thermoacoustic instabilities in gas turbine combustion chambers with strong pressure pulsations. They may cause component wear and limit the safe operating range of the engine. During the development of stable combustors the influence of design variables on the driving mechanisms of these instabilities is of particular interest. This paper studies the influence of design parameters on the linear growth rates of high-frequency thermoacoustic transverse modes in a tubular combustor of hexagonal cross-section equipped with 12 turbulent premixed jet burners. Two flame dynamics models are used, i. e. the dynamic compression and the deflection mechanisms, which have in the past been validated for turbulent swirl burners. To demonstrate the applicability as well as the shortfalls of these flame dynamics models the impact of different geometrical and flow parameters on the driving potential of high-frequency thermoacoustic modes are considered. A parameter variation study of thermal power, air excess ratio, diameter of the combustor and the radial position of jet burners was performed. The first transversal eigenmodes and eigenfrequencies were computed by solving the inhomogeneous Helmholtz equation with the flame driving source terms in the frequency domain using the finite element method. The required mean fields of temperature and heat release rate were obtained using a generic flame distribution scaled with respect to the experimental OH* chemiluminescence measurements. The resulting growth rates give a measure for the thermoacoustic driving potential.

Pulsation-Amplitude-Dependent Flame Dynamics of High-Frequency Thermoacoustic Oscillations in Lean-Premixed Gas Turbine Combustors

2017 ◽  
Author(s):  
Frederik M. Berger ◽  
Tobias Hummel ◽  
Bruno Schuermans ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Growth Rates ◽  
High Frequency ◽  
Individual Growth ◽  
Mean Flow ◽  
Flame Dynamics ◽  
Pulsation Amplitude ◽  
The Mean ◽  
Thermoacoustic Oscillations

This paper presents the experimental investigation of pulsation-amplitude-dependent flame dynamics associated with transverse thermoacoustic oscillations at screech level frequencies in a generic gas turbine combustor. Specifically, the flame behavior at different levels of pulsation amplitudes is assessed and interpreted. Spatial dynamics of the flame are measured by imaging the OH* chemiluminescence signal synchronously to the dynamic pressure at the combustor’s face plate. First, linear thermoacoustic stability states, modal dynamics, as well as flame-acoustic phase relations are evaluated. It is found that the unstable acoustic modes converge into a predominantly rotating character in the direction of the mean flow swirl. Furthermore, the flame modulation is observed to be in phase with the acoustic pressure at all levels of the oscillation amplitude. Second, distributed flame dynamics are investigated by means of visualizing the mean and oscillating heat release distribution at different pulsation amplitudes. The observed flame dynamics are then compared against numerical evaluations of the respective amplitude-dependent thermoacoustic growth rates, which are computed using analytical models in the fashion of a non-compact flame-describing function. While results show a nonlinear contribution for the individual growth rates, the superposition of flame deformation and displacements balances out to a constant flame driving. This latter observation contradicts the state-of-the-art perception of root-causes for limit-cycle oscillations in thermoacoustic gas turbine systems, for which the heat release saturates with increasing amplitudes. Consequently, the systematic observations and analysis of amplitude-dependent flame modulation shows alternative paths to the explanation of mechanisms that might cause thermoacoustic saturation in high frequency systems.

Pulsation-Amplitude-Dependent Flame Dynamics of High-Frequency Thermoacoustic Oscillations in Lean-Premixed Gas Turbine Combustors

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Frederik M. Berger ◽  
Tobias Hummel ◽  
Bruno Schuermans ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Growth Rates ◽  
High Frequency ◽  
Individual Growth ◽  
Mean Flow ◽  
Flame Dynamics ◽  
Pulsation Amplitude ◽  
The Mean ◽  
Thermoacoustic Oscillations

This paper presents the experimental investigation of pulsation-amplitude-dependent flame dynamics associated with transverse thermoacoustic oscillations at screech level frequencies in a generic gas turbine combustor. Specifically, the flame behavior at different levels of pulsation amplitudes is assessed and interpreted. Spatial dynamics of the flame are measured by imaging the OH⋆ chemiluminescence (CL) signal synchronously to the dynamic pressure at the combustor's face plate. First, linear thermoacoustic stability states, modal dynamics, and flame-acoustic phase relations are evaluated. It is found that the unstable acoustic modes converge into a predominantly rotating character in the direction of the mean flow swirl. Furthermore, the flame modulation is observed to be in phase with the acoustic pressure at all levels of the oscillation amplitude. Second, distributed flame dynamics are investigated by means of visualizing the mean and oscillating heat release distribution at different pulsation amplitudes. The observed flame dynamics are then compared against numerical evaluations of the respective amplitude-dependent thermoacoustic growth rates, which are computed using analytical models in the fashion of a noncompact flame-describing function. While results show a nonlinear contribution for the individual growth rates, the superposition of flame deformation and displacement balances out to a constant flame driving. This latter observation contradicts the state-of-the-art perception of root-causes for limit-cycle oscillations in thermoacoustic gas turbine systems, for which the heat release saturates with increasing amplitudes. Consequently, the systematic observations and analysis of amplitude-dependent flame modulation shows alternative paths to the explanation of mechanisms that might cause thermoacoustic saturation in high frequency systems.

Low-Order Modeling of Nonlinear High-Frequency Transversal Thermoacoustic Oscillations in Gas Turbine Combustors

2016 ◽  
Author(s):  
Tobias Hummel ◽  
Klaus Hammer ◽  
Pedro Romero ◽  
Bruno Schuermans ◽  
Thomas Sattelmayer
Keyword(s):  
Dynamical System ◽  
Gas Turbine ◽  
High Frequency ◽  
Linear Part ◽  
Combustion Noise ◽  
Dynamical System Theory ◽  
Flame Dynamics ◽  
The Impact ◽  
Thermoacoustic Oscillations ◽  
Low Order

This paper analyzes transversal thermoacoustic oscillations in an experimental gas turbine combustor utilizing dynamical system theory. Limit cycle acoustic motions related to the first linearly unstable transversal mode of a given 3D combustor configuration are modeled, and reconstructed by means of a low order dynamical system simulation. The source of nonlinearity is solely allocated to flame dynamics, saturating the growth of acoustic amplitudes, while the oscillation amplitudes are assumed to always remain within the linearity limit. First, a Reduced Order Model (ROM), which reproduces the combustor’s modal distribution and damping of acoustic oscillations is derived. The ROM is a low-order state-space system, which results from a projection of the Linearized Euler Equations (LEE) into their truncated eigenspace. Second, flame dynamics are modeled as a function of acoustic perturbations by means of a nonlinear transfer function. This function has a linear and a nonlinear contribution. The linear part is modeled analytically from first principles, while the nonlinear part is mathematically cast into a cubic saturation functional form. Additionally, the impact of stochastic forcing due to broadband combustion noise is included by additive white noise sources. Then, the acoustic and the flame system is interconnected, where thermoacoustic non-compactness due to the transversal modes’ high frequency is accounted for by a distributed source term framework. The resulting nonlinear thermoacoustic system is solved in frequency and time domain. Linear growth rates predict linear stability, while envelope plots and probability density diagrams of the resulting pressure traces characterize the thermoacoustic performance of the combustor from a dynamical systems theory perspective. Comparisons against experimental data are conducted, which allow the rating of the flame modes in terms of their capability to reproduce the observed combustor dynamics. Ultimately, insight into the physics of high-frequency, transversal thermoacoustic systems is created.

scholarly journals Impact of the heat release distribution on high-frequency transverse thermoacoustic driving in premixed swirl flames

2016 ◽  
Vol 9 (3) ◽  
pp. 143-154 ◽  
Author(s):  
Michael Hertweck ◽  
Frederik M Berger ◽  
Tobias Hummel ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
High Frequency ◽  
Transfer Functions ◽  
Three Dimensional ◽  
Elevated Pressure ◽  
Rayleigh Index ◽  
The Stability ◽  
Stability Limits ◽  
The Impact

Self-excited, high-frequency first transversal thermoacoustic instabilities in a cylindrical combustion chamber equipped with a premixed swirl-stabilized flame are investigated. Phase-locked image analysis of the phenomena shows the displacement of the flame and a higher burning rate in the region of elevated pressure. The impact of diffuser angle and fuel composition on the stability limits and the flame position is investigated. The Rayleigh-Index is computed for a three-dimensional domain based on analytical flame transfer functions for experimentally obtained data of OH*-chemiluminescence as measure for the spatial heat release. Two models from different sources are applied, which describe the interaction between flame and acoustic locally. The axial dependence of the amplitude of the transversal mode is computed by a numerical model, which takes the temperature distribution inside the combustion chamber into account. The comparison of the Rayleigh-Index of different operation points shows a correlation with the stability limits for some, but not for all investigated configurations.

High-Frequency Instability Driving Potential of Premixed Jet Flames in a Tubular Combustor due to Dynamic Compression and Deflection

2021 ◽  
Author(s):  
Payam Mohammadzadeh Keleshtery ◽  
Gerrit Heilmann ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer ◽  
Michael Huth ◽  
...  
Keyword(s):  
High Frequency ◽  
Dynamic Compression ◽  
Frequency Instability ◽  
Jet Flames ◽  
Driving Potential

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.

Low-Order Modeling of Nonlinear High-Frequency Transversal Thermoacoustic Oscillations in Gas Turbine Combustors

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Tobias Hummel ◽  
Klaus Hammer ◽  
Pedro Romero ◽  
Bruno Schuermans ◽  
Thomas Sattelmayer
Keyword(s):  
Dynamical System ◽  
Gas Turbine ◽  
High Frequency ◽  
Linear Part ◽  
Combustion Noise ◽  
Dynamical System Theory ◽  
Flame Dynamics ◽  
The Impact ◽  
Thermoacoustic Oscillations ◽  
Low Order

This paper analyzes transversal thermoacoustic oscillations in an experimental gas turbine combustor utilizing dynamical system theory. Limit-cycle acoustic motions related to the first linearly unstable transversal mode of a given 3D combustor configuration are modeled and reconstructed by means of a low-order dynamical system simulation. The source of nonlinearity is solely allocated to flame dynamics, saturating the growth of acoustic amplitudes, while the oscillation amplitudes are assumed to always remain within the linearity limit. First, a reduced order model (ROM) which reproduces the combustor's modal distribution and damping of acoustic oscillations is derived. The ROM is a low-order state-space system, which results from a projection of the linearized Euler equations (LEE) into their truncated eigenspace. Second, flame dynamics are modeled as a function of acoustic perturbations by means of a nonlinear transfer function. This function has a linear and a nonlinear contribution. The linear part is modeled analytically from first principles, while the nonlinear part is mathematically cast into a cubic saturation functional form. Additionally, the impact of stochastic forcing due to broadband combustion noise is included by additive white noise sources. Then, the acoustic and the flame system is interconnected, where thermoacoustic noncompactness due to the transversal modes' high frequency (HF) is accounted for by a distributed source term framework. The resulting nonlinear thermoacoustic system is solved in frequency and time domain. Linear growth rates predict linear stability, while envelope plots and probability density diagrams of the resulting pressure traces characterize the thermoacoustic performance of the combustor from a dynamical systems theory perspective. Comparisons against experimental data are conducted, which allow the rating of the flame modes in terms of their capability to reproduce the observed combustor dynamics. Ultimately, insight into the physics of high-frequency, transversal thermoacoustic systems is created.

Self-Excited High-Frequency Transverse Limit-Cycle Oscillations and Associated Flame Dynamics in a Gas Turbine Reheat Combustor Experiment

2021 ◽  
Author(s):  
Jonathan McClure ◽  
Frederik M. Berger ◽  
Michael Bertsch ◽  
Bruno Schuermans ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
Gas Turbine ◽  
Limit Cycle ◽  
High Frequency ◽  
Dynamic Pressure ◽  
High Amplitude ◽  
Limit Cycle Oscillations ◽  
Flame Dynamics ◽  
Auto Ignition

Abstract This paper presents the investigation of high-frequency thermoacoustic limit-cycle oscillations in a novel experimental gas turbine reheat combustor featuring both auto-ignition and propagation stabilised flame zones at atmospheric pressure. Dynamic pressure measurements at the faceplate of the reheat combustion chamber reveal high-amplitude periodic pressure pulsations at 3 kHz in the transverse direction of the rectangular cross-section combustion chamber. Further analysis of the acoustic signal shows that this is a thermoacoustically unstable condition undergoing limit-cycle oscillations. A sensitivity study is presented which indicates that these high-amplitude limit-cycle oscillations only occur under certain conditions: namely high power settings with propane addition to increase auto-ignition propensity. The spatially-resolved flame dynamics are then investigated using CH* chemiluminescence, phase-locked to the dynamic pressure, captured from all lateral sides of the reheat combustion chamber. This reveals strong heat release oscillations close to the chamber walls at the instability frequency, as well as axial movement of the flame tips in these regions and an overall transverse displacement of the flame. Both the heat release oscillations and the flame motion occur in phase with the acoustic mode. From these observations, likely thermoacoustic driving mechanisms which lead to the limit-cycle oscillations are inferred. In this case, the overall flame-acoustics interaction is assumed to be a superposition of several effects, with the observations suggesting strong influences from autoignition-pressure coupling as well as flame displacement and deformation due to the acoustic velocity field. These findings provide a foundation for the overall objective of developing predictive approaches to mitigate the impact of high-frequency thermoacoustic instabilities in future generations of gas turbines with sequential combustion systems.

scholarly journals The processes of vaporization in the porous structures working with the excess of liquid

2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 363-373 ◽  
Author(s):  
Alexander Genbach ◽  
Nellya Jamankulova ◽  
Vukman Bakic
Keyword(s):  
Temperature Difference ◽  
High Speed ◽  
Power Plants ◽  
Cooling System ◽  
Thermal Power ◽  
Laser System ◽  
Operating Conditions ◽  
Design Parameters ◽  
Porous Structures ◽  
The Impact

The processes of vaporization in porous structures, working with the excess of liquid are investigated. With regard to the thermal power plants new porous cooling system is proposed and investigated, in which the supply of coolant is conducted by the combined action of gravity and capillary forces. The cooling surface is made of stainless steel, brass, copper, bronze, nickel, alundum and glass, with wall thickness of (0.05-2)?10-3 m. Visualizations of the processes of vaporization were carried out using holographic interferometry with the laser system and high speed camera. The operating conditions of the experiments were: water pressures (0.01-10) MPa, the temperature difference of sub-cooling (0-20)?C, an excess of liquid (1-14) of the steam flow, the heat load (1-60)?104 W/m2, the temperature difference (1-60)?C and orientation of the system (? 0 - ? 90) degrees. Studies have revealed three areas of liquid vaporization process (transitional, developed and crisis). The impact of operating and design parameters on the integrated and thermal hydraulic characteristics was defined. The optimum (minimum) flow rate of cooling fluid and the most effective type of mesh porous structure were also defined.

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