An Experimental Investigation of the Nonlinear Response of an Atmospheric Swirl-Stabilized Premixed Flame

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
Sebastian Schimek ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Gas Turbines ◽  
Oscillation Amplitude ◽  
Network Models ◽  
Mean Flow ◽  
Test Rig ◽  
Linear Network ◽  
Modeling Tools ◽  
Velocity Fluctuations ◽  
Thermoacoustic Instabilities ◽  
Flame Response

Due to stringent emission restrictions, modern gas turbines mostly rely on lean premixed combustion. Since this combustion mode is susceptible to thermoacoustic instabilities, there is a need for modeling tools with predictive capabilities. Linear network models are able to predict the occurrence of thermoacoustic instabilities but yield no information on the oscillation amplitude. The prediction of the pulsation levels and hence an estimation whether a certain operating condition has to be avoided is only possible if information on the nonlinear flame response is available. Typically, the flame response shows saturation at high forcing amplitudes. A newly constructed atmospheric test rig, specifically designed for the realization of high excitation amplitudes over a broad frequency range, is used to generate extremely high acoustic forcing power with velocity fluctuations of up to 100% of the mean flow. The test rig consists of a generic combustor with a premixed swirl-stabilized natural gas flame, where the upstream part has a variable length to generate adaptive resonances of the acoustic field. The OH∗ chemiluminescence response, with respect to velocity fluctuations at the burner, is measured for various excitation frequencies and amplitudes. From these measurements, an amplitude dependent flame transfer function is obtained. Phase-averaged OH∗ pictures are used to identify changes in the flame shape related to saturation mechanisms. For different frequency regimes, different saturation mechanisms are identified.

An Experimental Investigation of the Nonlinear Response of an Atmospheric Swirl-Stabilized Premixed Flame

2010 ◽  
Author(s):  
Sebastian Schimek ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Gas Turbines ◽  
Oscillation Amplitude ◽  
Network Models ◽  
Mean Flow ◽  
Test Rig ◽  
Linear Network ◽  
Modeling Tools ◽  
Velocity Fluctuations ◽  
Thermoacoustic Instabilities ◽  
Flame Response

Due to stringent emission restrictions, modern gas turbines mostly rely on lean premixed combustion. Since this combustion mode is susceptible to thermoacoustic instabilities, there is a need for modeling tools with predictive capabilities. Linear network models are able to predict the occurrence of thermoacoustic instabilities but yield no information on the oscillation amplitude. The prediction of the pulsation levels and hence an estimation whether a certain operating condition has to be avoided is only possible if information on the nonlinear flame response is available. Typically, the flame response shows saturation at high forcing amplitudes. A newly constructed atmospheric test rig, specifically designed for the realization of high excitation amplitudes over a broad frequency range, is used to generate extremely high acoustic forcing power with velocity fluctuations of up to 100% of the mean flow. The test rig consists of a generic combustor with a premixed swirl-stabilized natural gas flame, where the upstream part has a variable length to generate adaptive resonances of the acoustic field. The OH* chemiluminescence response, with respect to velocity fluctuations at the burner is measured for various excitation frequencies and amplitudes. From these measurements, an amplitude dependent flame transfer function is obtained. Phase-averaged OH* pictures are used to identify changes in the flame shape related to saturation mechanisms. For different frequency regimes, different saturation mechanisms are identified.

Amplitude-Dependent Flow Field and Flame Response to Axial and Tangential Velocity Fluctuations

2012 ◽  
Author(s):  
Sebastian Schimek ◽  
Bernhard Ćosić ◽  
Jonas P. Moeck ◽  
Steffen Terhaar ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Amplitude Dependence ◽  
Mean Flow ◽  
Modeling Tools ◽  
Velocity Fluctuations ◽  
Flame Response ◽  
The Mean

Lean premixed combustion is prone to thermoacoustic instabilities. These mostly self-excited instabilities are caused by a feedback mechanism between the acoustic field, hydrodynamic structures, and the heat release rate in the flame. While various modeling tools are available for the linear analysis of thermoacoustic systems, a detailed knowledge of the governing nonlinearities, responsible for the saturation in the flame response, is still missing. The fundamental understanding of the flow field–heat release interaction is of crucial importance for the prediction of the pressure oscillation amplitude. To improve the understanding of these interaction processes, the current paper investigates the nonlinear interaction of the flow field and the unsteady heat release rate and the role of swirl fluctuations. The test rig that is used in the present work consists of a generic swirl-stabilized combustor fed with natural gas and equipped with a high-amplitude forcing device. The influence of the phase between axial and azimuthal velocity oscillations is assessed on the basis of the amplitude and phase relations between the velocity fluctuations at the inlet and the outlet of the burner. These relations are determined in the experiment with the Multi-Microphone-Method and a two component laser-Doppler velocimeter. Particle image velocimetry and OH*-chemiluminescence measurements are conducted to study the interaction between the flow field and the flame. For several frequency regimes, characteristic properties of the forced flow field and flame are identified, and a strong amplitude dependence is observed. It is found that the convective time delay between the swirl generator and the flame has an important influence on swirl-number oscillations and the flame dynamics in the low-frequency regime. For mid and high frequencies, significant changes in the mean flow field and the mean flame position are identified for high forcing amplitudes. These affect the interaction between coherent structures and the flame and are suggested to be responsible for the saturation in the flame response at high forcing amplitudes.

scholarly journals Methods for the Calculation of Thermoacoustic Stability Boundaries and Monte Carlo-Free Uncertainty Quantification

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Georg A. Mensah ◽  
Luca Magri ◽  
Jonas P. Moeck
Keyword(s):  
Monte Carlo ◽  
Uncertainty Quantification ◽  
Gas Turbines ◽  
Network Models ◽  
System Stability ◽  
Model Parameters ◽  
Geometrical Parameters ◽  
Parameter Uncertainties ◽  
Flame Response ◽  
Mode Stability

Thermoacoustic instabilities are a major threat for modern gas turbines. Frequency-domain-based stability methods, such as network models and Helmholtz solvers, are common design tools because they are fast compared to compressible flow computations. They result in an eigenvalue problem, which is nonlinear with respect to the eigenvalue. Thus, the influence of the relevant parameters on mode stability is only given implicitly. Small changes in some model parameters, may have a great impact on stability. The assessment of how parameter uncertainties propagate to system stability is therefore crucial for safe gas turbine operation. This question is addressed by uncertainty quantification. A common strategy for uncertainty quantification in thermoacoustics is risk factor analysis. One general challenge regarding uncertainty quantification is the sheer number of uncertain parameter combinations to be quantified. For instance, uncertain parameters in an annular combustor might be the equivalence ratio, convection times, geometrical parameters, boundary impedances, flame response model parameters, etc. A new and fast way to obtain algebraic parameter models in order to tackle the implicit nature of the problem is using adjoint perturbation theory. This paper aims to further utilize adjoint methods for the quantification of uncertainties. This analytical method avoids the usual random Monte Carlo (MC) simulations, making it particularly attractive for industrial purposes. Using network models and the open-source Helmholtz solver PyHoltz, it is also discussed how to apply the method with standard modeling techniques. The theory is exemplified based on a simple ducted flame and a combustor of EM2C laboratory for which experimental data are available.

On the Use of Thermoacoustic Analysis for Robust Burner Design

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Valter Bellucci ◽  
Dariusz Nowak ◽  
Weiqun Geng ◽  
Christian Steinbach
Keyword(s):  
First Generation ◽  
Transfer Functions ◽  
Three Dimensional ◽  
Development Program ◽  
Network Models ◽  
Limiting Factor ◽  
Thermoacoustic Instabilities ◽  
Flame Response ◽  
Burner Design ◽  
Analysis Mode

Advanced thermoacoustic analysis is now routinely used in gas turbine combustor development. A thermoacoustic approach based on a combination of numerical analysis (CFD and three-dimensional acoustics), acoustic network models, and dedicated measurements of acoustic flame response is well accepted across the industry. However, its application to specific combustor upgrade or development programs in “prediction mode” as opposed to “analysis mode” remains a challenge. This is mainly due to the large sensitivity of the complex methodology to key inputs, such as flame transfer functions, that can be only predicted in the burner design phase. This paper discusses an example where we made an effort to apply the thermoacoustic approach in predictive mode. The example refers to the upgrade of a first generation diffusion burner with a partially premix burner to achieve low emissions. Thermoacoustic instabilities were predicted as a limiting factor for combustor operation and thus a design parameter was identified to perform the thermoacoustic combustor tuning at engine level. A particular challenge of this development program was that no test rig was available. Therefore, the new premix burner was directly installed into a field engine where it was successfully tested.

Commissioning of a Test Rig for Auto-Ignition Delay Time Measurements on Kerosene Based Fuel Paper

2001 ◽  
Author(s):  
W. S. Cheung ◽  
J. R. Tilston
Keyword(s):  
Ignition Delay ◽  
Delay Time ◽  
Gas Turbines ◽  
Ignition Delay Time ◽  
Operating Experience ◽  
Ignition Process ◽  
Mean Flow ◽  
Test Rig ◽  
Auto Ignition ◽  
Technical Risks

A thorough understanding of the auto-ignition process is critical to the success of lean premixed prevapourised (LPP) combustors for future ultra-low NOx emissions gas turbines. A considerable amount of work has been done in the past on auto-ignition delay time (ADT) measurements for various aviation fuels and hydrocarbons. However, little was known about the influence of various possible fuel additives on ADT. A test rig was designed and built by DERA specifically for ADT measurements. It consisted of an injector housing and an instrumented duct where the ignition location could be monitored by fibre optic sensors. It was intended to acquire ADT measurements at 875K, 16bar and 40m/s of mean flow. The test rig and instrumentation were commissioned in January and February 2000. However, instrumentation inside the injector housing was damaged soon after the initial hot run as a result of overheating. Attempts were made to repair the damaged components and to identify the cause of overheating. Unfortunately, the damage to the components was extensive and the cause of overheating could not be diagnosed. In view of the technical risks involved, it was decided to stop further testing with this rig. Although ADT measurements could not be undertaken as planned, useful operating experience was gained from the tests conducted.

scholarly journals Weakly nonlinear analysis of thermoacoustic instabilities in annular combustors

2016 ◽  
Vol 805 ◽  
pp. 52-87 ◽  
Author(s):  
G. Ghirardo ◽  
M. P. Juniper ◽  
J. P. Moeck
Keyword(s):  
Gas Turbines ◽  
Practical Importance ◽  
Industrial Applications ◽  
Local Pressure ◽  
Weakly Nonlinear ◽  
Acoustic Damping ◽  
Thermoacoustic Instabilities ◽  
Rotationally Symmetric ◽  
Flame Response ◽  
Annular Combustor

Rotationally symmetric annular combustors are of practical importance because they generically resemble combustion chambers in gas turbines, in which thermoacoustically driven oscillations are a major concern. We focus on azimuthal thermoacoustic oscillations and model the fluctuating heat release rate as being dependent only on the local pressure in the combustion chamber. We study the dynamics of the annular combustor with a finite number of compact flames equispaced around the annulus, and characterize the flames’ response with a describing function. We discuss the existence, amplitude and the stability of standing and spinning waves, as a function of: (i) the number of the burners; (ii) the acoustic damping in the chamber; (iii) the flame response. We present the implications for industrial applications and the future direction of investigations. We then present as an example the first theoretical study of thermoacoustic triggering in annular combustors, which shows that rotationally symmetric annular chambers that are thermoacoustically unstable do not experience only stable spinning solutions, but can also experience stable standing solutions. We finally test the theory on one experiment with good agreement.

Amplitude-Dependent Flow Field and Flame Response to Axial and Tangential Velocity Fluctuations

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Sebastian Schimek ◽  
Bernhard Ćosić ◽  
Jonas P. Moeck ◽  
Steffen Terhaar ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Tangential Velocity ◽  
Azimuthal Velocity ◽  
Forced Flow ◽  
Laser Doppler Velocimeter ◽  
Amplitude Dependence ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
Flame Response ◽  
The Mean

The current paper investigates the nonlinear interaction of the flow field and the unsteady heat release rate and the role of swirl fluctuations. The test rig consists of a generic swirl-stabilized combustor fed with natural gas and equipped with a high-amplitude forcing device. The influence of the phase between axial and azimuthal velocity oscillations is assessed on the basis of the amplitude and phase relations between the velocity fluctuations at the inlet and the outlet of the burner. These relations are determined in the experiment with the multimicrophone-method and a two component laser Doppler velocimeter (LDV). Particle image velocimetry (PIV) and OH*-chemiluminescence measurements are conducted to study the interaction between the flow field and the flame. For several frequency regimes, characteristic properties of the forced flow field and flame are identified, and a strong amplitude dependence is observed. It is found that the convective time delay between the swirl generator and the flame has an important influence on swirl-number oscillations and the flame dynamics in the low-frequency regime. For mid and high frequencies, significant changes in the mean flow field and the mean flame position are identified for high forcing amplitudes. These affect the interaction between coherent structures and the flame and are suggested to be responsible for the saturation in the flame response at high forcing amplitudes.

Investigation of Thermoacoustic Stability Limits of an Annular Gas Turbine Combustor Test-Rig With and Without Helmholtz-Resonators

2005 ◽  
Author(s):  
Joachim Lepers ◽  
Werner Krebs ◽  
Bernd Prade ◽  
Patrick Flohr ◽  
Giacomo Pollarolo ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Thermal Power ◽  
Power Input ◽  
Test Rig ◽  
Combustion Chambers ◽  
Thermoacoustic Instabilities ◽  
Helmholtz Resonators ◽  
Annular Combustor ◽  
Computational Analyses

Providing gas turbine combustion chambers with Helmholtz-resonators is a promising approach for extending the operating range of gas turbines towards higher thermal power input whilst minimizing the risk of thermoacoustic instabilities. The work currently being reported gives an overview of experimental and computational analyses carried out for a full annular combustor test-rig located at Gioia del Colle in Italy. The thermoacoustic stability characteristics of this test-rig were thoroughly analyzed both for a base configuration without Helmholtz-resonators and for an extended configuration with 14 Helmholtz-resonators. An increase of power input to the combustor by 8.5–20% can be realized when the test-rig is equipped with resonators. The experimental analyses are reproduced by a computational model.

Ranking of Aircraft Fuel-Injectors Regarding Low Frequency Thermoacoustics Based on an Energy Balance Method

2021 ◽  
Author(s):  
André Fischer ◽  
Claus Lahiri
Keyword(s):  
Energy Balance ◽  
Low Frequency ◽  
Network Models ◽  
Operating Conditions ◽  
Balance Method ◽  
Energy Balance Method ◽  
Fuel Injectors ◽  
Thermoacoustic Instabilities ◽  
Aircraft Fuel ◽  
Flame Response

Abstract Many modern low emission combustion systems suffer from thermoacoustic instabilities, which may lead to customer irritation (noise) or engine damages. The prediction of the frequency response of the flame is oftentimes not straightforward, so that it is common practice to measure the flame response in an experiment. The outcome of the measurement is typically a flame transfer-function (FTF), which can be used in low order acoustic network models to represent the flame. This paper applies an alternative criterion to evaluate the potential of the flame to become instable, the flame-amplification factor (FAF). It is based on an energy balance method and can be directly derived from the measured flame-transfer-matrix (FTM). In order to demonstrate this approach two different kerosene-driven aircraft fuel injectors were measured in the Rolls-Royce SCARLET rig in a single-sector RQL-combustor under realistic operating conditions. Here the multi-microphone method has been applied with acoustic forcing from up- and downstream side to determine the FTM. In contrast to the FTF-approach the full FTM data has been post-processed to derive the FAF. The FAF is then successfully used to rank the fuel injectors regarding their low frequency thermo-acoustic behaviour, because it is proportional to amplitudes of self-excited frequencies in FANN-rig (full annular) configuration.

Using Thermoacoustic Analysis for Robust Burner Design

2007 ◽  
Author(s):  
Valter Bellucci ◽  
Dariusz Nowak ◽  
Weiqun Geng ◽  
Christian Steinbach
Keyword(s):  
First Generation ◽  
Transfer Functions ◽  
Three Dimensional ◽  
Development Program ◽  
Network Models ◽  
Limiting Factor ◽  
Thermoacoustic Instabilities ◽  
Flame Response ◽  
Burner Design ◽  
Analysis Mode

Advanced thermoacoustic analysis is now routinely used in gas turbine combustor development. A thermoacoustic approach based on a combination of numerical analysis (CFD and three-dimensional acoustics), acoustic network models and dedicated measurements of acoustic flame response is well accepted across the industry. However, its application to specific combustor upgrade or development programs in “prediction mode” as opposed to “analysis mode” remains a challenge. This is mainly due to the large sensitivity of the complex methodology to key inputs, such as flame transfer functions, that can be only predicted in the burner design phase. This paper discusses an example where we made an effort to apply the thermoacoustic approach in predictive mode. The example refers to the upgrade of a first generation diffusion burner with a partially premix burner to achieve low emissions. Thermoacoustic instabilities were predicted as a limiting factor for combustor operation and thus a design parameter was identified to perform the thermoacoustic combustor tuning at engine level. A particular challenge of this development program was that no test rig was available. Therefore, the new premix burner was directly installed into a field engine where it was successfully tested.

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