Analysis of Measured Flame Transfer Functions With Locally Resolved Density Fluctuation and OH-Chemiluminescence Data

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Johannes Peterleithner ◽  
Nicolai V. Stadlmair ◽  
Jakob Woisetschläger ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
Density Fluctuation ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Periodic Oscillation ◽  
Global Scale ◽  
Laser Vibrometry ◽  
Annular Jet ◽  
Partially Premixed ◽  
Hot Products

The goal of this study is to analyze flame transfer functions (FTFs) locally by quantifying the heat release rate with OH*-chemiluminescence and density fluctuation measurements using laser vibrometry. In this study, both techniques are applied to a swirl burner configuration with known FTFs acquired by multimicrophone-method (MMM) measurements for perfectly premixed and partially premixed cases. The planar fields of the quantities are compared to the FTFs in order to improve the understanding regarding the specific amplitude and phase values. On the global scale values of heat release expected from the MMM are satisfactorily reproduced by both methods for the premixed cases, whereas OH*-chemiluminescence data cannot be used as indicator for heat release in the partially premixed case, where equivalence ratio fluctuations are present. Vibrometry is not affected by fluctuations of equivalence ratio but additionally reveals the periodic oscillation of the conical annular jet of the cold reactants in the combustor filled with hot products.

Analysis of Measured Flame Transfer Functions With Locally Resolved Density Fluctuation and OH-Chemiluminescence Data

2015 ◽  
Author(s):  
Johannes Peterleithner ◽  
Nicolai V. Stadlmair ◽  
Jakob Woisetschläger ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
Density Fluctuation ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Rotational Symmetry ◽  
Periodic Oscillation ◽  
Density Fluctuations ◽  
Combustion Noise ◽  
Line Of Sight ◽  
Laser Vibrometer

The goal of the study presented in this paper is to analyze flame transfer functions with a new approach based on the combination of-line-of sight OH*-chemiluminescence and density fluctuation data. The OH*-chemiluminescence is acquired with a photomultiplier and an intensified camera, the density fluctuations are measured with a Laser vibrometer on a two axis traverse. In flames with forcing the acoustic fluctuations can be extracted from the data by discrimination of all contributions from combustion noise, because it is not correlated with the excitation device. Assuming rotational symmetry of the fluctuations originating from excitation, planar phase-resolved and pseudo-local OH*-chemiluminescence and density fluctuation data is obtained from the measured line-of-sight integrated signals. In the study this technique is applied to a swirl burner configuration with FTFs from known multi-microphone measurements (MMM). In the first step, the externally premixed mode without equivalence ratio fluctuations is studied and in the second step the fuel is injected in the swirler in order to generate equivalence ratio waves. At selected frequencies the planar fields of the OH*-chemiluminescence and density fluctuations are compared to the FTFs in order to improve the understanding regarding the specific amplitude and phase values. In addition to heat release the vibrometer data reveals the periodic oscillation of the conical annular jet of the cold reactants in the combustor filled with hot products. On the global scale the amplitudes and phases of heat release expected from the MMM are satisfactorily reproduced by both methods for the premixed cases, whereas OH*-chemiluminescence data cannot be used as indicator for heat release if equivalence ratio fluctuations are present, because the amplitude of the FTF is significantly over-predicted due to the sensitivity of OH* on the local fuel-air mixture.

Optical Measurement of Local and Global Transfer Functions for Equivalence Ratio Fluctuations in a Turbulent Swirl Flame

2013 ◽  
Author(s):  
Bernhard C. Bobusch ◽  
Bernhard Ćosić ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Optical Measurement ◽  
Low Frequencies ◽  
Fuel Flow ◽  
Calibration Measurement

Equivalence ratio fluctuations are known to be one of the key factors controlling thermoacoustic stability in lean premixed gas turbine combustors. The mixing and thus the spatio-temporal evolution of these perturbations in the combustor flow is, however, difficult to account for in present low-order modeling approaches. To investigate this mechanism, experiments in an atmospheric combustion test rig are conducted. To assess the importance of equivalence ratio fluctuations in the present case, flame transfer functions for different injection positions are measured. By adding known perturbations in the fuel flow using a solenoid valve, the influence of equivalence ratio oscillations on the heat release rate is investigated. The spatially and temporally resolved equivalence ratio fluctuations in the reaction zone are measured using two optical chemiluminescence signals, captured with an intensified camera. A steady calibration measurement allows for the quantitative assessment of the equivalence ratio fluctuations in the flame. This information is used to obtain a mixing transfer function, which relates fluctuations in the fuel flow to corresponding fluctuations in the equivalence ratio of the flame. The current study focuses on the measurement of the global, spatially integrated, transfer function for equivalence ratio fluctuations and the corresponding modeling. In addition, the spatially resolved mixing transfer function is shown and discussed. The global mixing transfer function reveals that despite the good spatial mixing quality of the investigated generic burner, the ability to damp temporal fluctuations at low frequencies is rather poor. It is shown that the equivalence ratio fluctuations are the governing heat release rate oscillation response mechanism for this burner in the low-frequency regime. The global transfer function for equivalence ratio fluctuations derived from the measurements is characterized by a pronounced low-pass characteristic, which is in good agreement with the presented convection–diffusion mixing model.

Optical Transfer Function Measurements for Technically Premixed Flames

2008 ◽  
Author(s):  
Bruno Schuermans ◽  
Felix Guethe ◽  
Wolfgang Mohr
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Inverse Method ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Acoustic Method ◽  
Full Scale ◽  
Optical Transfer Function ◽  
Information Measurement ◽  
Combustion Systems

This paper deals with a novel approach for measuring thermo-acoustic transfer functions. These transfer functions are essential to predict the acoustic behavior of gas turbine combustion systems. Thermoacoustic prediction has become an essential step in the development process of low-NOx combustion systems. The proposed method is particularly useful in harsh environments. It makes use of simultaneous measurement of the chemiluminescence of different species in order to obtain the heat release fluctuations via an inverse method. Generally, the heat release fluctuation has two contributions: one due to equivalence ratio fluctuations, the other due to modulations of mass flow of mixture entering the reaction zone. Because the chemiluminescence of one single species depends differently on the two contributions, it is not possible to quantitatively estimate the heat based on this information. Measurement of the transfer matrix based on a purely acoustic method provides quantitative results, independent of the nature of the interaction mechanism. However, this method is difficult to apply in industrial full-scale experiments. The method developed in this work uses the chemiluminescence time traces of several species. After calibration, an over-determined inverse method is used to calculate the two heat release contributions from the time traces. The optical method proposed here has the advantage that it does not only provide quantitative heat release fluctuations, but it also quantifies the underlying physical mechanisms that cause the heat release fluctuations: it shows what part of the heat release is caused by equivalence ratio fluctuations and what part by flame front dynamics. The method has been tested on a full scale, swirl stabilized gas turbine burner. Comparison with a purely acoustic method validated the concept.

Comparison of Flame Transfer Functions Acquired by Chemiluminescence and Density Fluctuation

2016 ◽  
Author(s):  
Johannes Peterleithner ◽  
Riccardo Basso ◽  
Franz Heitmeir ◽  
Jakob Woisetschläger ◽  
Raimund Schlüßler ◽  
...  
Keyword(s):  
Equivalence Ratio ◽  
Transfer Functions ◽  
Turbulent Flame ◽  
Time Derivative ◽  
Density Fluctuations ◽  
Time Resolved ◽  
Partially Premixed Flames ◽  
Partially Premixed ◽  
Premixed Turbulent Flame ◽  
First Time

The goal of this study was to measure the Flame Transfer Function of a perfectly and a partially premixed turbulent flame by means of Laser Interferometric Vibrometry. For the first time, this technique is used to detect integral heat release fluctuations. The results were compared to classical OH*-chemiluminescence measurements. Effects of equivalence ratio waves and vortex rollup were found within those flames and were then investigated by means of time resolved planar CH*/OH*-chemiluminescence and Frequency modulated Doppler global velocimetry. This work is motivated by the difficulties chemiluminescence encounters when faced with partially premixed flames including equivalence ratio waves and flame stretching. LIV, recording the time derivative of the density fluctuations as line-of-sight data, is not affected by these flame properties.

Thermoacoustic Modeling of a Gas Turbine Using Transfer Functions Measured Under Full Engine Pressure

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Bruno Schuermans ◽  
Felix Guethe ◽  
Douglas Pennell ◽  
Daniel Guyot ◽  
Christian Oliver Paschereit
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Gas Turbine ◽  
Mass Flow ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Test Facility ◽  
Optical Technique ◽  
Optical Techniques ◽  
Acoustic Technique

Thermoacoustic transfer functions of a full-scale gas turbine burner operating under full engine pressure have been measured. The excitation of the high-pressure test facility was done using a siren that modulated a part of the combustion airflow. Pulsation probes have been used to record the acoustic response of the system to this excitation. In addition, the flame’s luminescence response was measured by multiple photomultiplier probes and a light spectrometer. Three techniques to obtain the thermoacoustic transfer function are proposed and employed: two acoustic-optical techniques and a purely acoustic technique. The first acoustical-optical technique uses one single optical signal capturing the chemiluminescence intensity of the flame as a measure for the heat release in the flame. This technique only works if heat release fluctuations in the flame have only one generic source, e.g., equivalence ratio or mass flow fluctuations. The second acoustic-optical technique makes use of the different response of the flame’s luminescence at different optical wavelengths bands to acoustic excitation. It also works, if the heat release fluctuations have two contributions, e.g., equivalence ratio and mass flow fluctuation. For the purely acoustic technique, a new method was developed in order to obtain the flame transfer function, burner transfer function, and flame source term from only three pressure transducer signals. The purely acoustic method could be validated by the results obtained from the acoustic-optical techniques. The acoustic and acoustic-optical methods have been compared and a discussion on the benefits and limitations of each is given. The measured transfer functions have been implemented into a nonlinear, three-dimensional, time domain network model of a gas turbine with an annular combustion chamber. The predicted pulsation behavior shows a good agreement with pulsation measurements on a field gas turbine.

Laser vibrometry for combustion diagnostics in thermoacoustic research

2015 ◽  
Vol 82 (11) ◽  
Author(s):  
Johannes Peterleithner ◽  
Jakob Woisetschläger
Keyword(s):  
Heat Release ◽  
Density Fluctuation ◽  
Fluid Velocity ◽  
Density Fluctuations ◽  
Laser Doppler ◽  
Acoustic Oscillations ◽  
Laser Vibrometry ◽  
Laser Doppler Vibrometry ◽  
Novel Technique ◽  
Combustion Diagnostics

AbstractA novel technique for time- and space-resolved measurement of density fluctuation is presented. It is nonintrusive and based on laser Doppler vibrometry. The density fluctuations reveal information on dynamic heat release and fluid velocity. The significance of this technique is proven by recording thermo-acoustic oscillations in a model combustor.

Reconstruction of the Heat Release Response of Partially Premixed Flames

2010 ◽  
Author(s):  
Kyu Tae Kim ◽  
Jong Guen Lee ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca
Keyword(s):  
Heat Release ◽  
Phase Difference ◽  
Equivalence Ratio ◽  
Forced Response ◽  
Premixed Flame ◽  
Physical Parameters ◽  
Ir Absorption ◽  
Inlet Velocity ◽  
Partially Premixed ◽  
Partially Premixed Flame

The forced response of a swirl-stabilized, partially premixed flame to inlet velocity and equivalence ratio oscillations was experimentally investigated in a model lean-premixed gas turbine combustor. Three different forcing mechanisms were studied: the response of a premixed flame to velocity oscillations, the response of a partially premixed flame to equivalence ratio oscillations, and the response of a partially premixed flame to velocity and equivalence ratio oscillations. The overall heat release response of the flame was determined from measurements of the CH* chemiluminescence emission intensity from the entire flame, while the response of the spatially distributed heat release was determined from phase-synchronized chemiluminescence images. In addition, simultaneous measurements were made of the inlet velocity and equivalence ratio oscillations using the two-microphone method and the IR absorption technique, respectively. The results show that in the linear regime, the response of a partially premixed flame to simultaneous velocity and equivalence ratio oscillations can be reconstructed from independent measurements of the flame’s response to velocity oscillations and to equivalence ratio oscillations using a vector summation method. This is the first experimental demonstration of a two-input one-output model of a swirl-stabilized partially premixed flame. It suggests that the response of a partially premixed flame is governed by four physical parameters, i.e., the oscillation frequency, the amplitude of velocity oscillation, the amplitude of equivalence ratio oscillation, and the phase difference between the two oscillations. As a result, the heat release response of a partially premixed flame can be amplified or damped, depending on the phase difference between the velocity and equivalence ratio oscillations at the combustor inlet.

Optical Transfer Function Measurements for Technically Premixed Flames

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Bruno Schuermans ◽  
Felix Guethe ◽  
Wolfgang Mohr
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Inverse Method ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Acoustic Method ◽  
Full Scale ◽  
Optical Transfer Function ◽  
Information Measurement ◽  
Combustion Systems

This paper deals with a novel approach for measuring thermoacoustic transfer functions. These transfer functions are essential to predict the acoustic behavior of gas turbine combustion systems. Thermoacoustic prediction has become an essential step in the development process of low NOx combustion systems. The proposed method is particularly useful in harsh environments. It makes use of simultaneous measurement of the chemiluminescence of different species in order to obtain the heat release fluctuations via inverse method. Generally, the heat release fluctuation has two contributions: one due to equivalence ratio fluctuations, and the other due to modulations of mass flow of mixture entering the reaction zone. Because the chemiluminescence of one single species depends differently on the two contributions, it is not possible to quantitatively estimate the heat based on this information. Measurement of the transfer matrix based on a purely acoustic method provides quantitative results, independent of the nature of the interaction mechanism. However, this method is difficult to apply in industrial full-scale experiments. The method developed in this work uses the chemiluminescence time traces of several species. After calibration, an overdetermined inverse method is used to calculate the two heat release contributions from the time traces. The optical method proposed here has the advantage that it does not only provide quantitative heat release fluctuations but it also quantifies the underlying physical mechanisms that cause the heat release fluctuations: It shows what part of the heat release is caused by equivalence ratio fluctuations and what part by flame front dynamics. The method was tested on a full scale swirl-stabilized gas turbine burner. Comparison with a purely acoustic method validated the concept.

A Detailed Analysis of Thermoacoustic Interaction Mechanisms in a Turbulent Premixed Flame

2004 ◽  
Author(s):  
Bruno Schuermans ◽  
Valter Bellucci ◽  
Felix Guethe ◽  
Franc¸ois Meili ◽  
Peter Flohr ◽  
...  
Keyword(s):  
Heat Release ◽  
Acoustic Field ◽  
Turbulence Intensity ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Turbulent Flame ◽  
Interaction Mechanism ◽  
Flame Speed ◽  
Fuel Concentration ◽  
Turbulent Flame Speed

A combined theoretical and experimental analysis of thermoacoustic interaction mechanisms of a lean pre-mixed swirl-stabilized gas turbine burner is presented. A full-scale gas turbine burner has been tested in an atmospheric test rig. The test facility was equipped with loudspeakers to excite the acoustic field and with arrays of microphones to measure the response of the acoustic field to the forcing signal. With this set-up transfer matrices relating the acoustic pressure and velocity on both sides of the flame front have been measured. A laser absorption measurement technique allowed for measurement of the fluctuations of fuel concentration in the mixture. Heat release fluctuations were monitored using a photo-multiplier. The measurement of the acoustic field, heat release and equivalence ratio fluctuations have been measured simultaneously. Special attention has been given to the role of fuel concentration fluctuations in the thermoacoustic interaction mechanism. In order to be able to clearly separate this mechanism from other possible mechanisms, all the experiments have been performed in pre-premixing mode as well. In pre-premixing mode the fuel is injected far upstream of the burner in order to avoid fuel concentration fluctuations at the burner location. This is in contrast with premixing mode where fuel and air are mixed in the burner. An acoustic flame model has been derived. The model includes the well-known interaction mechanism of equivalence ratio fluctuations but also includes a novel mechanism that is caused by fluctuations of vorticity. This latter mechanism relates the turbulent flame speed via turbulence intensity fluctuations to the acoustic field. The idea is that periodic acoustic fluctuations cause periodic changes of the turbulence intensity. The turbulence intensity strongly affects the turbulence flame speed. The fluctuations of the turbulent flame speed result in fluctuations of the heat release. This turbulence intensity fluctuation model has been compared with the measured pre-premix transfer functions and shows an excellent agreement. The measured transfer functions in premix mode have been compared with the model that includes fluctuations of fuel concentration and turbulence intensity. Also in this case a very good agreement is found. Moreover, it has been demonstrated that the phase relation between measured equivalence ratio fluctuation and heat release corresponds to the model.

scholarly journals Modelling the generation of temperature inhomogeneities by a premixed flame

2017 ◽  
Vol 10 (2) ◽  
pp. 111-130 ◽  
Author(s):  
Thomas Steinbacher ◽  
Max Meindl ◽  
Wolfgang Polifke
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Release ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Mixture Fraction ◽  
Transport Processes ◽  
Premixed Flame ◽  
Series Data ◽  
Entropy Transfer

The response of a laminar, premixed flame to perturbations of upstream equivalence ratio is investigated and modelled, with emphasis on the generation of ‘entropy waves’, i.e. entropic inhomogeneities of downstream temperature. Transient computational fluid dynamics simulations of two adiabatic lean methane-air flames of different Péclet numbers provide guidance and validation data for subsequent modelling. The respective entropy transfer functions, which describe the production of temperature inhomogeneities, as well as transfer functions for the variation of the heat release, are determined from the computational fluid dynamics time series data by means of system identification. The processes governing the dynamics of the entropy transfer functions are segregated into two sub-problems: (1) heat release due to chemical reaction at the flame front and (2) advective and diffusive transport. By adopting a formulation in terms of a mixture fraction variable, these two sub-problems can be treated independently from each other. Models for both phenomena are derived and analysed using simple 0- and 1-dimensional configurations. The heat release process (1) is represented by a fast-reaction-zone model, which takes into account variations of the specific heat capacity with equivalence ratio in order to evaluate the magnitude of downstream temperature fluctuations with quantitative accuracy. For the transport processes (2), two types of models based on mean field data from the computational fluid dynamics simulation are proposed: A semi-analytical, low-order formulation based on stream lines, and a state-space formulation, which is constructed by Finite Elements discretisation of the transport equation for mixture fraction. Model predictions for the entropy transfer functions are found to agree well with the computational fluid dynamics reference data at very low computational costs.

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