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.

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

2009 ◽  
Author(s):  
Bruno Schuermans ◽  
Felix Guethe ◽  
Douglas Pennel ◽  
Daniel Guyot ◽  
Christian Oliver Paschereit
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Gas Turbine ◽  
Mass Flow ◽  
Equivalence Ratio ◽  
Transfer Functions ◽  
Optical Methods ◽  
Test Facility ◽  
Optical Technique ◽  
Acoustic Technique

Thermoacoustic transfer functions have been measured of a full-scale gas turbine burner operating at full engine pressure. Excitation of the high-pressure test facility was done using a siren that modulated 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 tubes and a light spectrometer. Three techniques to obtain the thermoacoustic transfer function are proposed and employed: two combined acoustical-optical technique 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. It only works, if heat release fluctuations in the flame have only one contribution, e.g. equivalence ratio or mass flow fluctuations. The second acoustic-optical 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 the methods is given. The measured transfer functions have been implemented into a non-linear, 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.

Measurement and Analysis of Flame Transfer Function in a Sector Combustor Under High Pressure Conditions

2003 ◽  
Author(s):  
W. S. Cheung ◽  
G. J. M. Sims ◽  
R. W. Copplestone ◽  
J. R. Tilston ◽  
C. W. Wilson ◽  
...  
Keyword(s):  
High Pressure ◽  
Transfer Function ◽  
Heat Release ◽  
Gas Turbine ◽  
Mass Flow ◽  
Atmospheric Pressure ◽  
Acoustic Waves ◽  
Gas Turbines ◽  
Transfer Functions ◽  
Unsteady Pressure

Lean premixed prevaporised (LPP) combustion can reduce NOx emissions from gas turbines, but often leads to combustion instability. A flame transfer function describes the change in the rate of heat release in response to perturbations in the inlet flow as a function of frequency. It is a quantitative assessment of the susceptibility of combustion to disturbances. The resulting fluctuations will in turn generate more acoustic waves and in some situations self-sustained oscillations can result. Flame transfer functions for LPP combustion are poorly understood at present but are crucial for predicting combustion oscillations. This paper describes an experiment designed to measure the flame transfer function of a simple combustor incorporating realistic components. Tests were conducted initially on this combustor at atmospheric pressure (1.2 bar and 550 K) to make an early demonstration of the combustion system. The test rig consisted of a plenum chamber with an inline siren, followed by a single LPP premixer/duct and a combustion chamber with a silencer to prevent natural instabilities. The siren was used to induce variable frequency pressure/acoustic signals into the air approaching the combustor. Both unsteady pressure and heat release measurements were undertaken. There was good coherence between the pressure and heat release signals. At each test frequency, two unsteady pressure measurements in the plenum were used to calculate the acoustic waves in this chamber and hence estimate the mass-flow perturbation at the fuel injection point inside the LPP duct. The flame transfer function relating the heat release perturbation to this mass flow was found as a function of frequency. The same combustor hardware and associated instrumentation were then used for the high pressure (15 bar and 800 K) tests. Flame transfer function measurements were taken at three combustion conditions that simulated the staging point conditions (Idle, Approach and Take-off) of a large turbofan gas turbine. There was good coherence between pressure and heat release signals at Idle, indicating a close relationship between acoustic and heat release processes. Problems were encountered at high frequencies for the Approach and Take-off conditions, but the flame transfer function for the Idle case had very good qualitative agreement with the atmospheric-pressure tests. The flame transfer functions calculated here could be used directly for predicting combustion oscillations in gas turbine using the same LPP duct at the same operating conditions. More importantly they can guide work to produce a general analytical model.

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.

Experimental Development of On-Line Flame Transfer Function Measurements for Fielded Gas Turbines

2021 ◽  
Author(s):  
Austin Matthews ◽  
Anna Cobb ◽  
Subodh Adhikari ◽  
David Wu ◽  
Tim Lieuwen ◽  
...  
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Gas Turbine ◽  
Gas Turbines ◽  
High Speed ◽  
Transfer Functions ◽  
Full Scale ◽  
Fuel Injector ◽  
Experimental Development ◽  
On Line

Abstract Understanding thermoacoustic instabilities is essential for the reliable operation of gas turbine engines. To complicate this understanding, the extreme sensitivity of gas turbine combustors can lead to instability characteristics that differ across a fleet. The capability to monitor flame transfer functions in fielded engines would provide valuable data to improve this understanding and aid in gas turbine operability from R&D to field tuning. This paper presents a new experimental facility used to analyze performance of full-scale gas turbine fuel injector hardware at elevated pressure and temperature. It features a liquid cooled, fiber-coupled probe that provides direct optical access to the heat release zone for high-speed chemiluminescence measurements. The probe was designed with fielded applications in mind. In addition, the combustion chamber includes an acoustic sensor array and a large objective window for verification of the probe using high-speed chemiluminescence imaging. This work experimentally demonstrates the new setup under scaled engine conditions, with a focus on operational zones that yield interesting acoustic tones. Results include a demonstration of the probe, preliminary analysis of acoustic and high speed chemiluminescence data, and high speed chemiluminescence imaging. The novelty of this paper is the deployment of a new test platform that incorporates full-scale engine hardware and provides the ability to directly compare acoustic and heat release response in a high-temperature, high-pressure environment to determine the flame transfer functions. This work is a stepping-stone towards the development of an on-line flame transfer function measurement technique for production engines in the field.

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.

Determination of an Empirical Transfer Function of a Solid Oxide Fuel Cell Gas Turbine Hybrid System Via Frequency Response Analysis

2009 ◽  
Vol 6 (3) ◽  
Author(s):  
Alex Tsai ◽  
Larry Banta ◽  
Larry Lawson ◽  
David Tucker
Keyword(s):  
Fuel Cell ◽  
Transfer Function ◽  
Solid Oxide Fuel Cell ◽  
Frequency Response ◽  
Gas Turbine ◽  
Transfer Functions ◽  
Solid Oxide ◽  
Test Facility ◽  
Oxide Fuel ◽  
Bode Plots

This paper presents the study of the effect variations in the heat effluence from a solid oxide fuel cell (SOFC) has on a gas turbine hybrid configuration. The SOFC is simulated through hardware at the U.S. Department of Energy, National Energy Technology Laboratory (NETL). The gas turbine, compressor, recuperative heat exchanger, and other balance of plant components are represented by actual hardware in the Hybrid Performance Test Facility at NETL. Fuel cell heat exhaust is represented by a combustor that is activated by a fuel cell model that computes energy release for various sensed system states System structure is derived by means of frequency response data generated by the sinusoidal oscillation of the combustor fuel valve over a range of frequencies covering three orders of magnitude. System delay and order are obtained from Bode plots of the magnitude and phase relationships between input and output parameters. Transfer functions for mass flow, temperature, pressure, and other states of interest are derived as a function of fuel valve flow, representative of fuel cell thermal effluent. The Bode plots can validate existing analytical transfer functions, provide steady state error detection, give a stability margin criterion for the fuel valve input, estimate system bandwidth, identify any nonminimum phase system behavior, pinpoint unstable frequencies, and serve as an element of a piecewise transfer function in the development of an overall transfer function matrix covering all system inputs and outputs of interest. Further loop shaping techniques and state space representation can be applied to this matrix in a multivariate control algorithm.

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.

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

2013 ◽  
Vol 136 (2) ◽  
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 spatiotemporal 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 equivalence ratio fluctuations in the reaction zone are measured spatially and temporally resolved 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.

Flame Response Mechanisms Due to Velocity Perturbations in a Lean Premixed Gas Turbine Combustor

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Brian Jones ◽  
Jong Guen Lee ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Gas Turbine ◽  
Velocity Fluctuation ◽  
Gas Turbine Combustor ◽  
Velocity Fluctuations ◽  
Inlet Velocity ◽  
Lean Premixed ◽  
Flame Response ◽  
Second Peak

The response of turbulent premixed flames to inlet velocity fluctuations is studied experimentally in a lean premixed, swirl-stabilized, gas turbine combustor. Overall chemiluminescence intensity is used as a measure of the fluctuations in the flame’s global heat release rate, and hot wire anemometry is used to measure the inlet velocity fluctuations. Tests are conducted over a range of mean inlet velocities, equivalence ratios, and velocity fluctuation frequencies, while the normalized inlet velocity fluctuation (V′/Vmean) is fixed at 5% to ensure linear flame response over the employed modulation frequency range. The measurements are used to calculate a flame transfer function relating the velocity fluctuation to the heat release fluctuation as a function of the velocity fluctuation frequency. At low frequency, the gain of the flame transfer function increases with increasing frequency to a peak value greater than 1. As the frequency is further increased, the gain decreases to a minimum value, followed by a second smaller peak. The frequencies at which the gain is minimum and achieves its second peak are found to depend on the convection time scale and the flame’s characteristic length scale. Phase-synchronized CH∗ chemiluminescence imaging is used to characterize the flame’s response to inlet velocity fluctuations. The observed flame response can be explained in terms of the interaction of two flame perturbation mechanisms, one originating at flame-anchoring point and propagating along the flame front and the other from vorticity field generated in the outer shear layer in the annular mixing section. An analysis of the phase-synchronized flame images show that when both perturbations arrive at the flame at the same time (or phase), they constructively interfere, producing the second peak observed in the gain curves. When the perturbations arrive at the flame 180 degrees out-of-phase, they destructively interfere, producing the observed minimum in the gain curve.

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