Thermoacoustic Analysis of Combustion Instability Through a Distributed Flame Response Function

2012 ◽  
Author(s):  
Giovanni Campa ◽  
Sergio Mario Camporeale ◽  
Ezio Cosatto ◽  
Giulio Mori
Keyword(s):  
Time Delay ◽  
Combustion Chamber ◽  
Response Function ◽  
Gas Turbines ◽  
Combustion Instability ◽  
Operating Conditions ◽  
Intensity Coefficient ◽  
Injection Point ◽  
Thermoacoustic Instability ◽  
Flame Response

Modern gas turbines equipped with lean premixed dry low emission combustion systems suffer the problem of thermoacoustic combustion instability. The acoustic characteristics of the combustion chamber and of the burners, as well as the response of the flame to the fluctuations of pressure and equivalence ratio, exert a fundamental influence on the conditions in which the instability may occur. A three dimensional finite element code has been developed in order to solve the Helmholtz equation with a source term that models the heat release fluctuations. The code is able to identify the frequencies at which thermoacoustic instabilities are expected and the growth rate of the pressure oscillations at the onset of instability. The code is able to treat complex geometries such as annular combustion chambers equipped with several burners. The adopted acoustic model is based upon the definition of the Flame Response Function (FRF) to acoustic pressure and velocity fluctuations in the burners. In this paper, data from CFD simulations are used to obtain a distribution of FRF of the κ-τ type as a function of the position within the chamber. The intensity coefficient, κ, is assumed to be proportional to the reaction rate of methane in a two-step mechanism. The time delay τ is estimated on the basis of the trajectories of the fuel particles from the injection point in the burner to the flame front. The paper shows the results obtained from the application of FRF with spatial distributions of both κ and τ. The present paper also shows the comparison between the application of the proposed model for the FRF and the traditional application of the FRF over a concentrated flame in a narrow area at the entrance to the combustion chamber. The distribution of the intensity coefficient and the time delay proves to have an influence, both on the eigenfrequency values and on the growth rates, in several of the examined modes. The proposed method is therefore able to establish a theoretical relation of the characteristics of the flame (depending on the burner geometry and operating conditions) to the onset of the thermoacoustic instability.

Influence of Flame and Burner Transfer Matrix on Thermoacoustic Combustion Instability Modes and Frequencies

2010 ◽  
Author(s):  
Giovanni Campa ◽  
Sergio Mario Camporeale
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
Transfer Matrix ◽  
Acoustic Waves ◽  
Gas Turbines ◽  
Combustion Instability ◽  
Experimental Tests ◽  
Full Scale ◽  
Operating Conditions ◽  
Actual Geometry

The main origin of combustion instability in modern gas turbines is considered to be related to the interaction between acoustic waves and flame perturbations. An important role is played by the characteristics of combustion chamber and burners, because they influence the operating conditions at which the instability may occur. Experimental tests carried out on single burner arrangements fail to give adequate indications for the design of a full scale combustion chamber, due to the interaction of the local flame fluctuations with the propagation of the pressure waves, that have a wavelength of the same order of magnitude of the main dimensions of the chamber. Therefore there is a large interest on developing techniques able to make use of the data gathered from tests carried out on a single burner for predicting the thermoacoustic behavior of the combustion chamber at full scale with its actual geometry. A three dimensional finite element code has been developed for predicting acoustically driven combustion instabilities in combustion systems with complex geometries. The code allows one to identify the frequencies at which thermoacoustic instabilities are expected and the growth rate of the pressure oscillations, at the onset of instability, under the hypothesis of linear behaviour of the acoustic waves. The code permits to represent heat release fluctuations through an n–τ Flame Transfer Function (FTF) model and to adopt the transfer matrix method for modelling the burners. The FTF and the burner transfer matrix (BTM), as well as the temperature field and the flame location, needed for the simulation, can be obtained from experimental tests. Moreover, the code is able to make use of the local distribution of n and τ that can be evaluated from computational fluid dynamic studies on the single burner. The paper shows the importance of the flame characteristics, such as dimensions and shape of the heat release zone and its location within the combustor, underlying their influence on the instability of the modes and so the potential of the proposed method as a design tool for defining the burner characteristics and the acoustic impedance at the boundaries of the combustion chamber.

Experimental Investigations of Pressure Drop in the Combustion Chamber of Gas Turbine

1989 ◽  
Author(s):  
Marek Dzida ◽  
Krzysztof Kosowski
Keyword(s):  
Pressure Drop ◽  
Combustion Chamber ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Relative Pressure ◽  
Wide Range ◽  
Few Data

In bibliography we can find many methods of determining pressure drop in the combustion chambers of gas turbines, but there is only very few data of experimental results. This article presents the experimental investigations of pressure drop in the combustion chamber over a wide range of part-load performances (from minimal power up to take-off power). Our research was carried out on an aircraft gas turbine of small output. The experimental results have proved that relative pressure drop changes with respect to fuel flow over the whole range of operating conditions. The results were then compared with theoretical methods.

Application of Active Combustion Instability Control to a Heavy Duty Gas Turbine

1998 ◽  
Vol 120 (4) ◽  
pp. 721-726 ◽  
Author(s):  
J. R. Seume ◽  
N. Vortmeyer ◽  
W. Krause ◽  
J. Hermann ◽  
C.-C. Hantschk ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Combustion Instability ◽  
Pressure Fluctuations ◽  
Preventive Measure ◽  
Feedback System ◽  
Operating Conditions ◽  
Combustion Instabilities ◽  
Instability Control ◽  
Heavy Duty Gas Turbine

During the prototype shop tests, the Model V84.3A ring combustor gas turbine unexpectedly exhibited a noticeable “humming” caused by self-excited flame vibrations in the combustion chamber for certain operating conditions. The amplitudes of the pressure fluctuations in the combustor were unusually high when compared to the previous experience with silo combustor machines. As part of the optimization program, the humming was investigated and analyzed. To date, combustion instabilities in real, complex combustors cannot be predicted analytically during the design phase. Therefore, and as a preventive measure against future surprises by “humming,” a feedback system was developed which counteracts combustion instabilities by modulation of the fuel flow rate with rapid valves (active instability control, AIC). The AIC achieved a reduction of combustion-induced pressure amplitudes by 86 percent. The Combustion instability in the Model V84.3A gas turbine was eliminated by changes of the combustor design. Therefore, the AIC is not required for the operation of customer gas turbines.

Nonlinear Heat-Release/Acoustic Model for Thermoacoustic Instability in Lean Premixed Combustors

1999 ◽  
Vol 121 (3) ◽  
pp. 415-421 ◽  
Author(s):  
A. A. Peracchio ◽  
W. M. Proscia
Keyword(s):  
Heat Release ◽  
Limit Cycle ◽  
Gas Turbines ◽  
Pressure Fluctuations ◽  
Parametric Model ◽  
Operating Conditions ◽  
Cycle Frequency ◽  
Thermoacoustic Instability ◽  
Lean Premixed ◽  
Industrial Gas Turbines

Lean premixed combustors, such as those used in industrial gas turbines to achieve low emissions, are often susceptible to the thermoacoustic combustion instabilities, which manifest themselves as pressure and heat release oscillations in the combustor. These oscillations can result in increased noise and decreased durability due to vibration and flame motion. A physically based nonlinear parametric model has been developed that captures this instability. It describes the coupling of combustor acoustics with the rate of heat release. The model represents this coupling by accounting for the effect of acoustic pressure fluctuations on the varying fuel/air ratio being delivered to the flame, causing a fluctuating heat release due to both fuel air ratio variations and flame front oscillations. If the phasing of the fluctuating heat release and pressure are proper, an instability results that grows into a limit cycle. The nonlinear nature of the model predicts the onset of the instability and additionally captures the resulting limit cycle. Tests of a lean premixed nozzle run at engine scale and engine operating conditions in the UTRC single nozzle rig, conducted under DARPA contract, exhibited instabilities. Parameters from the model were adjusted so that analytical results were consistent with relevant experimental data from this test. The parametric model captures the limit cycle behavior over a range of mean fuel air ratios, showing the instability amplitude (pressure and heat release) to increase and limit cycle frequency to decrease as mean fuel air ratio is reduced.

An Investigation of Turbine Erosion by Combustor Generated Carbon in a Light Weight Marine Gas Turbine

1978 ◽  
Author(s):  
R. J. Russell ◽  
J. J. Witton
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Fuel Type ◽  
Test Rig ◽  
Erosion Process ◽  
Marine Application ◽  
Mineral Dusts

A study has been made of the turbine erosion problem encountered in a marinized aero gas turbine which arose from the change of fuel type necessitated by the marine application. The work has involved the development of a technique for collecting carbon shed from the combustion chamber under engine operating conditions. Tests using the collector were made with a single combustor test rig and compared to engine experience. Combustion chamber modifications were developed having low solids emissions and their emissions characterized using the collector. The data from the collector show that smaller particles than hitherto collected can produce significant long-term erosion and that reduction on both size and quantity of particles is necessary to reduce erosion to acceptable levels. The data obtained in this study are compared with other published information on the basic erosion process and erosion in gas turbines by natural mineral dusts. The implications of the results to current and future engines are discussed.

Adjoint Methods for Elimination of Thermoacoustic Oscillations in a Model Annular Combustor via Small Geometry Modifications

2018 ◽  
Author(s):  
José G. Aguilar ◽  
Matthew P. Juniper
Keyword(s):  
Sensitivity Analysis ◽  
Time Delay ◽  
Heat Release ◽  
Combustion Chamber ◽  
Heat Release Rate ◽  
Release Rate ◽  
Gas Turbines ◽  
Acoustic Pressure ◽  
Annular Combustor ◽  
Thermoacoustic Oscillations

In gas turbines, thermoacoustic oscillations grow if moments of high fluctuating heat release rate coincide with moments of high acoustic pressure. The phase between the heat release rate and the acoustic pressure depends strongly on the flame behaviour (specifically the time delay) and on the acoustic period. This makes the growth rate of thermoacoustic oscillations exceedingly sensitive to small changes in the acoustic boundary conditions, geometry changes, and the flame time delay. In this paper, adjoint-based sensitivity analysis is applied to a thermoacoustic network model of an annular combustor. This reveals how each eigenvalue is affected by every parameter of the system. This information is combined with an optimization algorithm in order to stabilize all thermoacoustic modes of the combustor by making only small changes to the geometry. The final configuration has a larger plenum area, a smaller premix duct area and a larger combustion chamber volume. All changes are less than 6% of the original values. The technique is readily scalable to more complex models and geometries and the inclusion of further constraints, such that the combustion chamber itself should not change. This demonstrates why adjoint-based sensitivity analysis and optimization could become an indispensible tool for the design of thermoacoustically-stable combustors.

Validation of a Novel LES Approach Using Tabulated Chemistry for Thermoacoustic Instability Prediction in Gas Turbines

2015 ◽  
Author(s):  
Stefan Dederichs ◽  
Nikolaos Zarzalis ◽  
Christian Beck
Keyword(s):  
Gas Turbines ◽  
Mixture Fraction ◽  
Propagation Speed ◽  
Co2 Concentration ◽  
Operating Conditions ◽  
Combustion Model ◽  
Scattering Method ◽  
Thermoacoustic Instability ◽  
Tabulated Chemistry ◽  
Premixed Laminar

For the prediction of thermoacoustic instabilities in gas turbines, a compressible, unsteady LES approach was validated for 1D, lab-scale and technical-scale test cases. The simulations were performed with a novel combustion model, which relies on a combination of tabulated chemistry and flame thickening. A 1D case was used for fundamental verification and to quantify the mesh resolution dependent error. The verification demonstrated sufficiently accurate predictions. In a second step an elevated pressure lab-scale flame was considered to calibrate the model parameter of the turbulence chemistry interaction at relevant conditions. For this case CO2 field data measured with the Raman scattering method is available. Finally, a test rig configuration of a can type combustor was investigated. The comparison between experiment and simulation was performed in terms of thermoacoustic pressure amplitudes at stable and unstable operating conditions. The LES combustion model relies on an artificial thickened flame approach to ensure that the flame propagation speed is reproduced with tolerable error. Tabulated chemistry provides the source term for CO2 (governing species) as a function of the mixture fraction and the CO2 concentration based on premixed, laminar flamelets. The model distinguishes between inherent thickening due to sub grid scale turbulence and explicit laminar thickening. This novel thickening approach is presented for the first time. The presented approach was able to predict the thermoacoustic stability behavior of a gas turbine combustion system correctly.

Combination of 1D Code and CFD for Performance Analysis of a Silo Type Gas Turbine Combustor

2010 ◽  
Author(s):  
N. Rasooli ◽  
S. Besharat Shafiei ◽  
H. Khaledi
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Mass Distribution ◽  
Gas Turbines ◽  
Pressure Loss ◽  
Combustion Efficiency ◽  
Operating Conditions ◽  
Empirical Correlations ◽  
Combustion Chambers ◽  
Cfd Simulations

Whereas Gas Turbines are the most important producers of Propulsion and Power in the world and with attention to the importance of combustion chamber as one of the three basic components of Gas Turbine, various activities in different levels have been done on this component. Because of the environmental limitations and laws related to the pollutants such as NOx and CO, Lean Premixed Combustion Chambers are specially considered in gas turbine industries. This study is part of a Multi-Layer simulation of the whole gas turbine cycle in MPG Company. In this work, the combination of a general 1D code and CFD is used for deriving appropriate performance curves for a 1D and 0D gas turbine design, off-design and dynamic cycle code. This 1D code is a general code which has been developed for different combustion chambers; annular, can-annular, can type and silo type combustion chambers. The purpose of generating this 1D code is the possibility of fast analysis of combustors in different operating conditions and reaching required outputs. This 1D code is a part of a general simulation 1D code for gas turbine and was used for a silo type combustor performance prediction. This code generates required quantities such as pressure loss, exit temperature, liner temperature and mass distribution through the combustion chamber. Mass distribution and pressure loss are analyzed and determined with an electrical analogy. Results derived from 1D code are validated with empirical data available for different combustors. There is appropriate agreement between these experimental and analytical results. Drag coefficients for liner holes are available from experimental data and for burner are calculated as a curve with CFD simulations. What differs this code from other 1D codes for gas turbine combustors is the advantage of using combustion efficiencies evolved from numerical simulation results in different loads. These efficiencies are determined with CFD simulations and are available as maps and inserted into the gas temperature calculation algorithm of 1D code. In other 1D codes in this field, empirical correlations are used for combustion efficiency determination. Combustion efficiency curves for design and off-design conditions in this study are achieved by 2D and 3D simulation of combustion chamber with application of EBU/Finite Rate model and 8 step reactions of CH4 burning. Diffusion flame in low loads and premixed flame in high loads are considered. Flame stability and Lean Blow Out charts are evolved from CFD simulation and Heat transfer is applied with empirical correlations.

Thermo-Acoustic Instability Simulation in Gas Turbine

2009 ◽  
Vol 25 (4) ◽  
pp. 433-440 ◽  
Author(s):  
N. Akbari ◽  
N. S. Mehdizadeh
Keyword(s):  
Combustion Chamber ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Combustion Instability ◽  
Longitudinal Mode ◽  
Mixed Gas ◽  
Acoustic Instability ◽  
Longitudinal Modes ◽  
Excitation Probability ◽  
Good Agreement

ABSTRACTThe main aims of this research are, at first, combustion instability study based on equivalence ratio oscillation, and, secondly, investigation various frequency modes of combustion instability, taking combustion chamber geometry into account. Considering the configuration of the simulated combustion chamber, excitation probability of the longitudinal modes is higher than that of transversal modes. The reason of this fact is that the resonance frequency values of the longitudinal modes are less than those of transversal modes. So, the most important frequency mode, during combustion instability, is the first longitudinal mode. In this paper thermo-acoustic instability model is utilized for pre-mixed gas turbines combustion chamber, founded on equivalence ratio oscillation. For this purpose Lieuwen method is developed in order to attain the phase difference between pressure and heat release oscillations. Results concluded from combustion instability simulation for the first longitudinal mode, considering its importance, are compared with experimental data and good agreement is observed.

Modelling of the Combustion Process of a Premixed DLE Gas Turbine

2000 ◽  
Author(s):  
R. L. G. M. Eggels
Keyword(s):  
Reaction Mechanism ◽  
Flow Field ◽  
Combustion Chamber ◽  
Gas Turbine ◽  
Reaction Mechanisms ◽  
Gas Turbines ◽  
Combustion Process ◽  
Operating Conditions ◽  
Dimensional Manifold ◽  
Global Reaction

To obtain a better understanding of the internal combustion processes of gas turbines, CFD computations of a combustion chamber, based on a Rolls-Royce industrial gas turbine, were performed. Minor simplifications are made to generate a 3-D rotational symmetric geometry. Computations are performed at typical gas turbine conditions and natural gas is used as the fuel. An internal Rolls-Royce CFD code is applied to perform the computations. This paper explains the models used for the CFD computations and describes the advantages and limitations on the applied models. The combustion process has been modelled using a two-step global reaction mechanism and Intrinsic Low Dimensional Manifold (ILDM) reduced reaction mechanisms. The global reaction mechanisms are optimised for the considered operating conditions by modification of the reaction rates so that the same burning velocity and the amplitude CO-peak are obtained as predicted by detailed reaction mechanism (GRI 2.11, Bowman 1995). This optimisation is done considering a one-dimensional laminar flame. Although the global reaction mechanism is optimised for one particular operating condition, it appears that it is suitable for use over the entire range of operating conditions. The ILDM reduced reaction mechanisms are derived from GRI 2.11. Two ILDM tables are used to model two operating conditions, as they are specific for the pressure and inlet temperature. The interaction between turbulence and chemistry is modelled using presumed Probability Density Functions (PDF). The flow field in the combustion chamber is studied at isothermal and combusting conditions. It appeared that the flow field for burning and non-burning circumstances is quite different. There is a lack of experimental data so that it is not possible to verify the CFD results in detail. However, there is knowledge about the mechanisms by which the flame is stabilised and emissions are measured in the exhaust. The predicted flame front position agrees with that which is experimentally observed. The predicted increase of CO at low power is at the same order of magnitude as the measured emissions.

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