Impact of Boundary Conditions on the Reconstructed Flame Transfer Function for Gas Turbine Combustion Systems

2008 ◽  
Author(s):  
Krzysztof Kostrzewa ◽  
Axel Widenhorn ◽  
Berthold Noll ◽  
Manfred Aigner ◽  
Werner Krebs ◽  
...  
Keyword(s):  
Transfer Function ◽  
Boundary Conditions ◽  
Gas Turbine ◽  
Transfer Functions ◽  
Feedback Mechanism ◽  
Pressure Amplitude ◽  
Flame Response ◽  
Gas Turbine Combustion ◽  
Combustion Systems ◽  
The Impact

In order to achieve low levels of pollutants modern gas turbine combustion systems operate in lean and premixed modes. However, under these conditions self-excited combustion oscillations due to a complex feedback mechanism between pressure and heat release fluctuations can be found. These instabilities may lead to uncontrolled high pressure amplitude oscillations which can damage the whole combustor. The flame induced acoustic source terms are still analytically not well described and are a major topic of thermo-acoustic investigations. For the analysis of thermo-acoustic phenomena in gas turbine combustion systems flame transfer functions can be utilized. The purpose of this paper is to introduce and to investigate modeling parameters, which could influence a novel computational approach to reconstruct flame transfer functions known as the CFD/SI method. The flame transfer function estimation is made by application of a system identification method based on Wiener-Hopf formulation. Varying acoustic boundary conditions, combustion models and time resolutions may strongly affect the reconstructed flame response characterizing overall system dynamics. The CFD/SI approach has been applied to a generic gas turbine burner to derive a flame response. 3D unsteady simulations excited with white noise have been performed and the reconstructed flame transfer functions have been validated with experimental data. Moreover, the impact on the reconstructed flame transfer functions because of different boundary condition configurations has been examined.

Validation of Advanced Computational Methods for Determining Flame Transfer Functions in Gas Turbine Combustion Systems

2007 ◽  
Author(s):  
Krzysztof Kostrzewa ◽  
Berthold Noll ◽  
Manfred Aigner ◽  
Joachim Lepers ◽  
Werner Krebs ◽  
...  
Keyword(s):  
System Identification ◽  
Heat Release ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Transfer Functions ◽  
Sound Waves ◽  
Gas Turbine Combustion ◽  
Combustion Systems ◽  
Combustion Processes ◽  
Gas Turbine Burner

The operation envelope of modern gas turbines is affected by thermoacoustically induced combustion oscillations. The understanding and development of active and passive means for their suppression is crucial for the design process and field introduction of new gas turbine combustion systems. Whereas the propagation of acoustic sound waves in gas turbine combustion systems has been well understood, the flame induced acoustic source terms are still a major topic of investigation. The dynamics of combustion processes can be analyzed by means of flame transfer functions which relate heat release fluctuations to velocity fluctuations caused by a flame. The purpose of this paper is to introduce and to validate a novel computational approach to reconstruct flame transfer functions based on unsteady excited RANS simulations and system identification. Resulting time series of velocity and heat release are then used to reconstruct the flame transfer function by application of a system identification method based on Wiener-Hopf formulation. CFD/SI approach has been applied to a typical gas turbine burner. 3D unsteady simulations have been performed and the flame transfer results have been validated by comparison to experimental data. In addition the method has been benchmarked to results obtained from sinusoidal excitations.

Thermoacoustic Analysis of Gas Turbine Combustion Systems Using Unsteady CFD

2005 ◽  
Author(s):  
Bruno Schuermans ◽  
Holger Luebcke ◽  
Denis Bajusz ◽  
Peter Flohr
Keyword(s):  
Transfer Function ◽  
Boundary Conditions ◽  
Gas Turbine ◽  
Network Model ◽  
Full Scale ◽  
Test Facility ◽  
Combustion System ◽  
Acoustic Boundary Conditions ◽  
Gas Turbine Combustion ◽  
Gas Turbine Burner

Unsteady Computational Fluid Dynamics (CFD) has been used to predict thermoacoustic interaction processes in an industrial gas turbine burner. Because detailed unsteady simulation of an entire gas turbine combustion system is forbiddingly expensive, two different approaches have been applied to overcome this problem. In the first approach, time-domain acoustic boundary conditions are applied to the computational domain of the CFD. The idea is to model in CFD only that part of the problem that cannot be represented by low order (acoustic) models. The advantage is not only that the method is much faster; it also allows changes in acoustic boundary conditions without a need to make a new mesh for the problem. This method introduced here is novel and can be used to apply any (causal) acoustic impedance matrix to a CFD computation. The desired impedance can either be obtained analytically, from an acoustic network model or from an acoustic finite element code. The method has been tested on various test cases and proved to be accurate and robust. First, a simple duct with non reactive flow has been simulated. A non refelecting boundary condition for plane waves has been applied. In a further step the methodology was implemented on a gas turbine burner with combustion. The measured acoustic boundary conditions of a single burner test facility have been applied. The predicted pressure spectra are in reasonable agreement with measured pulsation spectra of a full-scale gas turbine burner in an atmospheric combustion test facility. In the second approach a system identification technique is used in a post-processing step of the CFD results. In this way the transfer function relating the acoustic quantities on both sides of the flame is obtained. This transfer function can then be applied to an acoustic network model of the system. The advantage of this method is that once the transfer matrix of the combustion zone is obtained, the influence of combustion system geometry can be investigated in the low order model, which is very fast. This method has been compared with measured transfer matrices of a full-scale swirl stabilized gas turbine burner and proved to be in good agreement.

Accurate Boundary Conditions for the Numerical Simulation of Thermoacoustic Phenomena in Gas-Turbine Combustion Chambers

2006 ◽  
Author(s):  
Axel Widenhorn ◽  
Berthold Noll ◽  
Manfred Aigner
Keyword(s):  
Boundary Conditions ◽  
Gas Turbine ◽  
Simple Algorithm ◽  
Propagation Speed ◽  
Practical Implementation ◽  
Combustion Chambers ◽  
Inhomogeneous Temperature ◽  
Gas Turbine Combustion ◽  
Wave Propagation Speed ◽  
The Impact

The goal of this paper is to discuss the derivation and behaviour of non-reflecting boundary conditions in the framework of accurate calculations of combustion instabilities. Therefore, it is explained for the first time, how to modify the coefficients of the discrete pressure correction equation and of the discrete conservation equations, in order to apply non-reflecting boundary conditions to a pressure based SIMPLE-Algorithm. The theory and practical implementation of the boundary conditions, which are based on Poinsot & Lele’s [1] formulation, will be explained for inflow and outflow boundaries. The method will be validated based upon test cases which are relevant to the simulation of gas turbine combustion chambers. Moreover, the accuracy of non-reflecting boundary conditions is assessed for cases where combustion leads to inhomogeneous temperature and species fields. The impact of the acoustic wave propagation speed on the reflectivity of the non-reflecting boundary conditions is analysed.

Impedance Boundary Conditions for the Numerical Simulation of Gas Turbine Combustion Systems

2008 ◽  
Author(s):  
Axel Widenhorn ◽  
Berthold Noll ◽  
Manfred Aigner
Keyword(s):  
Boundary Conditions ◽  
Gas Turbine ◽  
Acoustic Field ◽  
Time Domain ◽  
Combustion Noise ◽  
Practical Implementation ◽  
Reacting Flow ◽  
Impedance Boundary ◽  
Gas Turbine Combustion ◽  
Combustion Systems

The design process of modern gas turbine combustion systems relies more and more on CFD methods. To capture unsteady combustion phenomena like combustion instabilities or direct combustion noise both the reacting flow field and the acoustic field have to be modeled precisely. To take into account the accurate simulation of the acoustic wave reflection at a boundary condition time-domain impedance formulations have to be used. These conditions allow specifying the frequency depending impedance quantities for example of the fuel line, air supply system, combustion chamber outlet and walls in the time-domain. In the present paper the theory and the practical implementation of the time-discrete impedance formulation are discussed. Here, the link between the time and frequency domain is established by utilizing both the z-transform and Fourier transform. By means of simple test cases the physical effects of acoustically treated boundary conditions on the flow and acoustic field are worked out. Furthermore, the accuracy is analyzed and the need for such boundary conditions in the framework of gas turbine combustion system research and development is discussed.

scholarly journals Comparison of Hydrogen Micromix Flame Transfer Functions Determined Using RANS and LES

2019 ◽  
Author(s):  
Jonathan McClure ◽  
David Abbott ◽  
Parash Agarwal ◽  
Xiaoxiao Sun ◽  
Giulia Babazzi ◽  
...  
Keyword(s):  
Transfer Function ◽  
Transfer Functions ◽  
Diffusion Flames ◽  
Design Tool ◽  
Preliminary Design ◽  
Flame Response ◽  
Combustion Systems ◽  
Acoustic Excitations ◽  
Analytical Expressions

Abstract Hydrogen has been proposed as an alternative fuel to meet long term emissions and sustainability targets, however due to the characteristics of hydrogen significant modifications to the combustion system are required. The micromix concept utilises a large number of miniaturised diffusion flames to improve mixing, removing the potential for local stoichiometric pockets, flash-back and autoignition. No publicly available studies have yet investigated the thermoacoustic stability of these combustion systems, however due to similarities with lean-premixed combustors which have suffered significant thermoacoustic issues, this risk should not be neglected. Two approaches have been investigated for estimating flame response to acoustic excitations of a single hydrogen micromix injector element. The first uses analytical expressions for the flame transfer function with constants obtained from RANS CFD while the second determines the flame transfer function directly using unsteady LES CFD. Results show the typical form of the flame transfer function but suggest micromix combustors may be more susceptible to higher frequency instabilities than conventional combustion systems. Additionally, the flame transfer function estimated using RANS CFD is broadly similar to that of the LES approach, therefore this may be suitable for use as a preliminary design tool due to its relatively low computational expense.

Review of Hybrid Emissions Prediction Tools and Uncertainty Quantification Methods for Gas Turbine Combustion Systems

2017 ◽  
Author(s):  
Sajjad Yousefian ◽  
Gilles Bourque ◽  
Rory F. D. Monaghan
Keyword(s):  
Uncertainty Quantification ◽  
Gas Turbine ◽  
Kinetic Modelling ◽  
Computational Cost ◽  
Chemical Kinetic ◽  
Design Development ◽  
Deterministic Models ◽  
Prediction Tools ◽  
Gas Turbine Combustion ◽  
Combustion Systems

There is a need for fast and reliable emissions prediction tools in the design, development and performance analysis of gas turbine combustion systems to predict emissions such as NOx, CO. Hybrid emissions prediction tools are defined as modelling approaches that (1) use computational fluid dynamics (CFD) or component modelling methods to generate flow field information, and (2) integrate them with detailed chemical kinetic modelling of emissions using chemical reactor network (CRN) techniques. This paper presents a review and comparison of hybrid emissions prediction tools and uncertainty quantification (UQ) methods for gas turbine combustion systems. In the first part of this study, CRN solvers are compared on the bases of some selected attributes which facilitate flexibility of network modelling, implementation of large chemical kinetic mechanisms and automatic construction of CRN. The second part of this study deals with UQ, which is becoming an important aspect of the development and use of computational tools in gas turbine combustion chamber design and analysis. Therefore, the use of UQ technique as part of the generalized modelling approach is important to develop a UQ-enabled hybrid emissions prediction tool. UQ techniques are compared on the bases of the number of evaluations and corresponding computational cost to achieve desired accuracy levels and their ability to treat deterministic models for emissions prediction as black boxes that do not require modifications. Recommendations for the development of UQ-enabled emissions prediction tools are made.

Measurement of Flame Frequency Response Functions Under Exhaust Gas Recirculation Conditions

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Joseph Ranalli ◽  
Don Ferguson
Keyword(s):  
Transfer Function ◽  
Carbon Capture ◽  
Transfer Functions ◽  
Combustion Process ◽  
Exhaust Gas Recirculation ◽  
Exhaust Gas ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Flame Response ◽  
Gas Recirculation

Exhaust gas recirculation has been proposed as a potential strategy for reducing the cost and efficiency penalty associated with postcombustion carbon capture. However, this approach may cause as-yet unresolved effects on the combustion process, including additional potential for the occurrence of thermoacoustic instabilities. Flame dynamics, characterized by the flame transfer function, were measured in traditional swirl stabilized and low-swirl injector combustor configurations, subject to exhaust gas circulation simulated by N2 and CO2 dilution. The flame transfer functions exhibited behavior consistent with a low-pass filter and showed phase dominated by delay. Flame transfer function frequencies were nondimensionalized using Strouhal number to highlight the convective nature of this delay. Dilution was observed to influence the dynamics primarily through its role in changing the size of the flame, indicating that it plays a similar role in determining the dynamics as changes in the equivalence ratio. Notchlike features in the flame transfer function were shown to be related to interference behaviors associated with the convective nature of the flame response. Some similarities between the two stabilization configurations proved limiting and generalization of the physical behaviors will require additional investigation.

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.

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