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.

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.

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.

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.

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.

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