Browsing by Author "Reichling, Gilles"

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Open Access
Development of numerical methods for the calculation of thermo-acoustic interactions in gas turbine combustion chambers
(2015) Reichling, Gilles; Aigner, Manfred (Prof. Dr.-Ing.)
The occurrence of thermo-acoustic instabilities in gas tubine combustion chambers can cause mechanical damage to the combustor system, up to the point of mechanical failure. This work aims to enable the calculation of thermo-acoustic interactions in gas turbine combustor systems through the development of a numerical scheme capable of computing time-dependent compressible reactive flows. Besides Mach numbers close to the subsonic limit, they may become very small in regions with high temperatures and low velocities. The created numerical scheme thus needs to cope with flows close to the subsonic, as well as incompressible limit. The application of the developed numerical method onto gas turbine combustors creates the possibility of capturing thermo-acoustic interaction mechanisms in application-related combustor systems. This aspect fulfills the need to gather more information on thermo-acoustic interaction phenomena and the detailed physical mechanisms that influence their rise towards thermo-acoustic instabilities. For this purpose, a novel projection-based numerical method able to compute compressible reactive flows referred to as the CPM (Compressible Projection Method) method has been developed within this work. It is based on a generic form of the Helmholtz decomposition derived within the frame of this work, leading to a fractional step scheme which solves a predictor and a corrector step. The Poisson equation solved for the pressure within the IPM (Incompressible Projection Method) solution strategy is extended to a Helmholtz equation for the computation of compressible flows. Thus, the CPM method can be seen as an extension of the IPM method towards the regime of compressible flows. Applying the predictor and corrector steps to the conservation equations of the enthalpy and species including Dalton’s law, mixing and combustion phenomena can be included into the computation process, thus enabling the calculation of reactive flows. Since no iterations of the solution process need to be performed, the CPM method describes a highly efficient numerical scheme for the numerical computation of compressible reactive flows. Accurate boundary conditions have been adopted based on a characteristic analysis of the governing flow equations. The characteristic boundary condictions have been implemented and verified by means of an analytical approach providing the response of generated acoustic waves at the in- and outflow boundaries of a one-dimensional rectangular duct. Verification and validation of the numerical method is conducted by one- and two-dimensional test cases. These take flows nearby the incompressible limit, as well as effects of higher Mach numbers into account. As an application-related and validation test case, the three-dimensional turbulent transient flow in a double-swirled gas turbine combustor has been calculated.