Simulation and control of instationary reactive flows in matrix burner for small power gas turbine applications

The main objective of this thesis is to analyze combustion instabilities in a matrix burner. The various tools that exist for analyzing thermoacoustic instabilities are applied to the matrix burner with multiple flames. The principal goals are to determine the primary causes of combustion instabilities in the burner and to explore ways of controlling such instabilities in order to prevent damage to the burner. To achieve these goals, the stability map of the burner obtained from measurements is analyzed. This is followed by the analysis of the aerodynamics of the cold flow using CFD. Results obtained from CFD are validated with PIV and LDA results from measurements. Critical are the centerline axial velocity inside the combustion chamber and the recirculation zones on the walls of the combustion chamber and those between the various slots of the matrix burner. Cold flow simulations are followed by reactive flow simulations for both gaseous and liquid fuels. A detailed atomization model is developed for the liquid fuel case from experimental data. Two combustion models, namely, the combined finite rate/eddy dissipation model and the finite rate chemistry model are compared in the CFD simulations of combustion instabilities and validation with measurements are done. The latter is chosen over the former because it accounts for chemistry and it is not numerically dissipative. Two CFD softwares, Fluent and CFX are also compared to determine which is better at capturing acoustics. System identification using CFD is used to determine the flame transfer function and the acoustic transfer matrix. This is followed by the use of acoustic forcing and fuel modulation on the primary and pilot in order to limit the amplitude of the instabilities inside the matrix burner combustor. The 1D acoustic network is used to determine the longitudinal eigenmodes of the matrix burner. This is followed by the use of 3D finite element method (FEM) and fluid-structure interaction (FSI) to determine whether a coupling exist between the fluid and structure of the matrix burner combustor and vice versa. Finally, Full harmonic analysis is performed for the rectangular combustor and the results obtained are validated with analytical results. This is followed by the 3D structure modal analysis of the full matrix burner test rig.