Thermo-Acoustic Analysis of an Advanced Lean Injection System in a Tubular Combustor Configuration

In this work the thermoacoustic behavior of a tubular combustor has been studied using the acoustic module of the FEM code COMSOL Multiphysics. The performed analysis is based on the resolution of the eigenvalue problem related to an inhomogeneous wave equation which includes a source term representing heat release fluctuations (the so called Flame Transfer Function, FTF) in the flame region. The effect of the mean flow is neglected whereas the effect of temperature variations on pressure waves is included by considering the temperature profile in the combustion chamber obtained from CFD (Computational Fluid Dynamics) computations. Numerical results were compared with both experimental data and results obtained with a monodimensional network-based solver. A criterion to simplify the geometry of a double swirler injector was defined allowing the reduction of the number of elements necessary to model this component. The influence of flame region shape on the eigenfrequencies computation was investigated together with the effect of two different expressions for the flame transfer function. Comparisons with available experimental data showed the necessity of an improved FTF, more suitable for liquid fueled gas turbines where the evaporation process could play an important role in the flame heat release fluctuations.