CAA Simulation and Intensity Based Evaluation of a Model Experiment for Indirect Combustion Noise

Abstract

The efficient prediction of combustion noise by a zonal approach is discussed. For the so called propagation zone an optimized finite difference method adopted from fan tone noise propagation is applied together with a linear perturbation approach based on the Euler equations. Special attention is payed to the indirect noise generation in the propagation zone, where initially quiet perturbations of the fluid state radiate noise when accelerated or decelerated in a varying base flow regime. A non-isentropic mathematical model is chosen. The approach is compared with a previously published experiment for the assessment of indirect combustion noise. The numerical results show the strong influence of reflections from the inflow boundary of the plenum on the resulting pressure response in the outlet duct. By assuming reasonable reflections from the plenum, the observed time signal of the pressure reaches a reasonable agreement between numerical simulation and experiment. Furthermore, the acoustic intensity is used to show the good quality of the numerical solution. Finally, the intensity based source location identifies the nozzle as a dominant source of sound, with large magnitudes of generation and annihilation of acoustic energy. The source power found in the heated volume is more than two orders of magnitude smaller than in the nozzle. This result again underlines the importance of indirect combustion noise.