Analytical and Numerical Study of Combustion Noise Through a Subsonic Nozzle

Two mechanisms control sound generated by combustion in gas turbines: direct combustion noise in which acoustic waves generated by the flame propagate from the combustion chamber to the outlet through turbine stages, and indirect combustion noise (or entropy noise) in which entropy waves created by unsteady combustion generate noise as they are accelerated through the turbine stages. These mechanisms can be studied in laboratories by sending acoustic and entropy waves through a nozzle as done in the Entropy Wave Generator experiment. Previous studies have addressed the case where the nozzle is choked and have demonstrated that indirect noise was large compared to direct noise, suggesting that indirect noise only could be retained for gas turbine studies. In the present study, subsonic cases are analysed using, first, a full numerical resolution of the unsteady Euler equations; second, an analytical method based on the work of Marble and Candel in the low-frequency limit, and, finally, the one-dimensional ...