Acoustic structure and damping estimation of a cylindrical rocket chamber during oscillation

2 Acoustic structure inside a cylindrical rocket chamber is numerically and theoretically investigated, which is the key for determining the damping performance of the whole chamber to measure the combustion instability. When a mean flow is present, the boundary conditions for acoustics are expressed by complex numbers which is called impedance or admittance. It depends on the Mach number of the mean flow, the frequency, the mode of the oscillation and the shape of the inlet (with injectors) and convergent part of a nozzle. In this study the first tangential mode is intensively investigated for some chamber configurations. First the acoustic structure is investigated with and without a mean flow. Then the damping characteristics is estimated numerically and explained from the theoretical point of view. Finally, the intense first tangential pressure oscillation with a mean flow is numerically reproduced and the characteristic features are compared with those without a mean flow.