Vortex Shedding Induced Sound Inside a Cold-Flow Simulation of Segmented Chamber

Abstract

Results are presented from a cold-ow investigation of acoustic responses driven by ow through two annular baf es in a cylindrical cavity, having (approximately) closed-closed end conditions. The interaction of the ow with cavity acoustic resonances was examined for different baf e radii, positions, spacings, and stiffness. Nominal vortex shedding frequencies were found to depend on baf e spacing and radii ( ow velocity), with little sensitivity to baf e stiffness. Vortex shedding lock-in frequencies were very sensitive to acoustic pressures and/or acoustic particle velocities acting on the ow at both the upstream and downstream baf es. Vortex shedding lock-in occurred in conjunctionwith acoustic standing waves formed between the baf es and ends of the test chamber such that either acoustic pressure maxima (closed conditions) occurred at the upstream baf e or acoustic velocity maxima (pressure release or open conditions) occurred at the downstream baf e. High acoustic pressure at the upstream baf e appeared to enhance the strength of the shed vortices, and low acoustic pressure (high acoustic particle velocity) at the downstream baf e appeared to enhance the strength of the acoustic eld radiated on vortex impingement. For most of the two baf e geometries, baf e-to-nozzle acoustic modes were the dominant mechanism responsible for lock-in and strong reinforcement of vortex shedding driven acoustic excitation.