Vortex shedding induced sound inside a cold-flow simulation of segmented chamber

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