Wake flow-induced acoustic resonance around a long flat plate in a duct

Flows around long thin blunt flat plates generate acoustic resonances when the sound frequency generated by the vortex shedding becomes close to the frequency of the acoustic mode around the plate. After their mutual capturing, the sound intensity strongly increases. To better understand this phenomenon, here we investigate the interaction between flow and flow-induced acoustic resonance around a long flat plate in a duct. Three acoustic resonance modes were observed as the flow velocity was increased. The acoustic resonance behavior is studied as a function of the shapes of the leading and trailing edges (semicircular and square) and the length of the plate (39 ≤ L/d ≤ 71). The Reynolds numbers based on the plate thickness and free-stream flow velocity ranged from 3300 to 21,300. The influence of the leading edge separation bubble and the trailing edge wake flow on the acoustic resonance is scrutinized by examining the velocity profiles, power spectra, and pressure sound level. The nonlinear behavior of the flow components in the wake is shown at monochromatic sound in the resonance regime. The difference in flow conditions around the plate for the diverse shapes of leading and trailing edges leads to the different efficiency of the sound-flow interaction, which originates the different sound level. It was found that the configuration with a semicircular leading edge and a semicircular trailing edge is the best one for generating aeroacoustic resonance. Possible physical explanations are proposed.