Control of Acoustic Resonance in Shallow Rectangular Cavities Using Surface Mounted Blocks
Flow over rectangular cavities is a potential source of acute noise that poses environmental concerns and structural threats to surrounding components in many engineering applications. In this paper, a passive method for controlling the acoustic resonance resulting from subsonic flows with Mach numbers up to 0.45 over shallow rectangular cavities is investigated. Both experimental and numerical investigations are performed to investigate the effectiveness of attaching blocks of square cross-section in suppressing the flow-excited acoustic resonance in shallow rectangular cavities. Six different square blocks with width to height ratios of w/h = 1, 2, 3, 4, 5, and 6.66 are investigated. The blocks are attached at different locations upstream of the cavity leading edge with d/h = 0, 3, and 6, where d is the upstream distance from the cavity leading edge and h is the block height. The results show that significant attenuation of the generated acoustic pressure with up to 30 dB is achieved using blocks of w/h between 2 and 4. Moreover, it is observed that the most effective attenuation of the acoustic resonance is achieved when the blocks are located at a distance of 3h upstream of the cavity leading edge. Blocks with moderate widths are more effective than blocks that fills the whole width of the wind tunnel. Furthermore, the numerical simulations show that the shape of the blocks initiate vortices of different length and time scales than that of the shear layer over the cavity mouth. The interaction between these vortices and the vortices shed at the cavity leading edge weaken the separated shear layer over the cavity mouth, which, in turn, attenuates the generated acoustic resonance.
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