Experimental investigation on vortex sound interaction in self-induced acoustic resonance

Acoustic resonance induced by vortex sound interaction in a confined space could cause both noise pollution and acoustic fatigue issues. The mechanism of vortex sound interaction, especially the acoustic feedback effect on vortex shedding, is a challenging question. External sound excitation method is commonly used in the existing studies, which is straightforward to show the modulate effect of sound on flow field, but would inevitably destroy the inherent coupling process between vortex and sound. In response to this problem, we perform experimental investigation based on a spontaneous resonance system consisting of a flow duct containing a plate. The acoustic feedback effect is evaluated by simultaneously monitoring the sound pressure on the duct wall and the vortex shedding fluctuation velocity behind the plate. By slowly increasing the incoming flow velocity, the frequency lock-in phenomenon is obviously detected. In accordance with our previous prediction, two sub-regions are observed in the lock-in region, which validates the rationality of the frequency competition mechanism during vortex sound interaction. Based on these findings, we propose an acoustic resonance suppression method based on the concept of duct wall treatment. Through introducing a non-locally reacting liner on the duct wall, the lock-in region disappears. Besides, the resonant amplitude of sound pressure and the corresponding fluctuation velocity are greatly reduced, which provides a potential effective control strategy for both the noise and structural vibration caused by acoustic resonance.