Some thought on the interaction between sound and flow.

Abstract

The glazing flow and the bias flow normally increase the acoustic resistance of perforated plate with back cavity. However, in some conditions, the acoustic resistance decreases and the cavity tone may be occurred. In this paper, several examples concerning on such sound and flow interaction are examined and the mechanism of sound attenuation and sound amplification by sound and flow interaction is discussed. When sound wave impinges on vortices, the sound energy is once transferred to vortex energy and attenuated. The intensified vortex generates new sound. Whether the sound is attenuated or amplified, depends on which is larger, the firstly attenuated sound or secondary generated sound. When the frequency of the impinging sound is close to the frequency of fluid dynamic oscillation, the vortices are easy to move and the acoustic resistance decreases. When the acoustic resistance is negative, the fluid resonant oscillation (cavity tone) is occurred.