Generation of breathing-like acoustic streaming jet in air by small through-hole in object placed near sound source

When a planar object with a small through-hole at the center was placed near a vibrating surface, a jet flow from the hole was observed. The objective of this study is to clarify the flow velocity distribution and characteristics of the jet phenomenon through measurement and analysis. The airflow with the jet was visualized using particle smoke, a light sheet, and a high-speed camera. The flow velocity fields produced by the jet were calculated by particle image velocimetry. The jet flow from the hole was considered to occur with suction flow around the hole. The maximum velocity of the jet flow was twenty times higher than that of the airflow without the planar object. The sound pressure fields were analyzed by finite element analysis, and high sound pressure was found in the hole. This pressure was higher than that in the air gap between the vibrating surface and the object. Furthermore, it was confirmed that the airflow around the hole fluctuated with driving frequency. Thus, a breathing-like jet was formed in the hole. The flow velocity was increased by increasing the vibration amplitude and decreasing the air gap.