Development of an ultrasound acoustic streaming actuator for flow control

The present study aims to develop an ultrasound acoustic streaming actuator for flow control. The driving force can be derived from the continuity equation and the Navier-Stokes equation for the viscous compressible flow. Commercially available transducers are used as an ultra sound source, and the acoustic and induced flow characteristics for a single and multiple transducer configurations are examined. The sound pressure distribution indicates the strong acoustic pressure fluctuation near the transducer. For the multiple transducer cases, the region of the strong pressure fluctuation is widened due to the superposition of the waves. The distributions of the induced velocity are evaluated using particle image velocimetry. It is revealed that the maximum flow velocity is about 0.04 m/s for the single transducer case, and the maximum velocity is observed slightly downstream of the high sound intensity region. Since the driving force is proportional to the square of the sound pressure intensity, the higher flow velocity can be achieved using more transducers. A transducer array having 100 transducers has been applied in a turbulent boundary layer. It is confirmed that the flow velocity near the wall increases in the case with the control, and turbulence intensity augments by approximately 17% compared with the case without the control.