Reconfigurable phased array ultrasound acoustic streaming actuator for separated wake and turbulent boundary layer manipulation

We investigate the feasibility of a reconfigurable phased array ultrasound acoustic streaming actuator for flow control in two canonical configurations: a circular cylinder wake and a turbulent boundary layer with a wall-mounted actuator. An airborne ultrasonic phased array (AUTD3) is operated to synthesize multiple sound-field topologies, including focused, Bessel, and in-phase (quasi-plane-wave) conditions, and the resulting time-averaged flows are quantified using particle image velocimetry measurements. In the cylinder wake, the actuation modifies both the mean flow organization and the fluctuation statistics, with the outcome strongly dependent on the imposed sound-field topology and the relative strength of the induced motion compared with the freestream. In the turbulent boundary layer, in-phase actuation induces a coherent mean wall-normal response with a spatially periodic structure that is absent without emission. The turbulence statistics exhibit non-monotonic wall-normal variation, indicating that the imposed acoustic field can modify the measured turbulence statistics depending on the distance from the wall. Overall, the results provide an experimental basis for phased array acoustic streaming as a wall-mounted, electronically programmable actuator that can generate reconfigurable forcing fields and induce measurable modifications in separated wakes and wall turbulence.