Acoustic streaming flow driven about and array of sharp-edged obstacles

Abstract

Acoustic streaming is a process that can be used as a flow control mechanism for mixing, sorting, and enhanced transport phenomena. In this work, we present experimental results examining the superposition of acoustic streaming and bulk flow in a microchannel that incorporates an array of sharp-edge obstacles placed uniformly inside the microchannels. In the absence of bulk flow, we perform experiments over a parameter space consisting of obstacle morphology (circle, square, triangle, cross) and input sinusoidal voltage (4–12 V) with a fixed frequency of 5.8 kHz. Microscopic particle image velocimetry (µPIV) measurements yield a velocity range from 37 to 674 µm/s. Importantly, in all shapes, an overall clockwise rotation was found at the right side of the PZT and anticlockwise rotation at the left side of PZT. Although the peak acoustic streaming velocities are different for each shape, we find that the velocity scales nearly quadratically as a function of applied voltage (\({U}_{o}\sim {V}_{\text{app}}^{2}\)), which is consistent with scaling analyses of acoustic streaming in microfluidic systems. A bulk flow of ~ 185 µm/s is imposed on the microchannel at the same time as a 10 V signal. We find that the resulting flow field can be reconstructed by adding the bulk flow field without streaming to the acoustic streaming flow field without bulk flow.