Suppression of acoustic streaming by the inhomogeneity-induced acoustic body force

Rayleigh streaming in a homogeneous fluid has been extensively studied, and plays an important role in the manipulation of particles in microscale acoustofluidics. In this work, the acoustic streaming is investigated in a glass-silicon microchannel as it evolves in fluids made inhomogeneous in density and compressibility (or speed of sound) by the addition of solute molecules. It is found that the streaming is greatly suppressed in the bulk, due to the competition between the boundary-induced streaming stress and the inhomogeneity-induced acoustic body force. The streaming rolls are initially confined to a narrow region close to the walls, then expand from the walls into the bulk as the inhomogeneity is smeared out by diffusion and advection, and finally the homogeneous state is reached. The efficient suppression of streaming enables manipulation of submicron particles using acoustophoresis.