Abstract

The study of acoustic streaming, in which the nonlinear interaction of time-periodic sound waves drives time-mean flows, dates back to the work of Lord Rayleigh. Surprisingly, when an acoustic wave interacts with a thermally stratified fluid, a distinct, much stronger type of streaming can occur. We uncover the physical origin of this strong streaming by analyzing the dynamics induced by a standing acoustic wave in a gas-filled channel with walls maintained at differing temperatures. In contrast with Rayleigh streaming, the emergent mean flow has an amplitude comparable to that of the acoustic wave, leading to two-way coupling between the wave and streaming that we capture using multiscale asymptotic analysis. Although the flow is acoustically-driven and buoyancy forces are not included, the streaming temperature field superficially resembles that arising in Rayleigh-Benard convection. The velocity field differs, however, being strongly confined to the periphery of the convection cells. We elucidate the physical origin of this flow pattern and quantify the forced convective heat transport accomplished by the streaming as a function of the domain aspect ratio.