Acoustic Streaming near a Boundary

An approximate solution is developed for sonically‐induced steady flow near a fluid‐solid interface. The result is valid, subject to stated conditions, for the flow near any portion of surface in the vicinity of which the irrotational oscillatory velocity distribution ua is known. The principal condition on the validity is that the acoustic boundary layer parameter (ν/ω)12 (where ω is the angular frequency and ν is the kinematic viscosity coefficient for the fluid) should be small compared to the scale of ua. Applications of the general result are made to special situations, one case of particular interest being that of a small source near a rigid plane. The conclusion is reached that small compressible bodies, and especially resonant gas bubbles, resting on boundaries, are likely sites of pronounced microstreaming a sound field.