Acoustic streaming flows in a cavity: An illustration of small-scale inviscid flow

Low Reynolds number flows are typically described by the equations of creeping motion, where viscous forces are dominant. We illustrate using particle image velocimetry (PIV) an example of small-scale boundary driven cavity flows, where forcing relies on viscous mechanisms at the boundary but resulting steady flow patterns are inviscid. Namely, we have investigated acoustic streaming flows inside an elastic spherical cavity. Here, the inviscid equations of fluid motion are not used as an approximation, but rather velocity fields independent of viscosity come as a result from the general solution of the creeping motion equations solved in the region interior to a sphere.