Acoustic force model for the fluid flow under standing waves

An acoustic Strouhal number is introduced to demonstrate that the viscosity of fluid can be ignored in the process of sound propagation and acoustic streaming is independent on the frequency of the acoustic wave. Furthermore, acoustic force based on the periodic velocity fluctuation caused by standing acoustic wave is introduced into Navier–Stokes equation in order to describe the fluid flow in the acoustic boundary layer. The numerical results show that the predicted results are consistent with the analytic solution. And the effect of the nonlinear terms cannot be ignored so the analytic solution derived by boundary-velocity condition is only an approximation for acoustic streaming.