A Numerical Analysis and Measurements of Acoustic Streaming

Acoustic streaming induced by a focused sound source is investigated numerically and experimentally. Two dimensional Navier-Stokes equation in cylindrical coordinates system is solved numercally under the external force field derived from the sound pressure fields. The sound pressure fields are calculated for a focused sound source with uniform pistonlike oscillation or Gaussian profile oscillation by using Rayleigh\u27s equation neglecting the acoustic nonlinearity and absorption. Two dimensional sound pressure and streaming velocity ditributions are measured in pure water using 6MHz focused sound source with 19mm in diameter and about 120mm in focal length. Numerical results for sound pressure and streaming velocity are in good agreement with those measured. It is confirmed that the acoustic streaming induced by the external force is proportional to both sound intensity and absorption. In the present case where the ultrasound intensity is relatively small, the acoustic nonlinearity is found to be not significant