ACOUSTIC STREAMING INDUCED IN FOCUSED GAUSSIAN BEAMS

Axisymmetric flow equations for a viscous incompressible fluid are transformed into the vorticity transport and Poisson's equations. They are numerically solved via a finite difference method imposing appropriate initial and boundary conditions A model source of 1-cm radius and 5-cm focal length with Gaussian amplitude distribution radiates 5-MHz ultrasound beams in water. Numerical examples are shown for buildup of acoustic streaming along and across the acoustic axis. Evidently, hydrodynamic nonlinearity has an essential effect on the streaming generation in comparison with a linear flow case; the nonlinearity reduces the streaming velocity in the focal and prefocal region, whereas it tends to accelerate the flow in the postfocal region. © 1995, Acoustical Society of America. All rights reserved.