Acoustic streaming induced in focused Gaussian beams

Abstract

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.

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

“…His claim that his results can be used to determine the viscosities of a fluid should be tempered by the observation made by Lighthill (1978) that other forms of dissipation, scattering, thermal, etc., are also likely to be significant and cause an error in this estimate. Later analyses by Kamakura et al (1995) and others have taken into account more realistic acoustic intensity distributions, Gaussian, for example, and nonlinearity of the acoustic wave due to the convective acceleration by relaxing the one-dimensional assumption (Rudenko and Soluíàn, 1977).…”

The vortex flow caused by sound in a bubbly liquid

“…(27), which is described by the term ( · ∇) Ω. It is well established that accounting for this term prevents enlargement of vorticity with time [21]. Numerical results show impact of non-linearity, dispersion, and diffraction of an acoustic beam on the vortex motion.…”

Effects of acoustic nonlinearity and blood flow cooling during HIFU treatment

“…The heat sink has association with the hydrodynamic equations. The vector equation for modeling blood flow motion, subject to the divergence free constraint equation 0 u , in the presence of acoustic stress is as follows [6] …”

“…To retain the prediction accuracy at a lower computational cost, we are motivated to develop a scheme that can give us the accuracy order of sixth in a grid stencil involving only three points. To achieve the above goal, we define firstly the values of (2) u s , (4) u t and (6) u w at a nodal point j. Development of the compact scheme at j x is to relate t , s and w with u as follows:…”