Microstreaming by ultrasound contrast microbubble between two parallel walls: shear stress and streamlines

TL;DR

This study numerically investigates acoustic microstreaming caused by oscillating ultrasound contrast microbubbles between parallel walls, revealing vortex formation and shear stress variations relevant for biomedical and industrial applications.

Contribution

It introduces a numerical model combining Boundary Element Method and Nyborg theory to analyze microstreaming with viscoelastic microbubble coatings in confined spaces.

Findings

Vortex rings form near the walls during microstreaming.

Increasing the gap size enlarges the vortex ring.

Shear stress decreases as the gap between walls increases.

Abstract

Acoustic microstreaming has several industrial, therapeutic, and biomedical applications - Acoustic cleaning, micromixing, microfluid transport, hemolysis, sonoporation. The acoustic microstreaming due to the oscillation of ultrasound contrast microbubbles in the middle of the gap between two parallel walls is studied numerically. Axisymmetric Boundary Element Method along with theory of Nyborg is applied to study the streaming flow. Viscoelastic model with exponentially varying elasticity is used to simulate microbubble coating. The microstreaming streamlines near the plane walls and the induced shear stress is plotted. The results show the generation of a ring vortex near the walls. By increasing the gap between the walls, the radial size of the vortex ring increases while the microstreaming shear stress decreases.