Acoustofluidic Suppression of Rayleigh Taylor Instability and Fluid Mixing: Stabilization of Stratified Fluids in a Minichannel

Abstract

Rayleigh-Taylor Instability (RTI) typically arises when a dense fluid is superimposed on a lighter fluid, where the desta- bilizing gravitational force acting on miscible fluids drives chaotic mixing. We theoretically present an acoustofluidic method utilizing standing bulk acoustic waves (BAW) to counteract RTI and suppress the mixing of fluids. To success- fully achieve this suppression, we demonstrate that two concurrent conditions are to be satisfied: the acoustic energy density (Eac) of the standing waves must exceed its critical threshold (Ecr), and the orientation of the acoustic waves must be perpendicular to the fluid-fluid interface. This acoustofluidic mechanism reduces the mixing index (MI) by up to an order of magnitude compared to the mixing induced solely by gravity. By analyzing the interplay between acoustic and gravitational forces, this study provides a comprehensive understanding of acoustically modulated mixing dynamics in minichannels.