Thermo-acoustic coupling in a differentially heated enclosure: Flow topology bifurcation and heat transfer modulation

This study investigates the complex interplay between standing wave acoustic streaming and natural convection in a differentially heated enclosure via a hybrid lattice Boltzmann method and finite difference solver. Covering Rayleigh numbers from 103 to 105 and various acoustic amplitudes, results reveal a non-monotonic heat transfer modulation driven by the competition between acoustic inertia and thermal buoyancy. In the conduction-dominated regime (Ra = 103), acoustic streaming acts as a powerful mixer, increasing the average Nusselt number by up to 400%. In contrast, the convection-dominated regime (Ra = 105) exhibits a counter-intuitive suppression, where strong acoustic forcing reduces heat transfer efficiency by approximately 41.6%. This suppression arises from antagonistic hydrodynamic interactions, where counter-rotating acoustic vortices disrupt the global buoyancy circulation. Additionally, strong thermo-acoustic coupling at high amplitudes induces a symmetry-breaking bifurcation via baroclinic torque, resulting in a robust asymmetric flow topology. A dimensionless thermo-acoustic velocity ratio is proposed as a unified criterion to predict the enhancement-to-suppression transition, offering key guidelines for acoustic thermal management.