Schlichting and Rayleigh Streamings within a parallel-plate structure in thermoacoustics with wall vibration

This study numerically investigates the phenomenon of acoustic streaming based on a standing-wave thermoacoustic test rig with structural vibration, operating at a flow frequency of 23.6 Hz and a parallel-plate stack with isothermal conditions. Using a validated two-dimensional CFD model, the research explores the streaming patterns at the drive ratio of 3.01% for a system that operated with either air or helium as the working fluid in the absence of thermal gradients. The findings reveal that Rayleigh streaming becomes increasingly dominant in the free-stream regions of oscillatory flow, while Schlichting streaming intensifies velocity within the boundary layers, thereby contributing to complex flow interactions, especially in cases with air as the working fluid. Vorticity visualizations and velocity profile analyses confirm the presence of acoustic streaming superimposed on the primary oscillatory flow, with significant streaming intensity for the system operated with air, while vortex structures become more pronounced when the system is operated with helium. Overall, the study clarified the coupled effects of boundary-layer and bulk-flow streaming mechanisms for future consideration in evaluating flow dynamics in thermoacoustic devices.