Abstract

The interactions of acoustic waves and thermoviscous fluids in closed cavities lead to some important physical phenomena such as, linear and nonlinear acoustic standing waves, and acoustic streaming which are very important in a wide range of engineering applications. The present dissertation is focused on the detailed investigation of standing wave dynamics in closed cavities. As a part of this research, novel numerical and experimental techniques are developed to analyze different phenomena caused by acoustic-fluid interaction. Using these techniques, the behavior of pressure, acoustic and streaming velocity fields inside the standing wave resonator, as well as the valveless acoustic pump and micropump are investigated. A new sixth-order accurate compact finite difference method for solving the Helmholtz equation with Neumann boundary conditions is developed. This scheme showed a better performance at higher wave numbers than the finite element method. A new fourth-order numerical scheme is also developed for solving highly nonlinear standing wave equations with no restriction on nonlinearity level and type of fluid. For highly nonlinear waves, the simulation results show the presence of a wavefront that travels along the resonator with very high pressure and velocity gradients. The slopes of the traveling velocity and pressure gradients, and the asymmetry in the pressure waveform are higher for CO 2 than those for air. The spatial and temporal variations of the nonlinear pressure and particle velocity fields inside a resonator are experimentally investigated at different frequencies and intensities. The effects of the excitation frequency and displacement on the streaming structure are also studied. It is found that, the classical streaming is not developed for Re s 1 <6.5, and the irregular streaming patterns are observed at Re s 2 >50. Acoustic streaming patterns are also found to be significantly affected by transverse temperature gradient. A valveless acoustic standing wave pump is developed and the velocity fields inside this novel pump are analyzed. It is found that, the net flow rate of the pump increases with an increase in the pressure amplitude. The behavior of a novel acoustic micropump is also studied at a high frequency. The effect of the diffuser geometry on the pump performance is investigated. The results show that the maximum diffuser efficiency is achieved at the diffuser-nozzle element's half-angle of approximately 45°