Numerical Simulation On Nonlinear Acoustic Streaming Boundary Layer Flow In Microfluidics Devices Driven Via Ultrasonic

The technology about microfluidics manipulated via acoustics and ultrasonics had developed rapidly in the recent years because of its' unique strengthens and development potential when compared to other general driven methods, like microvalve, electrical drive, magnetic drive, optics etc. The manipulation on microflow induced by the acoustic streaming is the consequence of that the acoustic energy, because of viscous dissipation, transferred into fluids. Besides, the study on the acoustic streaming boundary layer play great roles in understanding the implementation mechanism of acoustic streaming effects and the applications of ultrasonic devices because of the surface-dominate effects and viscosity-dominate effects in microsacle flow.In past few years, most of applications of acoustic drive devices were performed experimentally, there were few concentrated on the mechanism of acoustic streaming actuation. In addition of the nonlinear characteristics, the classical approximation theories were not applicable for the accurate analysis of acoustic streaming phenomena. Thus, in this paper, Direct Computational Aeroacoustic(CAA) method, CE/SE(Conservation Element and Solution Element) Method, was used to aim at the theoretical study on the microflow driven via bulk acoustic waves. All of the research will provide great improvements on both the theoretical research and the potential applications of acoustic streaming effects. The detailed work including that:1) Validation and verification of CE/SE method by several benchmark problems. When compared to other general CAA methods, CE/SE method have the following significant advantages, including high-resolution, simple mathematical formulation, boundary conditions processing easily and the high adaptabilities to unstructured mesh. 2) Validation and verification of non-reflecting boundary and slip wall conditions. When Knudsen number between 0.01 and 0.1, we need consider the slide effects of the wall boundary conditions. Meanwhile, to avoid the reflection of outgoing sound waves back into the computation domain and thus contaminating the solution, specially developed radiation and outflow or absorbing boundary conditions must be imposed at the artificial exteriorboundaries to assist the waves in exiting smoothly. 3) Research on the structure and flow characteristics of acoustic streaming boundary layer, which induced by the bulk acoustic waves, over a horizontal flat-plate. According to the values of unsteady velocities both in streamwise and perpendicular, vorticity, pressure, density, making an elaborate analysis on the nonlinear multi-layer flow and the energy transformation between inner boundary flow and out boundary flow. Finally, the comparison between different Reynolds numbers had been done. 4) Research on the two dimensional duct acoustic streaming and the microfluidic driven via ultrasonics. A comparison had been implemented concerning how the diameter of the duct and the frequency of wave affect the driven flow under BAWs. Finally, realizing the largest driven efficiency with a best match between these three factors. 5) Research on the implementation mechanism of acoustic streaming effects, represented by the heat and mass transfer on solid-fluid interface. Implementing the numerical simulations on two dimensional parallel flat-plates with a temperature gradient, discussing how the different positions of acoustic actuated devices affect the heat transfer efficiency.