Numerical and experimental investigations of the acoustic standing wave resonator, pump, and micropump
Numerical and experimental investigations of the acoustic standing wave resonator, pump, and micropump
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发表时间：
2008
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通讯作者：
M. Nabavi
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作者：
M. Nabavi
封闭腔体中声波与热粘性流体的相互作用导致了一些重要的物理现象，如线性和非线性声驻波、声流等，这些现象在工程应用中具有重要意义。本论文主要研究封闭腔体中的驻波动力学。作为这项研究的一部分，新的数值和实验技术的开发，以分析不同的现象所造成的声流体相互作用。利用这些技术，研究了驻波谐振腔以及无阀声泵和微泵内部的压力场、声场和流速场的特性。提出了一种新的求解Helmholtz方程Neumann边界条件的六阶精度紧致差分方法。该方法在高波数时比有限元方法具有更好的性能。本文还发展了一种新的四阶数值格式，用于求解高度非线性的驻波方程，对流体的非线性程度和类型没有任何限制。对于高度非线性的波，模拟结果显示存在一个波前，该波前沿着谐振器以非常高的压力和速度梯度传播。CO2气体的速度梯度和压力梯度的斜率以及压力波形的不对称性均大于空气。实验研究了不同频率和强度下谐振腔内非线性压力场和粒子速度场的时空变化。研究了激励频率和位移对流动结构的影响。结果发现，经典的流是不发达的Re s 1 50。声流模式也被发现是显着的横向温度梯度的影响。研制了一种无阀声驻波泵，并对该泵内部的速度场进行了分析。结果表明，泵的净流量随压力幅值的增大而增大。研究了一种新型声学微泵的高频特性。研究了扩压器几何形状对泵性能的影响。结果表明，扩压器-喷管元件的半锥角约为45°时，扩压器效率最大
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 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°