基于VOF方法的驻留微气泡形状稳定性仿真研究

Simulation research on shape stability of resident microbubbles based on VOF method

亚微米级的驻留微气泡在强剪切流中发生变形,会导致将气泡简化为完全滑移刚性壁面而进行的数值仿真出现明显误差。文中采用了VOF方法求解驻留微气泡的气—液两相流平板Couette流场模型,利用剪切流粘性力与表面张力的比值毛细数Ca作为判据,得到了Ca=0.1作为亚毫米尺度微气泡在剪切流中发生显著变形的临界值,并将Ca<<0.1作为将驻留微气泡简化为完全滑移刚性壁面的适用条件。通过仿真得出滑移长度随毛细数增大而减小,当毛细数超过0.1时,驻留微气泡起到增阻作用。在微气泡不发生严重变形的前提下,选择尽量大尺寸的气泡有利于提高减阻效果。

Deformation of submillimeter resident microbubbles, which caused by strong shear flow, will lead to considerable error in numerical simulation based on a rigid wall premise. In this paper, the VOF（volume of fluid） method is adopted to study resident microbubbles in gas-liquid two phase Couette flow. Capillary number Ca, the ratio of the viscous force in shear flow to surface tension, is regarded as a criterion, and Ca=0.1 is the critical value for submicron resident microbubbles to deform significantly. When Ca〈〈0.1, it is rational to simplifying mircobubles as slip rigid wall. Furthermore, slip length decreases with the increasing of Ca. After Ca is more than 0.1, microbubbles play a part in increasing drag. So, drag reduction will be improved by increasing the dimensions of microbubbles in the circumstances that severe deformation has not occurred.