气泡碰壁反弹的动力学模型研究

为了解气泡与壁面相互作用的物理机制和详细动力学过程,对气泡与壁面碰撞反弹的动力学过程进行了分析,综述了理论模型的发展过程,并采用所建立的理论模型进行数值求解.当毫米级气泡以一定速度垂直撞击壁面时,气泡与壁面之间存在一层液膜,该液膜呈现多种形状.气泡的变形会改变薄膜内压强的分布,形成薄膜排水过程.气泡在与壁面作用的过程中会反弹多次直至动能被完全消耗.在建立的动力学模型中,液膜厚度分布由Stokes-Reynolds方程描述,液膜内压强由Young-Laplace方程求得,在气泡的轨迹模型中引入了由液膜内压强引起的壁面诱导力.结果表明:描述液膜厚度及膜内压强的SRYL模型能够捕捉薄膜变化的动力学行为,基于薄膜润滑近似的壁面诱导力模型可以较好地预测气泡多次反弹的运动轨迹,壁面诱导力在气泡撞击壁面的过程中对气泡运动起主导作用;随着气泡尺寸和雷诺数的增大,气泡的反弹次数会逐渐增加,气泡是否反弹以及反弹次数与雷诺数有着直接的关系.

Study of Dynamic Model for Bubble Impact and Bounce from Rigid Wall

In order to understand the physical mechanism and detailed hydrodynamic process of the interaction between bubble and rigid wall, the dynamic process of the interaction between bubble and wall was analyzed and the development of theoretical model was summarized. The numerical solution was carried out by using the theoretical model established. When a bubble on millimeter size range collided with a rigid wall vertically, a liquid film was formed between the wall and the bubble surface. The abundant and complicated film appeared in different forms. Deformation of the bubble surface would change the distribution of pressure in the film and the film drainage process occurred. The bubble rebounded several times in the process of interaction with the wall until the kinetic energy was completely dissipated. In the dynamic model established, the film thickness was described by Stokes-Reynolds equation and the pressure distribution in the liquid film was calculated by Young-Laplace equation. The wall-induced force caused by pressure was introduced into the trajectory model of bubble. The results show that the wall induced force model based on the thin film lubrication approximation can predict the trajectory of bubbles with good accuracy and reflect the dynamic process of multiple rebounds of bubbles very well. The wall induced force plays a dominant role in the bubble motion in the process of collision. With the increase of bubble size and Reynolds number, the number of bubble rebounds will increase gradually. Whether bubble rebound or not and the number of rebounds are directly related to Reynolds number.