静止水中单个上升气泡的直接数值模拟

本文发展了基于Front Tracking的直接数值模拟方法研究气液两相界面的迁移特性,该方法对气液两相采用半隐式的分步法直接求解N-S方程,耦合Front Tracking Method获得两相界面的三维变形。针对无边界以及垂直壁面附近静止水中的单个气泡上升过程进行模拟,研究气泡运动的机理以及气泡与壁面的相互作用。数值模拟准确再现了气泡的上升过程和变形,不同Re数下气泡的上升速度计算结果同经验关联式非常吻合,验证了该方法的有效性。随后分析了气泡周围流场的结构,发现壁面对气泡周围流场的抑制是壁面对气泡作用力的主要原因,将导致气泡逐渐偏离垂直壁面。

DIRECT NUMERICAL SIMULATIONS OF A SINGLE BUBBLE RISING IN STILL WATER

Direct numerical simulation based on the front tracking method is developed to investigate the migration characteristics of gas-liquid two-phase flow. Both liquid and gas phases are treated as incompressible fluid, and the finite volume method with the cell-centered primitive variable arrangement is used for the discretization. The tune integration is carried out by the semi-implicit fractional step method. Front-tracking method is used to express the moving interface between bubble and surrounding fluid so as to get the three-dimensional bubble deformation. With this method, a single bubble rising in unbounded/wall-bounded water is conducted in three dimensions to investigate the bubble motion mechanism and the bubble-wall interaction. Deformed bubble shape and the zigzag motion are reproduced under different Reynolds number. The calculated rising velocity agrees quite well with available empirical correlations, which validates the accuracy of this method. The investigation of the velocity field around the bubble suggess that the suppression of the wall-normal velocity component is the source of the wall-induced lift force.