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 time 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 suggests that the suppression of the wall-normal velocity component is the source of the wall-induced lift force.