Unsteady Flow Field Simulation of Free Bubble Rising in Quiescent Water

The dynamic behavior of free air bubble rising in quiescent water is investigated numerically at Reynolds number of 1045, Weber number of 3.49 and Eotvos number of 1.77. Both the classic empirical classifications (Clift, et al. 1978) and the new experimental observations (Moreto et al. 2022) indicate that the bubble with the values mentioned above in the non-dimensional parameter space exhibits a wobbling motion during the ascending process. By simulating the instantaneous 3-D flow field around free rising bubbles, the complex mechanism that results in the wobbling motion, especially lateral oscillations, can be better understood. The numerical method uses level set phase boundaries immersed in a spatially structured and normalized grid. The governing equations are discretized using a finite-volume approach. The velocity-pressure coupling is solved using the SIMPLE algorithm. Strong flow quantity variations can be found near the bubble surface and across the vortex rings shed from the bubble in the wake. To handle the challenges posed by the highly unsteady and thin boundary layer that is formed on the bubble surface, highly resolved grids are needed to fully characterize the time-dependent variation of the skin friction force acting upon the rising bubble surfac[XL1] e. Close comparison of the experimental data with the numerical simulations is implemented, to offer a reliable way of verification and validation of both results.*Sponsored by ONR (N00014-21-1-2392)