Unsteady Flow Field Simulation of a Single Bubble Rising in Quiescent Water*

The dynamic behavior of a single air bubble rising in quiescent water is investigated numerically at Reynolds number of 1840, Weber number of 6.48 and Eotvos number of 8.5. Both theoretical (Clift, et al. 1978) and experimental (Moreto et al. 2022) studies indicate that the bubble with the aforementioned non-dimensional number values exhibits a wobbling motion during the ascending process. By simulating the instantaneous 3-D flow field around the single rising bubble, the mechanism resulting in the wobbling motion, especially the lateral oscillation of the bubble, is elucidated. The numerical method uses level set phase boundaries immersed in a spatially structured 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 nature of the bubble rising flow, close comparison of the numerical simulation results with the experimental data obtained with Time-Resolved Particle Imaging Velocimetry is implemented, to offer a reliable way of verification and validation of the results.