Effect of Initial Bubble Shape on Dynamics of a Buoyancy-Driven Bubble

Three-dimensional direct numerical simulation on a single bubble rising by buoyancy in viscous liquids was carried out with the level set method.The effect of initial bubble shape on the bubble dynamics was studied numerically with Etvs number Eo=1-103 and Morton number Mo=10-10-102,and the influencing mechanism was explained in detail.The bubble shape and rise velocity predicted by the simulation agree with a well-known bubble regime phase diagram in literature.In addition,a phase map was also established at high Eo to provide quantitative analysis on the transition of final bubble topology from spherical-cap to toroidal bubble.The numerical results show that the final shape and rise velocity are not affected by the initial bubble shape at low Eo(Eo52),while the final bubble state appears to be the spherical-cap and toroidal bubble and is influenced by initial bubble shape at high Eo and low Mo.The bubble is easier to become a toroidal bubble and the temporal fluctuation of bubble rise velocity is stronger when the aspect ratio of the initial bubble is greater.