Drops settling in sharp stratification with and without Marangoni effects

作者：Blanchette Francois^*; Shapiro Avi M

来源：Physics of Fluids, 2012, 24(4): 042104.

DOI：10.1063/1.4704790

• drops
• flow simulation
• numerical analysis
• solubility
• stratified flow
• surface tension
• suspensions
• two-phase flow

We present numerical simulations of drops settling in a layered ambient fluid. We focus on nearly spherical drops with Reynolds numbers of order 10. The ambient is composed of miscible fluids, with the top layer lighter than the lower one, representing fluid stratified through temperature or salinity variations, while the drop itself is heavier than both layers. The surface tension between the ambient and the drop may or may not be different for each layer. Such a system can be used to model oil droplets settling or rising in the ocean. When surface tension is uniform, the drop slows down significantly as it encounters the transition region, due to entrained fluid from the upper layer, before accelerating again in the lower layer. We characterize this effect in terms of the sharpness of the transition, and the drop's Reynolds number. When the upper and lower surface tensions are not matched, the drop may either suddenly accelerate through the transition region if the lower surface tension is less than the upper one, or be prevented from crossing into the lower layer if the lower surface tension is larger than the upper one. We focus on the drop's speed across the transition, and determine the conditions under which a drop may remain suspended at the transition region.

• 出版日期2012-4