Abstract:

The CLSVOF model and dynamic adaptive grid were used to numerically simulate the impact-coalescence process of double droplets on the concave-wall in still water. The results indicate that double droplet coalescence behavior occurred during the rolling and sliding process on the concave-wall with the underwater oleophobic materials, the droplet spreading edges contacted and coalescented after impact on the underwater oleophilic surface. The spreading diameter d, the endpoint distance of double droplets on the concave-wall δ, and the maximum spreading factor β were used to classify three liquid bridge forms. For β≤3.1, droplets coaled and formed a single liquid bridge. For β>3.1 and δ/d<3, a hollow ring with high pressure at the inner edge was formed when the right droplet impacted on concave-wall, and double liquid bridges were formed because of the expansion of the oil droplet spreading area. For β>3.1 and δ/d≥3, a single liquid bridge with a hollow ring was formed, but the wetting area fluctuated after coalescence. The single liquid bridge formed by the coalescence of double droplets has a larger dimensionless flow area. The single liquid bridge was more stable than the double liquid bridge. However, double liquid bridge shortened the duration of the impact wall to coalescence. The discoveries provided a useful theory for understanding the collision and coalescence mechanisms of heterogeneous phases near the cyclone wall. The shortcoming of the coalescence theory on discrete phase droplets was supplemented.

Key words: underwater double droplets, concave-wall, CLSVOF, impact wall, coalescence, liquid bridge

摘要：

利用CLSVOF模型和动态自适应网格数值模拟了静水中双油滴撞击凹壁面及聚并过程。结果表明，双油滴撞击水下疏油凹壁面滚动下滑过程中碰撞产生聚并行为，水下亲油表面上双油滴撞壁后铺展边缘接触产生聚并行为。对凹壁面上油滴铺展直径d、近端点距离δ和最大铺展因子β研究表明：β≤3.1聚并形成单液桥；β>3.1，δ/d<3，右侧油滴撞击凹壁面形成空心环，内边缘存在较高压力，导致油滴铺展面积扩张，促使形成双液桥；当β>3.1，δ/d≥3时形成环孔单液桥，但聚并后油滴与凹壁面的润湿面积存在波动。双油滴聚并形成的单液桥无量纲流通面积较大，稳定性优于双液桥，但双液桥缩短了撞壁-聚并的时长。研究可为深入理解旋流器近壁面非均相聚并机理提供理论支持。

关键词: 水下双油滴, 凹壁面, CLSVOF, 撞壁, 聚并, 液桥