Influence of the interaction of capillary waves on the dynamics of two drops falling side-by-side on a liquid pool

Abstract

We experimentally examine the coalescence dynamics of two ethanol drops of equal and unequal size, impacting a deep ethanol pool at low impact velocity using a high-speed shadowgraph. By altering the separation distance between the drops and their size ratios, different coalescence outcomes, such as total coalescence, interacting partial coalescence, and non-interacting partial coalescence, have been observed. Two distinct dynamics have been identified, namely, (i) when the primary drops coalesce first before the resulting conglomerate coalesces into the liquid pool and (ii) when the drops coalesce in the liquid pool separately, resulting in capillary waves interaction and affecting the coalescence outcomes. We also observe another fascinating phenomenon for certain parameters as the satellite drops coalesce as they ascend from the liquid pool. It is found that the coalescence time delay between the drops influences the size of the secondary drops by changing the dynamics from the interacting to non-interacting partial coalescence behavior at the coalescence time delay of 1.31. Our results also indicate that when the normalized separation distance between the dispensing needles is greater than 3.2, the capillary waves produced from both the drops do not interact, and the drops exhibit a usual partial coalescence like two single individual drops.