Secondary bubble entrapment in shallow and deep water

The dynamics of a liquid drop impact on a liquid surface is experimentally studied in shallow and deep water. A novel mechanism of secondary bubble entrapment is observed during cavity collapse. It is found that the mechanism of secondary bubble entrapment differs slightly from the mechanism of primary bubble entrapment (regular entrapment). This is due to an increase in the Weber number and Froude number, which increases the maximum cavity depth and changes the cavity shape. It is also found that the secondary bubble formation is not only dependent on the impact velocity of the drop but also on the drop shape at the time of impact on the liquid surface. Secondary bubble entrapment was observed both in shallow and deep water, but the mechanism of bubble entrapment varies differently in shallow water and deep water. This is due to the effect of reservoir bottom on the flow field around the cavity in shallow water, which is absent in deep water. The secondary bubble entrapment phenomenon occurs for the lowest vertex cone angle of the cavity with a cusp base at the reservoir bottom, and the size of the secondary air bubble is found to be independent of the impact conditions. It is found that the vertex cone angle of the cavity depends on the Bond number, and it increases with increase in the Bond number at a given water depth.