THE VORTEX RING VELOCITY RESULTING FROM AN IMPACTING WATER DROP

Experimental observations are reported on the evolution of a vortex ri ng for the first 70 ms after it is created by the impact of a dyed wat er drop upon a pool of clear water. The 2.6 mm diameter drops were rel eased from two heights. The drops impacted the pool with Weber numbers of 23.2 and 16.6 and Froude numbers of 25.2 and 18.0. The Reynolds nu mber of the resulting relaminarized vortex rings based on their diamet er was in the range of 320 to 390. Precisely controlled multiple expos ure photographs were used to measure the position and shape of the vor tex ring versus time, and calculate velocity. It is proposed here that the appropriate time scale is the time it takes for the impact crater to reach its maximum depth. Excellent agreement was found when using this scaling to compare both the present data sets and that previously published for a larger drop.