Effect of the impact velocity on the jet generation during the droplet impact

At certain droplet impact conditions, a Worthington jet is generated during the impact of a water droplet on a superhydrophobic surface. We visualized the jet generation using a high-speed camera to measure the jet velocity and found that the jet velocity has distinct peaks at certain Weber numbers. Moreover, a careful observation from obliquely vertical angle revealed that the free interface oscillates due to the surface wave generated at the impact of the droplet. While the required time for the jet generation from the impact is independent from the impact velocity, the oscillation frequency was found to be related to the surface wave (i.e., the impact velocity.) We found that these different characteristics results in the difference in the shape of the cavity immediately before the jet generation. Consequently, we found that the peak of the jet velocity corresponds to a phase of the oscillation that reaches the maximum amplitude.