High-speed jet formation after solid object impact

A circular disc impacting on a water surface creates a remarkably vigorous jet. Here we study this phenomenon in a controlled way by pulling the disc through the free surface at constant speed. An axisymmetric air-filled cavity is formed which eventually pinches off in a single point. Immediately after cavity closure the pinch-off location turns into a stagnation point and the flow pattern changes from radial sink flow into hyperbolic flow. The stagnation point deflects the incoming liquid leading to the formation of two fast sharp-pointed jets shooting up- and downwards from the closure point. We study the jet characteristics as a function of both impact velocity and disc radius.