Smashed into vapor, cavitation from water slamming

Cliff diving can really hurt. The pain stems from the high pressure generated at impact, which von Karman showed approaches infinity when striking flat (von Karman, 1929).  Yet in contrast to the high pressures found from hard experience we show that a cylinder impacting on a water surface can decrease the local pressure enough to cavitate the liquid in the very early moments (~100 μs).  The liquid cavitates because its slight compressibility allows large pressure waves to form that reflect and create negative pressure regions.  Impact velocities as low as ~3 m/s suffice to cavitate the liquid.  We formulate a new cavitation number to predict the onset of cavitation in these low-speed water slamming scenarios.  These findings imply that cavitation is possible in a variety of free-surface impacts such as boats slamming, cliff diving, and ocean landing of spacecraft.