Inversion of a Capsule Impacting Water: Flip by Resurge Jet

Abstract

A scalemodel bluntcone capsule intended for ocean splashdown was projected into a water pool to evaluate impact loads and postimpact behavior. In a small region of the speed/angle parameter space, the capsule would reproducibly capsize, flipping forward (pitchdown), despite a pitchup motion induced at impact. Inspection of highspeed video shows that the resurging central jet of the impact cavity is responsible. Capsize occurs when this jet is energetic enough (for which we develop a simple criterion), and is timed to lift the trailing edge of the vehicle. The same phenomenon was observed on the Apollo capsules, and may be relevant for lifeboat deployment from ships and offshore platforms.