title: Supersonic air flow due to solid-liquid impact.
abstract: A solid object impacting on liquid creates a liquid jet due to the collapse of the impact cavity. Using visualization experiments with smoke particles and multiscale simulations, we show that in addition, a high-speed air jet is pushed out of the cavity. Despite an impact velocity of only 1 m/s, this air jet attains supersonic speeds already when the cavity is slightly larger than 1 mm in diameter. The structure of the air flow closely resembles that of compressible flow through a nozzle-with the key difference that here the "nozzle" is a liquid cavity shrinking rapidly in time.
authors.affiliation: Department of Applied Physics and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors.forename: Stephan
authors.initials: S
authors.lastname: Gekle
authors.forename: Ivo R
authors.initials: IR
authors.lastname: Peters
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Gordillo
authors.forename: Devaraj
authors.initials: D
authors.lastname: van der Meer
authors.forename: Detlef
authors.initials: D
authors.lastname: Lohse