Generation of high-speed liquid jets by high-speed impact of a projectile

Abstract

In generating a pulsed high-speed liquid jet by the impact of a high-speed projectile on a container filled with a liquid, complicated shock wave phenomena subsequently appear. The shock waves affect the liquid jet not only at the earlier stage of its formation but also at the later stage of its propagation. This paper reports results of experiments performed in order to understand the entire process of the generation of a liquid jet. The liquid jet was driven either by the impact of a polyethylene projectile directly on a container which was filled with water and connected to a nozzle or by collision of the projectile with a metal piston which transfers the momentum of the projectile to compress the liquid. The resulting shock wave and liquid jet were observed by double-exposure holographic interferometry. Impact pressures were measured with commercial pressure transducers and also with laboratory-fabricated pressure transducers made from polyvinylidenedifluoride (PVDF) piezo film. Shock waves were emitted in front of the water jet through the liquid/gas interface at the nozzle exit whether the speed of the water jet was supersonic or subsonic in terms of the speed of sound in air. This transmission process of the shock wave was demonstrated in an experiment in which an underwater micro explosion was carried out just below the air/water interface. A numerical simulation was conducted to understand the nozzle flow and the pressure history in the nozzle.