Characteristics of a Water Jet Driven by Expansion of High-Pressure Bubbles

Abstract

A new type of nozzle generating a two-phase high-speed water jet is presented. The structure is of simple convergent and divergent type. High pressure air is injected into the water flow through thin holes opened downstream of the throat. The increasing ratio of the momentum is higher than 10. As the pressure of the air increases, the speed of the jet increases, but the efficiency decreases. The nozzle with a small opening angle seems to be better, and the holes should be opened near the throat. The speed of the water phase is, in general, higher than that of the air phase. The pressure upstream of the nozzle is not necessarily high, so that this nozzle can work by itself for ship propulsion. The mechanism of generating the water jet is also considered qualitatively.