Effect of Nozzle Exit Geometry on Submerged Jet Characteristics in Underwater Propulsion

Abstract

The characteristics of combustor operating under submerged conditions are affected by the two phase interaction of exhaust gas jet from the combustor with surrounding water. In the present work five nozzle exit cross-sections (circular, square, triangular and elliptical with aspect ratio of 1.5 and 2.5) are investigated. The combustor exit gases are simulated with air and helium to examine the effect of gas property variation. Sound pressure levels, pressure fluctuations in the combustion chamber and the jet exit signatures with different nozzle geometries and jet momentums are examined. High-speed imaging is used to examine the two-phase region formed by the gas jets in underwater propulsion conditions and the associated instabilities. Dynamic pressure sensor is used to study the effect of submerged jet on the pressure fluctuations in the upstream gas chamber. The sound pressure level from the elliptical geometry is found to be lower than the circular, square and triangular geometries. The frequency of jet instabilities is observed to increase with increase in the jet momentum but independent of nozzle exit cross-section. The pressure fluctuation in the gas chamber is coupled with the instabilities downstream in the two phase region. At lower jet momentum bubbling regime is present but it transitions to more jet like behavior with increase in the jet momentum.