Numerical investigation into effects on momentum thrust by nozzle's geometric parameters in water jet propulsion system of autonomous underwater vehicles

Abstract

In the water jet propulsion system of autonomous underwater vehicles (AUVs), the nozzle is an important energy conversion component to generate reaction thrust, which consists of momentum thrust and pressure thrust. This paper presents a numerical investigation into four different nozzles (cos, exponent, cylindrical and conical ones) for the water jet propulsion system of AUVs. The effects of geometric parameters (length L and wall roughness Ks) and dynamic parameter (backpressure with constant pressure difference) of four different nozzles on the momentum thrust, average fluid velocity and vapor mass flow rate are analyzed. The governing equations are solved through computational fluid dynamics (CFD) software Fluent 14.0. The results show that cos nozzle which produces more momentum thrust is the most appropriate, and the nozzle length L is proposed to set 36mm. The effects of wall roughness Ks are different on four nozzles, and the smooth inner wall is proposed for cos nozzles. This study provides instructional principles for the design of nozzle in water jet propulsion system of AUVs.