Numerical Design Study of Duct and Stator for a Pump-Jet Propulsor

The pump-jet propulsor consists of a duct, a rotor and stators which are installed upstream of the rotor to provide pre-swirl flow or downstream of rotor to absorb the kinetic energy in the flow. The strong interactions between the three components and the vehicle are closely related to their design and exert great effect on noise and hydrodynamic performance. This paper attempts to develop an effective and efficient method for the optimal design of the duct and the pre-swirl stators under the influence of vehicle and rotor via viscous flow CFD simulations. In this paper, the two key parameters, attack angle of the duct and pitch angle of pre-swirl stators, are investigated. The numerical simulations are based on the solution of the Reynolds-Averaged Navier-Stokes (RANS) equations using a two-layer realizable k-ε model for turbulence closure. The computational domain is discretized into mixed unstructured cells. The software package STAR-CCM+ is used for both grid generations and flow simulations. The rotor is replaced by the body-force model which is proposed according to the load distribution of the rotor in pump-jet propulsor. Total thrust of body force balances the resistance of a fully-appended underwater vehicle and its propulsor in the self-propulsion simulations and torque is determined by assuming that the propulsive efficiency is 80%. To the end of the optimal design, the total resistance, as the main consideration, and detailed flow field, such as pressure distribution, are numerically investigated for varied attack angles of the duct and pitch angles of pre-swirl stator. It is shown that the two parameters have significant impact on the performance of the propulsor and the recommended design is given.