Wake flow characteristics and unsteady performance of a pump-jet propulsor under hull condition

Abstract

The propulsor is one of the main noise sources of an underwater vehicle. The pump-jet operating under hull condition is in a typical non-uniform strong anisotropic turbulent flow field. In this paper, the wake flow characteristics and unsteady performance of a pump-jet propulsor under hull condition are numerically investigated. RANS method and LES method are used to evaluate and compare the ability of solving vortex structure, pressure distribution and unsteady force. LES method can capture the interaction between different vortex systems, and the vortex shedding process of the stator wake and appendage wake. These lead to that the frequency spectra of fluctuation pressure have peaks in the low frequency range for LES method. For unsteady force spectrum, the frequency of maximum amplitude of a single blade is mainly affected by relative intensities of the stator wake and appendage wake. "Humps" appear near the blade passing frequency and its multiples for unsteady force spectrum of the rotor for LES method. The blade passing frequency in the rotor force spectrum is generated by the phase cancellation between different blades. The completeness of rotor blade phase cancellation is mainly affected by the intensity of the non-stationarity in the flow field. Overall, it is sufficient to clarify the hydrodynamic performance and the characteristics of fluctuation pressure distribution of the pump-jet with RANS method. The LES method is necessary to obtain reasonable transient characteristics of the unsteady force and vortex system interaction for the pump-jet under hull condition.