Effects of Blade Number on the Propulsion and Vortical Structures of Pre-Swirl Stator Pump-Jet Propulsors

Reducing the noise of the underwater propulsor is gaining more and more attention in the marine industry. The pump-jet propulsor (PJP) is an extraordinary innovation in marine propulsion applications. This paper inspects the effects of blade number on a pre-swirl stator pump-jet propulsor (PJP) quantitatively and qualitatively. The numerical calculations are conducted by IDDES and ELES, where the ELES is only adopted to capture the vortical structures after refining the mesh. The numerical results show good agreement with the experiment. Detailed discussions of the propulsion, the features of thrust fluctuation in time and frequency domains, and the flow field are involved. Based on the ELES results, the vortices in the PJP flow field and the interactions between the vortices of the stator, rotor, and duct are presented. Results suggest that, though changing the blade number under a constant solidity does not affect the propulsion, it has considerable effects on the thrust fluctuation of PJP. The wakes of the stator and rotor are also notably changed. Increasing the stator blade numbers has significantly weakened the high-intensity vortices in the stator wake and, hence, the interaction with the rotor wake vortices. The hub vortices highly depend upon the wake vortices of the rotor. The hub vortices are considerably broken by upstream wake vortices when the load per rotor blade is high. In summary, the blade number is also vital for the further PJP design, particularly when the main concerns are exciting force and noise performance.

The effect of a plate installation upstream of an orifice on the pressurized flushing efficiency

The effect of a plate installation upstream of an orifice was investigated as a new method for improving the pressurized flushing efficiency. In this regard, a plate with three different widths (B_T) was installed at four different distances (L_T) upstream of the orifice. According to the results, the plate installation significantly increased the pressurized flushing efficiency due to the wake vortices formed upstream of the orifice. The flushing efficiency increased up to a maximum value of 11.5 times relative to what was calculated for the experiment without plate for the same conditions. For the best configuration of the plate width and its distance from the outlet (i.e., L_T/D_O =0.7 and B_T/D_O =0.5, D_O is the orifice diameter), the length, width, and depth of the flushing cone increased by about 160, 90, and 240% relative to the control experiment under the same conditions, respectively.