Influence of asymmetric pre-whirl stator spacing on unsteady characteristics of pump-jet propulsor

This work studies the effect of the asymmetric pre-whirl stator spacing on the hydrodynamic performance of a pump-jet propulsor (PJP). The PJP contains a 13-stator and 7-rotor. The stator count is altered in the upper and lower half, and the total count is held constant. Results show that the steady performance is independent of the stator non-uniformity at design conditions. While the unsteady fluctuation of the rotor force and flow field is deeply affected by this adjustment. The cause is that the different incident angles of each rotor resulted from various stator spacing. The larger the stator count on one side, the great the incident angle in the corresponding location. Eventually, the stator root vortices in the lower half, where stator count is relatively larger, are weakened, whereas the tip vortex shape and intensity are not affected by the stator non-uniformity. Most notably, the PJP with a slight change of stator arrangement, in which the difference between two half parts is one, does not cause a significant change in flow, and the thrust amplitude at specific frequency decreases by 40% compared to the uniform stator case.