Wake instabilities of a pre-swirl stator pump-jet propulsor

The wake of a pump-jet propulsor (PJP) with a pre-swirl stator is investigated using stress-blended eddy simulations. The flow field is analyzed in detail through a systematic comparison of the wake morphology under different loading conditions, allowing the destabilization process and the mechanism of wake instabilities to be inspected. To further examine the evolution of the vortices, as well as their interaction and destabilization, the pressure fluctuations and spectra of turbulent kinetic energy are considered. The mean loads are in good agreement with experimental results. The PJP flow field has a complex vortical system, the evolution of which determines the wake instabilities. The tip clearance leakage vortex first exhibits short-wave instabilities, and the destabilization process then accelerates under the effects of duct shed vortices, which promote the generation of secondary vortices. The secondary vortices further enhance the destabilization process and lead to chaotic evolution. The stator blade root vortices are strongly affected by the rotor blade root vortices, causing an exchange of vorticity that depends on the relative intensity of the two sets of root vortices. The instability of the hub vortices is apparently related to the upstream vortices. The correlation between the tip clearance leakage vortices and the instability of hub vortices is very weak.