Effect of the duct and the pre-swirl stator on the wake dynamics of a pre-swirl pumpjet propulsor

A numerical study based on improved delayed detached eddy simulation is conducted to investigate the flow of a pre-swirl pumpjet propulsor (PJP). The PJP consists of a stator, a rotor, and a duct. In order to separate the roles played by the rotor, stator, and duct in determining the flow of PJP, three models are established: the R model (rotor only), the R–D model (rotor within a duct), and the PJP model (rotor and stator within a duct). Results show that the effect of the duct on the unsteady force acting on the rotor blades is weak, while the pre-swirl stator on it is strong due to the rotor–stator interference. In addition, the vortex structure of the three models are compared. The tip-duct mutual-inductance instability mode that the duct-induced vortex begins to affect adjacent tip vortices is reported. For the PJP model, a unique short-wave instability mode of the tip vortex caused by the existences of pre-swirl stator is discussed. More importantly, for the R–D and PJP model, the transition from stability to instability of the tip vortex depends on both the spiral-to-spiral distance and the strength of duct-induced vortex.