Comparison of hydrodynamic performance and wake vortices of two typical types of pumpjet propulsor

Pumpjet propulsor (PJP) is widely used in various underwater vehicles recently. Two types of PJP, the stator-rotor PJP (the rotor is behind the stator) and the rotor-stator PJP (the rotor is in front of the stator), are designed to investigate the difference of the hydrodynamic performance between those two PJPs. Numerical simulations based on the Improved Delayed Detached Eddy Simulation (IDDES) model are carried out. Results show that the rotor-stator PJP has a better balanced torque character than that of the stator-rotor PJP. In addition, the characteristic frequency of unsteady forces acting on each rotor blade is the stator blade passage frequency and its harmonics, while that of each stator blade is the rotor blade passage frequency and its harmonics. The wake vortex structure and the evolution mechanism of both PJPs are discussed and compared. Spiral precession and double-helix breakdown of hub vortex are observed for the stator-rotor PJP. The roll-up process of rotor blade trailing edge vortex sheet for both PJPs is discussed. The short-wave instability and the mutual-inductance instability of tip vortices for PJPs are discussed. The instability of tip and hub vortices of the rotor-stator PJP is more likely to occur.