Numerical simulation of the flow field and radiation noise from a pump-jet propulsor under various stator pre-whirl angles

The effects of different stator pre-whirl angles on the hydrodynamic and noise performance of a pump-jet propulsor (PJP) are studied; these angles are the inlet, outlet, and stagger angles. The stress-blended eddy simulation (SBES) approach, used to describe flow details around a PJP, is combined with the variational Lighthill's analogy to perform the acoustic calculation. The discrete peaks of the unsteady thrust of a single rotor blade and of all of the rotor blades are located at the harmonics of the blade passage frequency for stator (BPFs) and the blade passage frequency for rotor (BPFr), respectively. The trend in the amplitude with the pre-whirl angle at various harmonics follows no systematic rule, but the excessive pre-whirl angle increases the amplitude in the whole spectrum. With increases in pre-whirl angle, the stator sheet vortex and root vortex are weakened and enhanced, respectively, leading to a reduction of the high turbulent kinetic energy (Tk) regime at the root. Further study of the PJP sound indicates that the discrete tonal noise is located at the BPFs, BPFr, and their harmonics; the pre-whirl angle does not affect these locations, except in the largest inlet angle case. The cases with the least pre-whirl angle have an extremely low noise level, particularly at the outlet angle, which has an obvious downstream directivity.