Vessels

摘要

Unsteady turbulent flows in a waterjet propulsion system are investigated at various cruising speeds with the emphasis on pressure fluctuations. The numerical methodology is based on the Reynolds-Averaged Navier-Stokes (RANS) equation with the SST k-ω turbulence model and a sliding mesh technique. The head and efficiency of the waterjet pump are predicted fairly well compared with the available experimental data. The pressure fluctuates intensively in the impeller and the dominant frequency is the impeller rotating frequency with the largest amplitude near the impeller inlet. Besides, two dominant frequency components exist in the intake duct and the diffuser. A high-frequency component is caused by the rotor-stator interaction, and another component is generated by the unsteady vortex evolution in the diffuser passage and would propagate upstream to the impeller and the intake duct. Analyses based on the vorticity transport equation demonstrate the great contribution of the vortex stretching term to the vorticity distribution and evolution in the diffuser. Finally, at the cruising speed of 45 knot, the flows inside the duct are strongly affected by the impeller rotation and present a periodic prewhirl motion with the dominant frequency of the impeller rotating frequency.