The scale effects on the open water performance of a pump-jet propulsor

In this work, the scale effects on the open water performance of a pump-jet propulsor (PJP) with pre-swirl stator are considered and implemented based on systematic numerical calculations. With considering the effects of mesh density and time-step size, the unsteady open water performance at the design advance coefficient both in full scale and model scale is first discussed. Then, the scale effects on open water performance are discussed and quantified. For further understandings, the pressure, velocity field and vortical structures are analyzed. Results indicate that different components of PJP demonstrate different scale effects on open water performance. The rotor shows more pronounced scale effects on high advance coefficients, and its thrust coefficient obtains the improvements in full scale at all operating conditions while the scale effects on its torque coefficient are affected by the advance coefficient. For the duct and stator, they exhibit decreases in thrust coefficient in full scale, and the torque coefficient of stator also decreases. Compared with the model scale, the flow on PJP shows significant differences in full scale. The pre-swirl effects of stator are enhanced, resulting in the lower fluctuation degree of rotor thrust at the design operating point. The stator wake, rotor wake, and tip clearance leakage flow show fewer effects on the outflow of duct. The flow separation on the duct outside is significantly weakened. The tip clearance leakage flow is considerably strengthened, but its development is also more significantly restrained by the higher velocity mainstream together with the shrinkage of duct in the rotor downstream.