Based on Volume of Fluid (VOF) method of numerical simulation, this paper respectively analyses the propulsive performance of ordinary propeller and ducted propeller when operating close to the free surface. Several working conditions are set including different depth and advance coefficient to explore the influence towards propulsive performance of propeller from the free surface and the duct structure, by comparing the thrust coefficient and the nephogram of the flow field obtained from the simulation. The result shows that when operating near free surface, the propulsive performance gets poorer due to ventilation phenomenon. Under conditions of greater depth (h=0.21m, 0.24m) and a lower advance coefficient (J=0.2, 0.4), the duct structure enhances the stability of propeller thrust. However, when the depth is insufficient (h=0.15m, 0.18m) or the advance coefficient exceeds a certain threshold (J=0.6), the duct adversely affects the propulsive performance due to ventilation effects and flow separation.
Tang et al. (Sun,) studied this question.