Abstract
The influence of free surface for the ducted propeller was investigated based on the numerical simulation in this paper. The ducted propeller consists of a duct with 19A section and the KA4-70 propeller. The immersion ratio was defined as the non-dimensional value between the distance from propeller axis to free surface and diameter of propeller. In this study, 4 immersion ratios were considered as 0.75, 1, 1.25, and 1.5, and the results from each condition were compared to those of fully immersed condition, respectively. As the immersion ratio is decreased, the total thrust and torque of the ducted propeller tend to be decreased, in particular, the portion of thrust reduction on the duct was greater than that of the propeller. It was observed that the pressure on duct is asymmetrically distributed due to the effect of free surface, on the contrary, it is axis-symmetrical in fully immersed condition. And the free surface behind the ducted propeller system is observed in the shape of “V”. As the immersion ratio decreases, the difference between crest and though of free surface was increased.
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