| Summary: | When a fluid flows past a lifting surface, tip vortices are created. On marine
propellers, these tip vortices reduce the efficiency of the blades and can have a number of
other undesirable effects if cavitation occurs. Several propeller modifications have been
proposed to suppress tip vortex roll-up, reduce the strength of the vortices, and prevent
tip vortex cavitation from occurring. One of these modifications involves attaching a
flow-through duct to the tip of each propeller blade. Past research on these ducted tips
has shown promising results.
In this study, experiments were conducted to compare the performance of a
conventional propeller with that of a ducted tip propeller. There were two primary
objectives: to determine the effect of the duct on propeller efficiency, and to determine
how cavitation behaviour changes with the addition of the duct. This research differs
from previous work in that the experiments were conducted in a controlled environment,
allowing for more accurate measurements with fewer uncontrollable external factors that
could affect the data.
The results showed a small decrease in efficiency over a large range of test
conditions. However, the general trends were in agreement with the trends seen in sea
trials conducted by Hordnes and Green (1998), in that the presence of the duct was most
advantageous at high advance ratios.
The addition of the duct dramatically changed the cavitation behaviour. The flow
patterns indicated that the tip vortex was substantially diffused with the duct. Evidence
also suggested that the tip vortex cavitation inception index was reduced. These findings
are in agreement with past research. === Applied Science, Faculty of === Mechanical Engineering, Department of === Graduate
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