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Unsteady Tip Leakage Vortex Phenomena in a Ducted Propeller
Chunill Hah and Yu-Tai Lee

A detailed numerical study was performed to investigate the flow field near the blade tip in a ducted propeller. The primary objective was to understand the physics of cavitation inception in a ducted propeller. Steady flow analysis does not seem to properly reproduce measured cavitation inception. The flow field near the tip section is unsteady due to interactions between the tip leakage vortex, the trailing edge vortex, and vortex shedding in the wake. To capture relevant flow physics as much as possible, a Large Eddy Simulation was applied in the current investigation. The present study reveals that periodic interaction between the trailing edge vortex and the tip leakage vortex creates stretching and deformation of the tip leakage vortex. This interaction creates a local low-pressure core in the tip leakage vortex. The core pressure in the tip leakage vortex decreases even further when it is stretched and twisted by other nearby vortices. Cavitation inception occurs at about 50% blade chord downstream of the trailing edge.

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