For high speed crafts it is often necessary that the propeller be operated under inclined flow conditions. This results in generation of cloud cavitation in the root region leading to erosion. Therefore it is thought necessary that the effect of boss be taken into account in such a case. In the present report as a first step in analysing this problem, the effect of boss in uniform flow was studied. In the theory based on Vortex Lattice Method the boss was represented by a series of source rings the strengths of which were determined from tangency condition on the boss surface. Experiments were performed to measure the pressure distribution on the blade near the root region and also on the boss surface. Theoretical results had been found to agree well with the experimental ones.

SummaryIn the first report the authors discussed about the analysis in uniform flow.Using the same discrete model, the analysis for the present report was performed for the oblique case. In addition to the effect of boss, propeller slipstream asymmetry was also incorporated into the model. Experiments were performed by inclining the propeller shaft with respect to the flow direction in the cavitation tunnel.Predicted cavity extents had been found to agree relatively well with the observed ones when the predicted values were advanced by sixty degrees. In the calculation of pressure distribution on the blade, it had been found that there was a considerable drop in pressure at about 60% chord position of the blade near the boss and this position had been found to agree very well with the observed position of root cavitation erosion.