Inclined shaft propeller flows

Courts, Malcolm David (1980) Inclined shaft propeller flows. University of Southampton, Doctoral Thesis.

Abstract

Most planing boats and other high speed craft driven by water screw propulsion have their propellers on an inclined shaft leading to an oblique inflow relative to the propeller axis. There is thus a circumferential variation of the tangential component of the inflow to the blade giving rise to a cyclic variation in blade load. This work details the results of an experiment investigation into the flow field around such a propeller and various methods of predicting, theoretically, overall propeller performance on an inclined shaft in non-cavitating flows. The experiment work utilised the recently developed technique of laser doppler anemometry. An instrument operating in the 'reference beam' mode and capable of the simultaneous measurement of two velocity components was used to obtain real time velocity records at various points in the flow field around a propeller in a cavitation tunnel. The technique does not rely on any probes within the flow and so enables information to be obtained very close to the propeller. Response time is rapid enough for all flow unsteadiness to be recorded. Several theoretical models were developed to predict propeller performance using unsteady 2D foil theory. The limited scope of these theories led to the development of an unsteady lifting line model based on published lifting surface methods. Incorporated into this model are arbitrary wake orientation, an image system and the facility to predict field point velocities and hull pressures. Correlation with experiment results shows reasonable agreement for mean velocity levels within the known limitations of the model used.

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