Force and Flow Characteristics of a Partially Submerged Propeller

Doktorsavhandling, 1996

Model experiments have been conducted to determine the average and dynamic performance of a high-speed partially submerged propeller. The purpose of the experiments was to examine the influence of shaft yaw and inclination angles on the propeller characteristics at different Froude and cavitation numbers and to study the flow around the propeller blades in different conditions. The loads on an individual blade were measured by a stiff five-component balance and a camera equipment recorded flow phenomena of interest. Test results showed on the one hand that a partially submerged propeller, given a proper shaft yaw angle, offers a possible solution for very high efficiency. On the other hand serious vibration and strength problems may arise from resonant blade vibrations. The results have been analysed to ascertain the hydrodynamic origin of various observed force and flow phenomena. Through this analysis, implications for performance prediction theory as well as practice have been pointed out. In addition, basic problems and involved approximations of measurement of dynamic blade load have been addressed. General criteria for the design of an unsteady force measuring system have been outlined, for the case when resonant blade vibration is present. Outlined have been also special similarity law requirements, necessary if the effect of blade vibration observed for a model is to apply to vibrations of larger propellers. Throughout this report, attempts have been made to provide sufficient material so that the experimental results really can be used to validate future theory or repeated experiments.