Water Quality Effects on Sheet Cavitation Inception on a Ship Propeller Model

Cavitation research for the maritime industry is mainly carried out in model scale facilities such as a cavitation tunnel or a depressurized towing tank. A first requirement for correctly scaled results is that cavitation inception occurs at the vapour pressure. Each facility has developed its own methods to ensure this, such as controlling the dissolved gas content, application of leading edge roughness or the free-stream nuclei content or a combination of these. A fundamental understanding of the inception mechanism, especially for sheet cavitation on roughened propeller blades, is still missing. Therefore, experiments have been conducted in MARIN‟s Depressurized Towing Tank at various dissolved gas and free-stream nuclei contents with a propeller model which was tested extensively before. A conceptual model for sheet cavitation inception is presented which explains the experimental results. It is concluded that both leading edge roughness and sufficiently small free-stream nuclei are essential for sheet cavitation inception on propeller models.