Sheet Cavitation on Propeller Blades
Cavitation has a huge impact on the character of the pressure fluctuations induced by the propeller motion. The amplitude of the pressure fluctuations in non-cavitating condition is much smaller than in the cavitating status. The greater amplitudes in case of cavitation can be explained by the thickened profile of the propeller blades generated by the cavitation layer. Cavitation can also lead to a thrust decrease and increase the amplitude of pressure fluctuations by approximately 10 times. For this reason, the dependency of the pressure fluctuations on cavity volume and cavity extension on the propeller blade have to be investigated. Particularly, the change of cavity thickness in time is of a great interest for the computation of pressure fluctuations.
At the current time a steady partially non-linear cavitation model is implemented in panMARE in order to calculate the sheet cavity extension on propeller blades. The algorithm is based on the assumption that the cavity thickness is small compared to the blade profile such that the boundary conditions for the cavity calculation are considered on the blade surface and not on the exact cavity surface. The model is able to simulate sheet cavitation on bodies like hydrofoils and propellers and was successfully applied to various cases. The pictured cases show the cavitation extent on the KCS-propeller geometry in self-propulsion condition behind the ship model, once in calm water condition and once in two instants of time during the passage of a regular wave. It can be seen that the model allows the prediction of sheet cavitation even in very unsteady inflow conditions.
Figures taken from:
- Heinke, H. and Jaksic, D., Untersuchung des Einflusses des Nachstromfeldes (Modell- oder Großausführungsnachstrom) auf die Kavitation und Druckschwankungen am KRISO Containerschiff KS621. Technical report, Schiffbau-Versuchsanstalt Potsdam GmbH, 2003