Application of a Boundary Element Method in the Prediction of Unsteady Blade Sheet and Developed Tip Vortex Cavitation on Marine Propellers

Abstract

Most marine propellers operate in nonaxisymmetric inflows, and thus their blades are often subject to an unsteady flow field. In recent years, due to increasing demands for faster and larger displacement ships, the presence of blade sheet and tip vortex cavitation has become very common. Developed tip vortex cavitation, which often appears together with blade sheet cavitation, is known to be one of the main sources of propeller-induced pressure fluctuations on the ship hull. The prediction of developed tip vortex cavity as well as blade sheet cavity is thus quite important in the assessment of the propeller performance and the corresponding pressure fluctuations on the ship hull. A boundary element method is employed to model the fully unsteady blade sheet (partial or supercavitating) and developed tip vortex cavitation on propeller blades. The extent and size of the cavity is determined by satisfying both the dynamic and the kinematic boundary conditions on the cavity surface. The numerical behavior of the method is investigated for a two-dimensional tip vortex cavity, a three-dimensional hydrofoil, and a marine propeller subjected to nonaxisymmetric inflow. Comparisons of numerical predictions with experimental measurements are presented.