| A three-dimensional low-order potential-based boundary element method for the nonlinear analysis of unsteady sheet cavitation on fully submerged and partially submerged propellers subjected to time-depended inflow is presented. The emphasis is placed on the modeling of supercavitating and surface-piercing propellers. The unsteady cavity surface is determined in the frame work of a moving mixed boundary-value problem. For a given cavitation number, the extent and thickness of the cavity surface is determined in an iterative manner at each time step until both the prescribed pressure and flow tangency conditions are satisfied. The cavity detachment location is also determined in an iterative manner by satisfying the Villat-Brillouin smooth detachment condition. The current method is able to predict complex types of cavitation patterns on both sides of the blade surface, as well as the extent and thickness of the separated region behind non-zero thickness trailing edges. For surface-piercing propellers, the linearized free surface boundary condition is applied along with the assumption of infinite Froude number, both of which are enforced by the negative image method. The method is shown to converge quickly with grid size and time step size. The predicted cavity planforms and propeller loadings also compare well with experimental observations and measurements. Finally, a 2-D study to investigate the effects of jet sprays at the moment of blade entry is presented. |
