Boundary element method for the analysis of the unsteady flow aroundextreme propeller geometries

The unsteady flow around a marine propeller subject to a spatially nonuniform inflow is analysed by utilizing a time-marching potential-based low-order boundary element method. Constant strength dipole or source distributions are used on each of the quadrilateral panels representing the propeller blades and their trailing wakes. Linear dipole distributions are used at the first wake panels adjacent to the blade trailing edge in order to render the method insensitive to the time step size. An efficient algorithm is implemented in order to ensure an explicit Kutta condition (i.e., pressure equality) at the blade trailing edge at each time step. The numerical method is shown to be consistent with known analytic solutions for two-dimensional unsteady flows. The robustness of the method is tested in the case of a highly skewed propeller in a given wake inflow and the results are shown to converge quickly with number of panels for a broad range of reduced frequencies.