Taper ratio influence on the performance of 3-D cavitating hydrofoils moving under free surface

Abstract

Taper ratio influence on the performance of three-dimensional (3-D) cavitating hydrofoils moving steadily under a free water surface has been investigated numerically. An iterative boundary element method (IBEM) developed before has been modified and extended to solve this problem. The fluid is assumed to be inviscid, incompressible and the flow irrotational. All variables and equations are made non-dimensional to achieve a consistent numerical scheme and a very quick convergence. The IBEM solves the hydrofoil problem and free surface problem separately with the effects of each other via their potential values in an iterative way. Both the 3-D hydrofoil surface and the free surface are modeled with constant strength source and constant strength doublet panels. The results of the method was first validated with those of a tapered wing. Later, it is applied to a tapered hydrofoil and the effects of taper ratio on cavitating hydrofoil performance have been investigated. It has been found that taper ratio causes a decrease in drag coefficient on cavitating hydrofoil thereby it causes an increase in lift-drag ratio in unbounded flow domain. Taper ratio also causes an improvement slightly the lift-drag ratio of the cavitating hydrofoil moving under a free surface.