Numerical Modeling of Podded Propulsors and Rudder Cavitation

Abstract

Various computational methods that have been developed in the past are combined in this paper to predict: (a) the performance of podded propulsors, and (b) the sheet cavitation on a rudder which is subject to the flow of an upstream propeller. An 3-D Euler-based finite volume method (GBFLOW-3D) is used to predict the flow around a pod with a strut, and is coupled with MPUF-3A, a lifting surface vortex-lattice method, which is applied to the propeller(s) of the pod. The propellers are modeled via body forces in GB FLOW. The 3-D effective wake for each of the propellers of the pod is evaluated by subtracting from the total inflow (determined in GBFLOW-3D) the velocities induced by the same propeller ( determined in MPUF-3A). Several iterations between GBFLOW-3D and MPUF-3A are performed until convergence is reached. The three-way interaction among the pod/strut and the two propellers is fully accounted for at the end of the iterative process. The inflow to the rudder is determined by applying GBFLOW-3DIMPUF-3A on the propeller upstream. Once the propeller-induced flow to the rudder is evaluated, PROPCAV (a potential-based boundary element method), is used to predict the cavitation patterns on the rudder. The effects of the hull are considered by using the image model in PROPCAV. Several validation studies with other methods, some analytical solutions, and experiments are presented.