Abstract
To reduce fuel oil costs and emission of greenhouse gases of ships in operation, application of Contra-Rotating Propellers (CRP) will be one of the solutions, which have high propulsive efficiency. Although several estimation methods of predicting open water characteristics of CRP have been developed in the past, few methods treat accurately with trailing wake geometry, which influences much on estimate accuracy. CRP makes the flow around the propellers more complicated compared with conventional single propeller because aft and forward propeller of CRP interacts each other strongly. In order to improve estimate accuracy, more rigorous treatment of the trailing wake geometry is desirable. This paper presents a calculation method, taking deformation of trailing wake accurately into account. The method is based on a simplified surface panel method "SQCM" which satisfies the Kutta condition easily. The SQCM consists of Hess and Smith type source panels on the propeller surface and discrete vortices on the camber surface according to Lan's QCM (Quasi-Continuous vortex lattice Method). The wake vortex lines are arranged in accordance with the direction of the flow including induced velocity by both propellers. We show some calculated results and validate them by comparing experiments in this paper. It is found that thrust and torque of the aft propeller differ considerably depending on which the deformation of trailing wake is taken into account or not. The calculated results with deformed wake agrees very well with the experiment, while the calculated results without deformed wake always overestimate the thrust and torque of the aft propeller.
