Study on the Influence of Direction of Rotation of Propellers in a Push-Pull Contra-Rotating Propulsor

Model Test is a key part of the entire ship design process. The interaction between the propulsor and the hull in these tests is expressed in terms of standard coefficients and forms an important design aspect which affects the final performance of the vessel. Even though these coefficients give important insight for the designers about the overall performance of the propulsor, however, it still lacks detailed information on the sources of these coefficients. The paper studies two design aspects namely the direction of rotation of propellers and the asymmetric strut of a Push-Pull CRP. The study is carried out using a hybrid Reynolds-Averaged Navier-Stokes (RANS) approach where a vortex-lattice code (VLM) is coupled to a RANS solver. The code is validated against model test results before a detailed flow analysis is made. The study shows that the choice and design of the asymmetric strut are very critical in Push-Pull CRP and hold a significant impact on the loading of the pair of propellers. The choice of direction of rotation of propellers is also quite important to ensure a favourable inflow condition to the strut and the load distribution on propellers. The impact of both these aspects on the design of propellers cannot always be determined by propulsive coefficients measured at model tests and needs a detailed CFD analysis.