Development and assessment of CFD methods to calculate propeller and hull impact on the rudder inflow for a twin-screw ship

The purpose of this study is to investigate the feasibility of a simple but robust approach for the identification of the main interaction effect of hull and propeller on the rudder inflow in a conventional manoeuvring simulator. The manoeuvring simulator adopts a modular/MMG based approach in which the hull, the rudders and the propellers are described by separate mathematical models which take into account the interaction phenomena. The propeller-rudder interaction factor is examined by means of a numerical model developed in OpenFOAM for the prediction of the performance of a rudder in behind propeller condition. Differently the hull-rudder interaction factor is numerically obtained by means of two different approaches. The proposed kinematic method shows the minimum additional computational cost without loss of accuracy. It is based on the analysis of rudder inflow fields (in a PIV fashioned), therefore It can be carried out in a post-processing phase of CFD simulations adopted to extract the hydrodynamic coefficients. This study validates the method by comparing it with the classical approach also used in the experimental campaign, based on the analysis of rudder forces from virtual captive tests. The approaches demonstrate to improve the overall accuracy of the main manoeuvring parameters with respect to the ones obtained by means of a calibrated semi-empirical model.