Turning ability analysis of a fully appended twin screw vessel by CFD. Part I: Single rudder configuration

The turning circle manoeuvre of a naval supply vessel (characterized by a block coefficientCB~0.60) is simulated by the integration of the unsteady Reynolds-Averaged Navier Stokes equations coupled with the equations of rigid body motion with six degrees of freedom. The model is equipped with all the appendages, and it is characterised by an unusual single rudder/twin screws configuration. This arrangement causes poor directional stability qualities, which makes the prediction of the trajectory a challenging problem. As already shown in previous works, the treatment of the in-plane loads exerted by the propellers is of paramount importance; to this aim each propeller is simulated by an actuator disk model, properly modified to account for oblique flow effects. The main goal of the present paper is to assess the capability of the CFD tool to accurately predict the trajectory of the ship and to analyse the complex flow field around a vessel performing a turning manoeuvre. Distribution of forces and moments on the main hull, stern appendages and rudder are analysed in order to gain a deeper insight into the dynamic behaviour of the vessel. Validation is provided by the comparison with experimental data from free running tests.