CFD analysis of turning abilities of a submarine model

A detailed analysis of the maneuvering qualities of a submarine vehicle is carried out by means of a general purpose unsteady RaNSe based CFD solver. In particular, free running maneuvering simulations are performed both at infinite depth and close to the free surface (snorkeling operation) at a reference speed corresponding to Fr=0.21; the analysis is restricted to three degrees of freedom (3DoF) maneuvers in the horizontal plane. The submarine model is equipped with two different control device arrangements, namely a cruciform and a X rudder configuration. The numerical results are presented in a phenomenological style and are partially validated with the experiments for the cruciform rudder configuration. Main finding highlights the superior turning abilities of the X rudder configuration with respect to the cruciform one. Moreover, it has been observed that, for the condition investigated and for both configurations, the stern appendages provide a destabilizing force only in the transient phase, while it acts as a fixed appendage during the steady turning phase. The study focuses also on the effect of grid refinement on both the maneuvering loads and the resulting dynamic response of the model. The analysis revealed that, at least for the present geometry and test, a rather coarse grid (order of millions of grid points) provides a reliable prediction of both the trajectory and kinematic parameters, but a rather inaccurate hydrodynamic loads estimation.