Self-propulsion Simulation of ONR Tumblehome Using Dynamic Overset Grid Method

With the great progress in supercomputers and the numerical methods, the application of computational fluid dynamics are advancing rapidly in the field of ship hydrodynamics. And the dynamic overset grid method makes it possible for computing complex ship motions, e.g. ship self-propulsion with moving propellers and rudders. In the present work, CFD-based method coupling with dynamic overset grid technique is applied to investigate the hydrodynamic performance of the fully appended ONR Tumblehome ship model during selfpropulsion condition. Open water performance of propeller and towing condition of bare hull are computed before the self-propulsion simulation. The ship model is fitted with twin rotating propellers and twin static rudders, achieving self-propulsion model point at Fr=0.2 and Fr=0.3, respectively. All the computations are carried out by our in-house CFD solver naoe-FOAM-SJTU, which is developed on the open source platform OpenFOAM and mainly composed of a dynamic overset grid module and a full 6DOF motion module with a hierarchy of bodies. The CFD code naoe-FOAM-SJTU solves the Navier-Stokes equations for unsteady turbulent flows with VOF method capturing free surface around the complex geometry models. During the self-propulsion simulation, a feedback controller is used to update the rate of revolutions of the propeller to achieve the target speed. Detailed information of the flow field during the self-propulsion condition is presented and analyzed. In addition, predicted results, i.e. ship motions and force coefficients, are also presented and compared with the available experimental data. Good agreements are achieved which indicates that the present approach is applicable for the self-propulsion simulation.