3D RANS simulations of shallow water effects on rudder hydrodynamic characteristics

An accurate estimation of the rudder forces and moments is essential for manoeuvrability prediction. Previous research has shown that ships have different manoeuvring performance in deep and shallow water. Before considering the rudder’s contribution to shallow water manoeuvring, it is meaningful to analyse the shallow water effects on the rudder itself. In shallow water, the rudder gets close to the channel bottom. Therefore, mirror effects are expected, which may greatly affect the rudder effective aspect ratio and the generated rudder forces. Instead of high-cost model tests and time consuming full ship CFD simulations, this paper applies 3D RANS methods to analyse the shallow water effects on rudder hydrodynamic characteristics. 3D RANS simulations are carried out with a pressure-based coupled algorithm through ANSYS Fluent 16.2. The turbulence is simulated by a realisable k-e turbulence model. Based on a NACA 0020 profile, the method is validated through a comparison of the CFD results with the wind tunnel tests. Then, NACA 0020 spade rudders with geometric aspect ratios of 1.2 and 1.5 are tested with different tip clearance. Rudder lift and drag coefficients are generated to calculate the normal force coefficient for manoeuvring simulations. Finally, shallow water effects on rudder hydrodynamics are summarised.