Numerical simulation of flow around a two-stepped planing hull in calm water

One of the most effective methods for reducing the drag force on planning hulls is the use of steps at the bottom of the ship. A step reduces the wetted surface area and consequently decreases the drag. In this article, the effect of using two transverse steps on the hydrodynamic performance of a hard-chined planning craft is considered with finite element based finite volume method. Navier stokes average time equations are solved with standard k-ɛ turbulence model coupled with volume of fluid equations for simulation of free surface turbulent flow around the hull using the Ansys-CFX software. In order to validate the proposed numerical model in this article, the obtained numerical results are compared against experimental results of Taunton et al. Subsequently, the results pertinent to the drag force, pressure distribution on the hull, the wetted surface, the water spray from the chine and wave pattern around the considered hull are presented and analyzed. Double-stepped planing hulls are found to have smaller drag, since flow separates from the steps and lead to reduction of the wetted surface which itself leads to significant reduction of frictional resistance. Meanwhile, they indicate some negative effects in their hydrodynamic performance in calm water like larger free water elevation behind the transom and larger hydrodynamic pressure in their bow section. It should be mentioned that two-stepped planing hulls have a small variable trim angle in comparison with one-stepped and non-stepped hulls and also improve the control of longitudinal running attitude.