Drag Reduction due to Stern Interceptors on Naval Vessel Displacement Hull Forms

This study is aimed at studying the hydrodynamics of stern mounted interceptor using CFD. For the purpose of this research, we will use the Oliver Hazard Perry class frigate (FFG-7). For the simulation purpose, we will use OpenFOAM, which has an inbuilt numerical tool known as InterDyMFoam which is a multiphase Navier Stokes equation solver which also allows for dynamics mesh movement. There have been done multiple studies experimentally proving the benefit of such energy saving devices such as Flaps, Wedges and Interceptors. An interceptor is a vertical plate fitted at the transom of the ship. It generates a region of very high pressure by slowing down the flow drastically. Due to this there are 2 consequences: 1) Lift increases 2) Trim reduces. A combination of these 2 effects reduces the drag at a wide range of speeds. This research will aim to find that range of speeds where the interceptors are beneficial using CFD. There has been a previous study [1] which was done using a y+ ≈ 100 and using wall functions. The focus of this study is to use a y+ ≈ 1 and not to use any wall function. This will help in better understanding the boundary layer region of the flow due an Interceptor which is very important for studying the drag reduction benefits. Simulation results will be presented for the hull without the interceptor at multiple speed in the range corresponding to Fr=[0.25:0.44] and for the hull equipped with the interceptor mounted at stern with different strokes (protrusion height off the bottom). These results will be validated against the experimental tests already conducted in the Virginia Tech towing tank. The study also aims to see the effect of different meshing algorithms used for the process of making the mesh as the boundary layer mesh would prove to be the most important part of this exercise. For this, the authors have considered using snappyHexMesh, which is the meshing algorithm of choice in OpenFOAM and cfMesh, which is another opensource meshing algorithm which tends to works very well with OpenFOAM.