CFD analysis of lowercase. Phase two (a): Numerical simulation of lowercase, high resolved free surface computations

This report refers to the work that has be done within the Job Order 12-OCT-2015 Phase-2: ''Numerical simulation of lowercase with the propeller and free surface''. Numerical analysis has been performed on the same lowercase geometry provided by FluidTechno Co., Ltd and analyzed in the Phase-1. The geometry has been provided in form of CAD-IGES file. The activity regards the numerical simulations of the flow field around the lowercase, mimicking the experimental campaign carried out in the CNR-INSEAN towing tank "U. Pugliese". For this set of computations the model scale is 2.50, propeller effects are not considered, whereas free surface effects are taken into considerations. This configuration and operative conditions have been already tested and reported previously; three speeds have been tested, namely: 4m/s, 7m/s and 10m/s. Topic of this report is an additional simulation performed with a very fine grid around the surface. This simulation was intended only for an accurate definition of the wave pattern, surface data as well as integral quantities (local and global hydrodynamic loads) are not expected to have any significant change (verification reports a difference in hydrodynamic loads bounded by 2%). Only one speed has been tested, the selected speed is 7m/s. As usual, results are reported in terms of total resistance. Since the focus of this report is the development of the free-surface, example of flow field analysis is mainly given in terms of wave pattern. Verification and validation (i.e. the analysis of the convergence properties and the estimation of both the numerical uncertainty and the comparison error) have been assessed following a widespread adopted procedure. Simulations have been carried out on wall resolved grids (i.e. no wall functions have been used), which count for about 3.5 millions of grid volumes for the description of the lowercase, about 2.1 millions for the background grid (these two parts are the same used in the previous tests) and about 12.6 millions of control volume for the accurate description of the free surface evolution. Therefore, a total of about 18.2 millions of grid points have been used for the discretization of half of the geometry/physical domain (being the configuration symmetrical about the vertical longitudinal plane, no transverse flow or lateral asymmetry has expected to take place). Overlapping grid approach have been used to accurately represent the geometry of the lowercase. Numerical computations have been carried out by means of the Xnavis solver, which is a general purpose unsteady Reynolds averaged Navier-Stokes (uRaNS) solver developed at CNR-INSEAN. For the sake of completeness, the theoretical model adopted at CNR-INSEAN is briefly described in the following, a detailed discussion have been reported in the phase one report.