Validation of a full scale CFD simulation of a self-propelled ship with measured hull roughness and effect of welding seams on hull resistance

This study presents the verification and validation of a full scale self-propulsion computational fluid dynamics (CFD) model including measured hull roughness and welding seams. The reference for validation is comprised of speed trial data from five sister ships. To ensure numerical accuracy, resistance and propeller open-water CFD simulations are verified and validated against model tests from two different towing tanks and discrepancies are found to be within the experimental uncertainty of model scale testing. The self-propulsion CFD results emphasise the necessity of measuring hull roughness for accurate performance calculations with discrepancies less than 3.4% on the delivered power relative to the fitted speed trial results. It is found that the empirical Townsin/Mosaad roughness formulation with measured average hull roughness, as recommended by ITTC, provides similar results, as modifying the wall functions using the Colebrook/Grigson roughness function. Homogeneous and heterogeneous roughness modelling methods are found to provide similar results for the studied ship. Modelling of the transverse welding seams on the hull surface is found to increase the total resistance by approximately 0.1% per seam, resulting in a total estimated increase in resistance of 1.5–1.8%. Finally, adding a fairing is found to significantly reduce the resistance penalty from welding seams.