Comparative assessment of model-scale extrapolation and full-scale CFD for ship power prediction at design and ballast drafts

Accurate prediction of ship power at the design draft often relies on converting performance data obtained under ballast conditions, as sea-trial measurements are typically available only at the ballast draft. This study proposes a CFD-based framework for predicting full-scale ship power at different drafts by comparing extrapolation from model-scale CFD results and direct full-scale CFD simulations. This framework is applied to the KVLCC2 and MV Regal at design and ballast drafts over a range of ship speeds. Verification and validation are conducted, including assessments of uncertainties related to grid resolution, timestep size, wall Y + treatment, roughness modeling, and body-force propeller (BFP) modeling in full-scale CFD. The extrapolated model-scale results are compared with full-scale CFD predictions. Validation again available sea-trail data demonstrates that, under best-practice numerical settings, the BFP model predicts the delivered power of the MV Regal with a minimum deviation of 4.14%. The uncertainty analysis further indicates that the wall Y + treatment and roughness modeling are the two dominant sources of uncertainty in full-scale simulations. Overall, both approaches provide comparable predictions of resistance, propulsive performance, and delivered power at both drafts, while drafts effects are mainly attributed to changes in the wetted surface area and bow geometry.