Towards a CFD-based prediction of ship performance - progress in predicting full-scale resistance and scale effects

This paper discusses scale effects on the viscous and wave resistance of ships, as found from CFD computations; and compares these with the usual assumptions in the extrapolation of model test results to full scale. For some different ships computations of the viscous flow and wave pattern have been made for model and full scale, using the free-surface RANS code PARNASSOS. For these cases the viscous resistance appears to be approximately proportional to flat-plate frictional resistance (constant form factor 1+k), but relative to the ITTC 57 line 1+k increases clearly from model to ship. Computed scale effects on the wave pattern are reviewed. For a containership a 20% scale effect on wave resistance is found. A standard extrapolation method applied to the model-scale resistance here underestimates the full-scale resistance by 10%, but the empirical correlation allowance approximately corrects for that difference. This work shows how methods to predict fullscale resistance could be improved using results of today’s CFD methods.