Resistance prediction using CFD at model- and full-scale and comparison with measurements

This study addresses the numerical prediction of the resistance of the Lucy Ashton, a paddle steamer which was used in an experimental campaign in the 1950s, and for which there is available measurement data at both model-scale and full-scale. This case corresponds to unique conditions where jet engines were used in the propulsion of the hull at ship-scale, circumventing the need for a propeller or the ship to be towed by another vessel and thus avoiding interference effects. The computations were carried out for a range of Froude numbers at full-scale, and varying scaling ratios for a constant Froude number. The comparison of the numerical results with the available measurement data shows the simulations to underpredict the resistance for all conditions. The discrepancy observed at full-scale is attributed partially to roughness effects not being included in the computational setup, and due to the even keel configuration of the ship in which the simulations were performed. The ITTC 1978 procedure was applied to the model-scale results, and it was found that the scaled resistance coefficient overpredicts the resistance reported in the experimental campaign and the resistance obtained in the simulations when roughness and air resistance are included in the procedure. • Numerical ventilation can be a severe problem at both model-scale and full-scale. • Roughness and ship motions are needed for CFD to agree with full-scale measurements. • Roughness and air resistance play a crucial role in the ITTC 78 scaling procedure.