The influence of the wake scale effect on the prediction of hull pressures due to cavitating propellers

In this paper, the scale effect on the wake field of ship models is shown to be an important cause of prediction inaccuracies of hull pressure amplitudes at the first blade rate frequency as induced by the cavitating propeller in model experiments. It is investigated how the scale effect on the wake field, caused by failing to adhere to the full scale flow Reynolds number in model scale experiments, affects the propeller loading, cavitation dynamics and eventually hull pressure fluctuations. A RANS code is used to inversely design a scale model hull that generates a wake field more closely resembling the ship scale target wake field than does the geometrically similar (‘geosim’) hull model. As a demonstrator, a non-geosim scale model of a container vessel has been designed, manufactured and tested. Some full scale data is available for correlation purposes. It is concluded that the wake scale effect may largely explain the model to full scale correlation error on the blade rate hull pressure amplitude, and the use of a non-geosim afterbody design may correct for this error.