An Investigation on the Discrepancies between RANS and BEM Approaches for the Prediction of Marine Propeller Unsteady Performances in Strongly Non-Homogeneous Wakes

In the present work an analysis of the reliability of different numerical approaches, namely BEM and RANSE solver, for the prediction of unsteady performances of marine propellers is presented. To this aim, the well-known Seiun-Maru Highly Skewed Propeller operating in different wakes is considered. The results of this analysis show that, in correspondence to particularly challenging conditions, i.e. when very pronounced ship wakes are present, the two approaches may provide considerably different results in terms of propeller mechanical characteristics and pressure distributions on the blades. This problem, which is implicitly eliminated when the thrust identity approach is applied (as almost always performed, as an example, for propeller analyses aimed to the evaluation of cavitation extension and / or induced pressures), may become critical in case the codes are used for numerical self-propulsion tests, where a high accuracy in the prediction of the unsteady propeller performances in correspondence to a prescribed value of the advance coefficient, instead of the thrust coefficient, is mandatory. The analyses carried out allow to underline which are the potentially more problematic cases, in terms of wakes characteristics, and to suggest some possible reasons of the encountered discrepancies, which will need further analyses to enhance the prediction capability of numerical codes.