For a competitive design of energy efficient rudder propeller configurations, it is essential to produce quick and reliable results during the early design stage. Since many configurations should be tested, the time for modelling and for the calculation itself need to be kept as low as possible while still obtaining reliable results.The final comparison of different designs is still carried out during model tests. In these tests, the Reynolds number is different compared to the actual ship, which is why viscous effects are not represented correctly. In the evaluation of the rudder performance, the drag and a prediction of the stall behavior are viscous effects of main interest. The drag is mainly of interest for the evaluation of the performance of the rudder, whereas the prediction of stall is important as well. Due to low Reynolds numbers in model scale, stall can even occur at straight ahead condition at the rudder which would then lead to incorrect performance predictions if this stall behavior does not occur in full scale. In full scale, the stall behavior at large rudder angles is of interest for the evaluation of the maneuvering forces of the rudder.The method presented in this paper is based on an earlier work of the author, in which a steady boundary element method (BEM) was coupled with a steady lifting line approach (LL). Using this approach, the propeller rudder interaction can be taken into account and the computational effort for wake alignment within the BEM can be reduced significantly while maintaining high numerical stability.As this coupled BEM-LL method is based solely on potential theory, the aforementioned viscous effects cannot be considered properly. To overcome this drawback, this paper deals with a two-way coupling of the existing three-dimensional BEM-LL with a two-dimensional boundary layer method (BL). The BEM-LL deals with the potential outer flow, whereas the viscous flow at the rudder surface is calculated within the BL. Different approaches are applied and compared for the mapping between the three-dimensional BEM-LL and the two-dimensional BL method. The coupled approach is used to improve the calculation of the drag in model and full scale and to give an estimation of the stall behavior of the rudder.The results obtained by the presented method are compared to different model tests conducted for a container ship. In addition to the standard model tests (resistance, open water and propulsion test), reverse open water tests with propeller and rudder were carried out to investigate the model scale propeller rudder interaction in detail.

Coupling of a Boundary Element Method With a Boundary Layer Method for Accurate Rudder Force Calculation Within the Early Design Stage

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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