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Trim wedge optimization using RANS/FS

AuthorsStarke, A.R., Ploeg, A. van der, Veldhuis, C.H.J.
Conference/JournalRINA Developments in Marine CFD
DateMar 22, 2011
It is well-known that even for large displacement ships the application of a trim wedge can reduce the ship resistance by several per cent. At present the dimensions of a trim wedge are typically chosen in the order of magnitude of 1-1.5 per cent of ship’s length, while the height (or angle) of the trim wedge is optimized by model testing. This is relatively time consuming, and thus expensive, since it requires one run through a towing tank for each wedge.
Viscous free-surface flow computations (RANS/FS) also offer the possibility to design or optimize a trim wedge. This requires a high accuracy of these computations, since the differences between resistance values are to be computed. In previous papers we have shown that using our viscous-flow solver PARNASSOS we are capable of doing so.
In the present paper we will compare 3D RANS/FS computations including free trim and sinkage for a ship at a given draught and speed with available experimental data, showing the capabilities of our method. The comparison includes predicted resistance values, stern wave patterns and dynamical trim and sinkage values for various trim wedges.
As the flow off the transom is dominated by viscous effects, it can be expected that the Reynolds scale effect can have a big influence on the flow off a transom, and possibly on the optimum trim wedge. This issue will be addressed as well.


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