Towards accurate wake predictions of twin-screw ships with an open-shaft stern configuration
Author Windt, J.
Title Towards accurate wake predictions of twin-screw ships with an open-shaft stern configuration
Conference/Journal NUTTS 2003 symposium, Rome
Month September
Year 2003

Many twin-screw ships have a so-called open-shaft stern configuration. While in most cases the hull has a geometrically simple shape, the protruding shafts, bossing and supporting struts make the over-all geometry complex. This geometrical complexity and possibly the shaft rotation cause the behaviour of the flow near the shafts and brackets to be complicated as well, and it is a challenge to be able to make reliable numerical flow predictions.
As a first step in establishing this capability at MARIN, using the PARNASSOS code (see [1]), we have considered the calculation of the viscous flow around an inclined non-rotating cylinder protruding from a flat plate. In 1997, Pinard [2] investigated this kind of flow experimentally. In 2001, Hally [3] predicted the flow using a viscous flow solver and compared the calculations with the experiments; the agreement between numerical and experimental data was found to be good. As a second step we studied the same case but now with the cylinder rotating about its axis. Finding serious difficulties, we reduced the complexity of the case by considering the flow along a rotating (around its axis) cylinder aligned with the main flow. The flow along the rotating cylinder was investigated experimentally by Lohmann [4] in 1976 and investigated numerically in 1982 [5].
The inclined cylinder test case is used to investigate the possibility to incorporate the shaft in real ship calculations when applying the same kind of grid topology, i.e. an O-H type, that is usually being applied at MARIN. The flow around the flow aligned rotating cylinder is used to test the implementation of the new boundary condition in the PARNASSOS code, to investigate the necessary grid density in case of rotation and to reveal imperfections of turbulence modelling.

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