Effects of drift angle on model ship flow |
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Authors: | J Longo F Stern |
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Institution: | (1) Iowa Institute of Hydraulic Research The University of Iowa, Iowa City, IA 52242, USA e-mail: longo@iihr.uiowa.edu, US |
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Abstract: | The effects of drift angle on model ship flow are investigated through towing tank tests for the Series 60 CB=0.6 cargo/container model ship. Resistance, side force, drift moment, sinkage, trim, and heel data are procured for a range
of drift angles β and Froude numbers (Fr) and the model free condition. Detailed free-surface and mean velocity and pressure flow maps are procured for high and low
Fr=0.316 and 0.16 and β=5° and 10° (free surface) and β=10° (mean velocity and pressure) for the model fixed condition (i.e. fixed with zero sinkage, trim, and heel). Comparison
of results at high and low Fr and previous data for β=0° enables identification of important free-surface and drift effects. Geometry, conditions, data, and uncertainty analysis
are documented in sufficient detail so as to be useful as a benchmark for computational fluid dynamics (CFD) validation. The
resistance increases linearly with β with same slope for all Fr, whereas the increases in the side force, drift moment, sinkage, trim, and heel with β are quadratic. The wave profile is only affected near the bow, i.e. the bow wave amplitude increases/decreases on the windward/leeward
sides, whereas the wave elevations are affected throughout the entire wave field. However, the wave envelope angle on both
sides is nearly the same as β=0°, i.e. the near-field wave pattern rotates with the hull and remains within a similar wave envelope as β=0°. The wave amplitudes are significantly increased/decreased on the windward/leeward sides. The wake region is also asymmetric
with larger wedge angle on the leeward side. The boundary layer and wake are dominated by the hull vortex system consisting
of fore body keel, bilge, and wave-breaking vortices and after body bilge and counter-rotating vortices. The occurrence of
a wave-breaking vortex for breaking bow waves has not been previously documented in the literature. The trends for the maximum
vorticity, circulation, minimum axial velocity, and trajectories are discussed for each vortex.
Received: 16 September 1999/Accepted: 8 November 2001 |
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