Team New Zealand, defenders of the America’s Cup, are using FLUENT to help them gain competitive advantage in the upcoming race. Their work involves simulating, in a fully predictive manner, air and water flows to improve sail configurations, hull shapes, and rudder locations at different boat speeds. For many years, the mainstay of maritime CFD has been panel codes that use inviscid boundary element techniques. These codes make the basic assumption that the viscosity of the affected region is a relatively small volume of the total flow field and that the flow is nonrotational inside the domain – an assumption not made in FLUENT.

The load distribution on the wing shown here indicates that a tapered wing would be more efficient.

FLUENT gives Team New Zealand a more powerful tool with which to perfect their designs, which is proving to be far faster and less expensive than wind tunnel and towing tank studies. So far, several appendage set designs for the yacht have been simulated. The effective span calculated from these results is in close agreement with test tank data and the calculated load on the winglets also agrees well with full-scale measurements.

Analysis of a typical America’s Cup class yacht appendage set

Team New Zealand is modeling the keel wake trajectory, visualized using pathlines emitted from the trailing edge of the fin. This information is useful for optimizing the rudder position. The analysis results also make it possible to position the paddlewheel – the boatspeed sensor – away from local flow accelerations. Boat speed is used in a large number of calculations for wind speed, tide, time to next mark, etc., so positioning it in an optimum location improves the accuracy of this information in the racing environment while deflections of the structure take place.

FLUENT is also being used to study two-dimensional foil sections at or beyond stall conditions. Typically, keel areas are chosen to minimize drag in the upwind sailing condition. During the tight maneuvering of prestart circles and mark roundings, the lift coefficient required to prevent the yacht from drifting sideways can force the appendages to stall. Candidate sections have been modeled in the stalled condition to find those sections with softer stall characteristics and higher lift in the stalled condition.

The recirculation behind the mast tube of a yacht.

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