All drag and no lift… with the wing locked inside-out, major disaster is looming for Emirates TNZ during race 8 of the 34th America’s Cup; somehow the grinders kept their heads down, pumping away to deliver just enough hydraulic pressure for wingman Glenn Ashby to flip it through…
Less complex than we thought
Ivor Wilkins caught up with the aero team behind Emirates Team New Zealand’s pair of AC72 wing rigs
When the AC72 rule for the 34th Amer- ica’s Cup was first revealed early analysis suggested that the shift to hard wings would be the area where most of the per- formance gains would be sought and found. By the end of the regatta, of course, the attention had shifted to foiling, which proved to be the primary game-changer. However, a paper delivered at the fifth High Performance Yacht Design Confer- ence held in Auckland during the Volvo race stop provided a useful insight into the design and development of the Emirates Team New Zealand wings. It reveals that a planned two-stage wing development programme was in effect stopped at stage one when it was decided that the potential performance gains from refinements in the wing design would be small in comparison with gains being generated by the hydro- foils and the platform aerodynamics. Early design work on the wing had investigated upwind and downwind performance as essentially two different
problems. However, foiling moved the apparent wind so far forward that the boats were virtually constantly in an upwind mode, albeit with very different apparent wind profiles. Consequently, the team’s second wing was basically identical to the first, although there were refine- ments to reduce weight and improve laminar flow in the upper half; this decision had cost benefits, but also had a strategic advantage in that it made the wings or parts of wings interchangeable. The HPYD paper was prepared by Steve Collie, Burns Fallow, Nick Hutchins and Harold Youngren and presented by Fallow. The design process began with an expectation that the introduction of a wing would pose a ‘major aerodynamic design challenge requiring a wide range of new expertise’.
However, ‘As it turned out, the design process involved some new tools and tricks, but was largely a refinement of the computational approach and methods used in the 32nd America’s Cup [in ACC mono- hulls]. The main difference from previous America’s Cups was the increased fidelity and sheer volume of simulations afforded by the computational resources that we now have access to,’ the authors report. Having to operate within tight timeframes from the start of the design process in November 2010, a series of six
design milestones was established for Wing One, with a second development wing scheduled within eight months of the July 2012 launch.
Wing 0 was designed at the first meeting without the use of any simulation or analysis, with a 1:20 scale model being built for testing in the University of Auckland’s Twisted Flow Wind Tunnel under the guidance of David Le Pelley. The tests confirmed predictions that the flow was ‘significantly different from what we were expecting for the full-scale AC72, so no further wind tunnel tests were performed in that campaign’.
However, the tunnel was useful as an educational tool for members of the design and sailing team with no experience of wings. ‘It allowed us to come together for the first time to discuss wing and sail aero- dynamics and trim with a physical tool we could use to visualise and manipulate.’ Having established that the design process would be entirely computational, performance metrics were evaluated using a custom VPP, Gomboc, developed by Dan Bernasconi. The complexity of the perfor- mance factors involved demanded consid- erable computing power (a 576 core Dell HPC cluster was purchased) and extensive automation of the simulation process. ‘As the VPP matured and became more sophisticated… we relied implicitly on the
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GILLES MARTIN-RAGET
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