Scientific wing Analysis By Alessandro Fiumara – Assystem France and ISAE-Supaéro; Julien Senter – Assystem France; Nicolas Gourdain & Vincent Chapin – ISAE-Supaéro; and Prashanth Shankara – Siemens PLM Software
The America’s Cup, affectionately known as the “Auld Mug,” is the oldest sporting trophy in the world dating back to 1851. Pushing the limits of sailing and sailors alike, the prestigious competition has seen a surge of interest in recent years riding on the coattails of fast yachts, technological innovations, high profile athletes and teams backed by billionaires.
Catamarans introduced in the 2013 America’s Cup were faster than the wind, thanks to the introduction of hydrofoils and of solid two elements wingsails, which share similarities with high-lift aircraft wings. The wingsails were based on rules and guidelines outlined in the AC72 class, used in the main race, and the AC45 class, used for preliminary races and training.
The newer class catamarans are unlike any other previous catamarans, reaching twice the wind speed and hydrofoiling on water, leading to a surge in spectator interest. The 35th America’s Cup will be held in June 2017 on the Great Sound of Bermuda and will be raced in the new AC50 class, a wing sail powered, fast, foiling catamaran smaller than the AC 72, manned by a six member crew.
Compared to conventional “soft” sails, a wingsail is much more complex, providing lift with variable camber, controlled by a flexible or jointed structure. The wingsails offer greater aerodynamic efficiency compared to the canonical sails and better performance, as seen by top speeds of around 47 knots (87 km/h) in the races. While this has made the races faster and more exciting to the viewing public, the challenges lie – as always – in handling these wingsails and managing their aeroelastic behavior to achieve the highest performance during navigation.
These wing sails are difficult to control and the research on their stability in multiple scenarios is still evolving. Finding a stable setting in all navigation conditions for these wing sails is challenging and there have already been a couple of instances of catamarans “flipping” or “falling over” due to this instability. As in the aerodynamic stall of an airplane wing, these wing sails can stall during operation and it is crucial for designers to understand their stall behavior under different wind conditions.
To further the understanding of wing sail behavior, a PhD research project was initiated by Assystem France, an international engineering and innovation consultancy, and the Department of Aerodynamics, Energetics and Propulsion (DAEP) at ISAE-Supaéro, the renowned French Aerospace Engineering School.
Read on, courtesy of our friends at The Maritime Executive.