Downwind sail aerodynamics: A CFD investigation with high grid resolution

A computational fluid dynamics (CFD) code was applied to an America's Cup Class Yacht to investigate sailing performance in a downwind configuration. Apparent wind angles at 45 degrees, 105 degrees and 120 degrees are reported, sailed with mainsail and asymmetrical spinnakers. Numerical results are in good agreement with wind tunnel data. A large mesh investigation was performed, ranging from 60,000 elements up to 37 million elements, which shows a converging trend to the experimental values with differences smaller than 3% in both lift and drag. The most commonly used turbulence models in sail applications were tested and the results are presented here in two meshes with I million elements and 6.5 millions, respectively. All turbulence models over-estimate forces more than solving the Navier-Stokes system without any additional equations, hence turbulence models do not increase solution accuracy according to these results. (C) 2009 Elsevier Ltd. All rights reserved.