Numerical and Experimental Comparison of Spinnaker Aerodynamics Close to Curling

When sailing downwind with a spinnaker, the “verge of curling” is one of the common recommendations that sailors follow for efficient sailing. Wind tunnel experiments on spinnaker models conducted by Aubin et al. (2017) in the Twisted Flow Wind Tunnel of the Yacht Research Unit of the University of Auckland have shown that curling can be related to better performance at Apparent Wind Angle ≥ 100°. In the present article, we will focus on the aerodynamic performance jump observed at Apparent Wind Angle AWA = 100°, where the drive force increases up to 15% when the sail starts to flap. Thanks to four triggered HD cameras and coded targets stuck on the sail, three flying shapes of the spinnaker are reconstructed by photogrammetry for different sheet lengths from over trimmed to flapping occurrence. The pimpleFOAM solver from OpenFOAM is used to simulate the aerodynamics of the three rigid extracted flying shapes. Results highlight the ability of the model to simulate the experimental jump observed closed to curling and the significant confinement effect of the roof of the wind tunnel.