Numerical and experimental analysis of the flow around a two-element wingsail at Reynolds number 0.53 × 106

The rigid wingsail is a propulsion system, utilized in sailing competitions in order to enhance the yacht performance in both upwind and downwind conditions. Nevertheless, this new rig is sensitive to up- stream flow variations, making its steering difficult. This issue suggests the need to perform a study on wingsail aerodynamics. Thus this paper reports some investigations done to better understand the flow physics around a scaled model of an America’s Cup wingsail, based on a two-element AC72 profile. First a wind tunnel test campaign was carried out to generate a database for aerodynamic phenomena analyses and CFD validation. Unsteady RANS simulations were performed to predict and validate the flow charac- teristics on the wingsail, in the wind tunnel test conditions. The wind tunnel domain was fully modeled, in order to take into account the facility confinement effects. Numerical simulations in freestream and wind tunnel conditions were then compared with experimental data. This analysis shows the necessity to consider the wind tunnel walls when experimental and numerical data are compared. Numerical sim- ulations correctly reproduce the flow field for low-to-moderate flow angles. However, discrepancies on the pressure distribution increase when the boundary layer starts to separate from the wingsail. In this regard, the flow generated by the slot between both elements of the wingsail is of paramount impor- tance. This slot flow is analyzed in details through PIV measurements and numerical simulations. While the numerical simulation correctly predicts the jet flow itself, it only partially reproduces the interaction between the jet flow and the main flow, especially at high angle of attacks. More precisely, the numerical simulation fails to predict the correct jet flow trajectory, which affects the lift capabilities of the entire wing. The influence of the wingsail deformation during experimental campaigns has been investigated to explain this behavior