Effects of a splitter plate on a wingsail for aerodynamic lift enhancement

This study investigates the aerodynamic effects of a rigid splitter plate mounted on a two-element wingsail at a chord Reynolds number of $1.4\times {10}^5$. The splitter plate, serving as a flow control device, is specifically designed for a wingsail operating at an angle of attack of $30°$ with a flap deflection of $50°$, aiming to reduce the no-sail zone of autonomous sailboats. Two-dimensional Unsteady Reynolds-Averaged Navier–Stokes (2D URANS) simulations are conducted to evaluate the effects of splitter plate length ($L^{*}$) and attachment position ($P^{*}$) on aerodynamic performance. Results show that the splitter plate can improve the lift-to-drag ratio by up to 39 % when $P^{*}=0.5$ and $L^{*}=0.1$. For shorter splitter plates ($L^{*}\le 0.04$), the recirculation region over the suction side is suppressed, thereby weakening the lifting vortex and reducing the lift coefficient. As $L^{*}$ increases, the vortex upstream of the splitter plate grows in both size and strength and intrudes into the recirculation region. Consequently, the lifting vortex is intensified due to its interactions with the vortex upstream of the splitter plate and the shear layer above the wingsail. Furthermore, the lifting vortex is displaced closer to the upper surface of the wingsail due to the limited space between the shear layer and the suction surface, resulting in an increase in the lift coefficient. This article uncovers the mechanisms through which the splitter plate enhances lift and demonstrates the feasibility of employing it as a passive flow control strategy to improve aerodynamic performance under specific sail missions and operating conditions.