Enhancing lift and reducing wingtip vortices using a passive rotor on finite-span wings

Abstract

Finite-span wings lose lift compared to infinite-span wings due to the presence of wingtip vortices. Extensive efforts have been made to alleviate the impact of wingtip vortices; e.g., winglet is a widely adopted technique. Although winglets have proven effective in mitigating these impacts, residual vortices still persist in the aircraft wake. In order to address this issue and enhance lift, we propose a passive rotor concept. This rotor utilizes the free-stream flow to spin opposite to the wingtip vortex. As such, the strength of the wingtip vortex is suppressed, leading to an improvement in lift performance. A wing model with the Clark Y-14 airfoil was selected to test the performance of the passive rotor. Lift and drag measurements were conducted at three different Reynolds numbers and a wide range of angles of attack. Three configurations are compared: a plain wing model, a winglet configuration, and the proposed rotor-wing system. The results indicate that the passive rotor outperforms the winglet in enhancing lift, especially at low Reynolds numbers (100,000). Additionally, flow visualization demonstrated the rotor's capability to break the wingtip vortex in the wake. However, at higher Reynolds numbers, the passive rotor exhibited increased drag, resulting in a lower lift-to-drag ratio compared to the winglet configuration. In conclusion, the passive rotor concept shows promising potential to enhance lift and mitigate wingtip vortices in finite-span wings.