Investigation of wind tunnel experiments on nonlinear ground effect for flying cars

This research investigates the nonlinear aerodynamic characteristics of ground effect for flying cars, utilizing high-precision balance measurements to determine the lift and drag of flying cars and particle image velocimetry (PIV) in a closed-circuit low-speed recirculating wind tunnel. The ground effect's lift enhancement mechanism was revealed through analysis of aerodynamic results and flow field structures. Force measurement experiments demonstrated that ground effect significantly improves aerodynamic performance, with the lift coefficient showing a nonlinear trend as altitude decreases, undergoing the gentle force phase, the force increase phase, and the force reduction phase. PIV results indicated that the narrowing flow channel between the flying car and the ground at lower heights reduces airflow speed beneath the wing, converting kinetic energy into pressure potential energy, similar to a high-pressure air cushion. Consequently, airflow speed over the upper wing surface increases, enhancing lift. Additionally, ground effect causes the wingtip vortex structure to move upward and outward along the wing span, reducing downward induced velocity, weakening vortex strength, and increasing the effective aspect ratio of the three-dimensional wing. These changes reduce induced drag, thereby improving the overall performance of the flying car.