Lift enhancement for airfoil at high angle of attack using flow-induced vibrations

The lift force of an elastically mounted airfoil experiencing flow-induced vibrations (FIV) in the vertical direction is studied using two-dimensional numerical simulations at the Reynolds number of 800 and high angles of attack. It is found that a lift enhancement as high as 35% can be achieved when the reduced velocity is close to 2. Meanwhile, the maximum lift-to-drag ratio is also enhanced. When the maximum lift is achieved, the vortex wake is featured by an upward-moving vortex-pair, which is formed by a stronger leading-edge vortex (LEV) and a weaker trailing-edge vortex. The physics mechanism of the lift enhancement is analyzed using a modified force element theory. Detailed analysis reveals that a strong LEV generated by the FIV is crucial for the high lift. This work may provide insight into the flow control of nano aerial vehicles.