Numerical investigation into energy extraction of flapping airfoil with Gurney flaps

A new type of Gurney flap is applied for energy extraction enhancement of a flapping airfoil. Two-dimensional Navier-Stokes simulations at Re = 104 are conducted to study the effect of Gurney flaps with various heights. The investigations are undertaken over a wide range of kinematic parameters (reduced frequency k, pitching amplitude θ0). Numerical results show that the application of a Gurney flap notably increases the maximum output power and efficiency compared with a clean NACA0012 airfoil. By affecting the flow structure and the pressure distribution around the trailing edge of the airfoil, the Gurney flap is beneficial to the lift force generation, thus leading to a higher power coefficient. The maximum power coefficient increases with Gurney flap height hg at first between hg = 0c-0.3c (c is the airfoil chord length), while a further increase in hg provides no further energy extraction enhancement. Besides, the increasing hg results in stronger trailing edge vortices and higher drag force.