A new type of Gurney flap is applied for energy extraction enhancement of a flapping airfoil. Two-dimensional Navier-Stokes simulations at Re = 10(4) 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 theta(0)). 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 h(g) at first between h(g) = Oc-0.3c (c is the airfoil chord length), while a further increase in h(g) provides no further energy extraction enhancement. Besides, the increasing h(g) results in stronger trailing edge vortices and higher drag force. (C) 2016 Elsevier Ltd. All rights reserved.