Bionic micro aerial vehicles have become popular because of their high thrust efficiency and deceptive appearances. Leading edge or trailing edge devices (such as slots or flaps) are often used to improve the flight performance. Birds in nature also have leading-edge devices, known as the alula that can improve their flight performance at large angles of attack. In the present study, the aerodynamic performance of a flapping airfoil with alula is numerically simulated to illustrate the effects of different alula geometric parameters. Different alula relative angles of attack β (the angle between the chord line of the alula and that of the main airfoil) and vertical distances h between the alula and the main airfoil are simulated at pre-stall and post-stall conditions. Results show that at pre-stall condition, the lift increases with the relative angle of attack and the vertical distance, but the aerodynamic performance is degraded in the presence of alula compared with no alula, whereas at post-stall condition, the alula greatly enhances the lift. However, there seems to be an optimal relative angle of attack for the maximum lift enhancement at a fixed vertical distance considering the unsteady effect, which may indicate birds can adjust the alula twisting at different spanwise positions to achieve the best flight performance. Different alula geometric parameters may affect the aerodynamic force by modifying the pressure distribution along the airfoil. The results are instructive for design of flapping-wing bionic unmanned air vehicles.

仿生微型飞行器因其高推力效率和欺骗性外观而变得流行。前缘或后缘设备（例如插槽或襟翼）通常用于改善飞行性能。大自然中的鸟类也拥有尖端设备，称为alula，可以在大迎角下改善其飞行性能。在本研究中，数值模拟了带有翼片的拍打翼型的气动性能，以说明不同翼片几何参数的影响。不同的Alula相对攻角β（Alula弦线与主翼翼弦之间的夹角）和垂直距离h在失速前和失速后的条件下，模拟了桨叶与主翼之间的距离。结果表明，在失速状态下，升力随相对攻角和垂直距离的增加而增加，但是在没有阿拉鲁的情况下，空气动力性能下降，而在失速后，阿拉鲁的空气动力学性能大大增强。电梯。但是，考虑到不稳定的影响，对于在固定垂直距离处最大升力的提升，似乎存在一个最佳的相对迎角，这可能表明鸟类可以在不同的翼展方向位置上调整alula扭曲以获得最佳的飞行性能。通过修改沿翼型的压力分布，不同的alula几何参数可能会影响空气动力。