拍动迎角对扑翼悬停飞行气动特性影响的数值模拟研究

Numerical Simulation on the Effect of Angle of Attack on Aerodynamic Forces about Flapping Wing in Hovering Motion

摘要: 为了研究悬停状态下扑翼飞行的运动参数对其所产生的非定常气动力影响，本文通过数值模拟方法模拟了不同拍动迎角条件下以提前翻转模式往复拍动二维平板的流场演化特性。通过比较不同迎角算例的瞬时与平均气动力，得到了不同迎角下的气动力变化规律。在拍动迎角增加的过程中，总共有四个因素受到迎角的影响，即尾迹捕捉机制，翻转机制，失速延迟机制，拍动迎角对气动力的升力分量的影响。在拍动行程开始的加速阶段，气动力主要受平板–涡相互作用的影响。而在匀速平动阶段，大迎角条件下的拍动由于受附着前缘涡的作用，可产生较大的升力，但若继续增大迎角会导致气动力的升力分量减小。在最后的减速–翻转阶段，由翻转机制提供的气动力随着迎角的增加而减小，这主要是因为大迎角拍动的平板对应着更小的转动的角速度，导致附加环减小，从而降低升力分量。综合上述各种机制的影响，对于所研究的拍动模式，扑翼的时均升力系数在拍动迎角为55度附近存在一个极大值，进一步增加迎角会导致升力的减小。

Abstract: In order to study the effect of kinematic parameters on aerodynamic force of flapping wing in hovering motion, the evolution of flow fields about a plate with advanced rotation under different angle of attack is numerical investigated. The result shows the variation of instantaneous lift coefficient and time averaged lift in different angle of attack. There are four mechanism changes by angle of attack, wake capture, rapid pitch rotation, stall delay, and the influence of angle of attack on the component of aerodynamic force on lift. In the beginning of the stroke, the aerodynamic force is mainly affected by plate-vortex interaction. In the constant velocity phase, the plate at high angle of attack can generate high lift by the leading edge vortex. However, a higher angle of attack can also reduce the component of aerodynamic force on lift. At the rotation-declaration phase, as the rotational velocity in the case with high angle of attack is lower than that of the case with small angle of attack, the added circulation and lift are also reduced. Considering the influence of the above mechanisms in the flapping motion present studied, there is a maximum value of the time-averaged lift coefficient of flapping wing near the angle of attack of 55 degrees, and further increase of the angle of attack will lead to the decrease of lift.