Ishihara D, Horie T
Bioinspir Biomim. 2016 Dec 20;12(1):016008. doi: 10.1088/1748-3190/12/1/016008.
The high torsional flexibility of insect wings allows for elastic recoil after the rotation of the wing during stroke reversal. However, the underlying mechanism of this recoil remains unclear because of the dynamic process of transitioning from the wing rotation during stroke reversal to the maintenance of a high angle of attack during the middle of each half-stroke, when the inertial, elastic, and aerodynamic effects all have a significant impact. Therefore, the interaction between the flapping wing and the surrounding air was directly simulated by simultaneously solving the incompressible Navier-Stokes equations, the equation of motion for an elastic body, and the fluid-structure interface conditions using the three-dimensional finite element method. This direct numerical simulation controlling the aerodynamic effect revealed that the recoil is the residual of the free pitch vibration induced by the flapping acceleration during stroke reversal in the transient response very close to critical damping due to the dynamic pressure resistance of the surrounding air. This understanding will enable the control of the leading-edge vortex and lift generation, the reduction of the work performed by flapping wings, and the interpretation of the underlying necessity for the kinematic characteristics of the flapping motion.
昆虫翅膀高度的扭转灵活性使得在 stroke 反转过程中翅膀旋转后能够产生弹性回弹。然而，由于在 stroke 反转期间从翅膀旋转到在每个半冲程中间维持高攻角的动态过程，这种回弹的潜在机制仍不清楚，此时惯性、弹性和空气动力学效应都有显著影响。因此，通过使用三维有限元方法同时求解不可压缩的纳维-斯托克斯方程、弹性体的运动方程以及流固界面条件，直接模拟了扑翼与周围空气之间的相互作用。这种控制空气动力学效应的直接数值模拟表明，回弹是在非常接近临界阻尼的瞬态响应中，由于周围空气的动压阻力，在 stroke 反转期间扑翼加速度引起的自由俯仰振动的残余。这种理解将有助于控制前缘涡和升力的产生，减少扑翼所做的功，并解释扑翼运动运动学特征的潜在必要性。
