刚性和柔性飞片旋转运动的双稳性
Bistability in the rotational motion of rigid and flexible flyers
摘要：
我们探讨了悬停飞行的旋转稳定性。我们的模型的动机是一个实验性的圆形物体和一个计算性的圆形模拟被动悬停在振荡气流中，这两个系统已被证明在自由飞行过程中保持旋转平衡。在这里，我们把这个巨大的飞行器固定在它的顶端，让它像钟摆一样自由旋转。我们发现飞片具有稳定的下凹和上凹行为。重要的是，对于一系列背景流特性，向下和向上配置是可互换的并且共存。我们解释了这种双稳态的空气动力学起源，并将其与在其基础上振荡的倒立摆的惯性引起的稳定性进行比较。然后，我们让传单被动地通过引入一个旋转弹簧在其顶点。对于刚性弹簧，柔性减小向上稳定性，但随着刚度减小，通过拍动引起向上稳定性的新转变。最后，我们评论这些发现的生物和人造飞机的影响。
英文摘要：
We explore the rotational stability of hovering flight. Our model is motivated by an experimental pyramid-shaped object and a computational lambda-shaped analog hovering passively in oscillating airflows; both systems have been shown to maintain rotational balance during free flight. Here, we attach the lambda-shaped flyer at its apex, allowing it to rotate freely akin to a pendulum. We find that the flyer exhibits stable concave-down and concave-up behavior. Importantly, the down and up configurations are bistable and co-exist for a range of background flow properties. We explain the aerodynamic origin of this bistability and compare it to the inertia-induced stability of an inverted pendulum oscillating at its base. We then allow the flyer to flap passively by introducing a rotational spring at its apex. For stiff springs, flexibility diminishes upward stability but as stiffness decreases, a new transition to upward stability is induced by flapping. We conclude by commenting on the implications of these findings for biological and man-made aircraft.
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