We present a detailed analysis of the voluntary take-off procedure of a dragonfly. The motions of the body and wings are recorded using two high-speed cameras at Beihang University. The experimental results show that the dragonfly becomes airborne after approximately one wingbeat and then leaves the ground. During this process, the maximum vertical acceleration could reach 20 m/s2. Evidence also shows that acceleration is generated only by the aerodynamic force induced by the flapping of wings. The dragonfly voluntary take-off procedure is divided into four phases with distinctive features. The variation in phase difference between the forewing and hindwing and angle of attack in the down-stroke are calculated to explain the different features of the four phases. In terms of the key parameters of flapping, the phase difference increases from approximately 0 to 110 degrees; the angle of attack in down-stroke reaches the maximum at first and then decreases in the following take-off procedure. Due to experimental limitations, 2-D simulations are conducted using the immersed boundary method. The results indicate that the phase difference and the angle of attack are highly correlated with the unsteady fluid field around the dragonfly’s wings and body, which determines the generation of aerodynamic forces.
展开▼
机译：我们将对蜻蜓的自愿起飞程序进行详细分析。身体和翅膀的运动是使用北京航空航天大学的两个高速摄像机记录的。实验结果表明，蜻蜓大约在一次侧翼拍打后就可以飞行，然后离开地面。在此过程中，最大垂直加速度可能达到20 m / s 2 。证据还表明，加速度仅由机翼拍打产生的空气动力产生。蜻蜓的自愿起飞程序分为四个阶段，每个阶段都有自己的特色。计算了下行程中前，后翼之间的相位差和迎角的变化，以解释这四个阶段的不同特征。就拍打的关键参数而言，相位差从大约0度增加到110度；下行程的迎角首先达到最大，然后在随后的起飞程序中减小。由于实验的局限性，使用沉浸边界方法进行了二维模拟。结果表明，相位差和迎角与蜻蜓的机翼和身体周围的不稳定流体场高度相关，这决定了空气动力的产生。
展开▼
