[论文解读] A computational study of the aerodynamic forces and power requirements of dragonfly Aeschna juncea hovering

Mao Sun, Shi Long Lan|ArXiv.org|Apr 8, 2004

Biomimetic flight and propulsion mechanisms参考文献 21被引用 13

一句话总结

本计算研究通过在结构化网格上进行的Navier-Stokes模拟，探究了蜻蜓Aeschna juncea在悬停飞行期间的非定常气动载荷与功率需求。结果表明，阻力贡献了约65%的垂直力，每次下拍过程中产生的涡流脱落产生强烈的向上力，且由于非定常流效应，单位体重功率达到37 W kg⁻¹。

ABSTRACT

Aerodynamic force generation and mechanical power requirements of a dragonfly (Aeschna juncea) in hovering flight are studied. The method of numerically solving the Navier-Stokes equations in moving overset grids is used. There are two large vertical force peaks in one flapping cycle. One is in the first half of the cycle, which is mainly due to the hindwings in their downstroke; the other is in the second half of the cycle, which is mainly due to the forewings in their downstroke. Hovering with a large stroke plane angle, the dragonfly uses drag as a major source for its weight supporting force (approximately 65% of the total vertical force is contributed by the drag and 35% by the lift of the wings). The vertical force coefficient of a wing is twice as large as the quasi-steady value. The interaction between the fore- and hindwings is not very strong and is detrimental to the vertical force generation. Compared with the case of a single wing in the same motion, the interaction effect reduces the vertical forces on the fore- and hindwings by 14% and 16% of that of the corresponding single wing, respectively. The large vertical force is due to the unsteady flow effects. The mechanism of the unsteady force is that in each downstroke of the hindwing or the forewing, a new vortex ring containing downward momentum is generated, giving an upward force. The body-mass-specific power is 37 W kg-1, which is mainly contributed by the aerodynamic power.

研究动机与目标

• 理解Aeschna juncea实现有效悬停的非定常气动机制。
• 量化升力与阻力在悬停期间垂直力产生中的贡献。
• 评估前翅与后翅相互作用对力产生与功率效率的影响。
• 确定在非定常流条件下单位体重的机械功率需求。

提出的方法

• 在结构化（Chimera）网格上数值求解不可压Navier-Stokes方程，以处理复杂的机翼-机体运动。
• 模拟完整的拍打周期，采用模仿实际蜻蜓运动的预设机翼运动学。
• 采用动态结构化网格精确追踪运动机翼表面与演化流场。
• 基于压力与速度场计算时序解析的气动力与功率。
• 对比双翅构型与孤立单翅情况，量化相互作用效应。
• 分析涡结构与动量传递，以解释非定常力产生机制。

实验结果

研究问题

• RQ1 在Aeschna juncea悬停期间，升力与阻力对垂直力产生的相对贡献是什么？
• RQ2 非定常流效应（如涡流脱落）如何促进蜻蜓悬停中的力产生？
• RQ3 单位体重的机械功率需求是多少？其在气动与其他分量之间的分布如何？
• RQ4 前翅与后翅的相互作用如何影响整体力产生与效率？
• RQ5 为何垂直力系数显著高于准定常预测值？

主要发现

• 阻力贡献了总垂直力的约65%，升力占剩余的35%，表明阻力在支撑体重中起主导作用。
• 由于非定常流效应，特别是涡流形成，垂直力系数是准定常值的两倍。
• 每次下拍均产生一个新的涡环，携带向下的动量，从而在机翼上产生向上的气动载荷。
• 前翅与后翅的相互作用使前翅的垂直力减少14%，后翅减少16%，相比孤立机翼情况。
• 单位体重功率为37 W kg⁻¹，其中气动功率为主要组成部分。
• 较大的桨叶平面角（高迎角）增强了阻力主导的力产生，使蜻蜓即使在低展弦比机翼下也能实现有效悬停。