果蝇大小昆虫起飞的气动地面效应
Aerodynamic ground effect in fruitfly sized insect takeoff
摘要：
扑翼昆虫飞行中的气动地面效应对比较形态学和微型飞行器（MAV）界的兴趣是重要的。然而，最近的研究表明，显然矛盾的结果，要么一些显着的额外升力或功率节省，或零地面效应。在这里，我们提出了一个数值研究果蝇大小的昆虫起飞的腿推力和翅膀运动学的意义上的具体重点。采用数值模拟和高性能计算的方法对扑翼起飞进行了研究。气动力的计算使用三维Navier-Stokes方程求解器的基础上的伪谱方法与体积惩罚。它与一个飞行动力学求解器相结合，该求解器考虑了体重、惯性和腿部推力，同时只有两个自由度：垂直和纵向水平位移。果蝇的自然自愿起飞被认为是参考。然后改变模型的参数，以探索扑翼模型和地平面之间的相互作用的可能影响。这些修改的起飞包括具有减小的腿部推力参数和/或具有周期性机翼运动学、恒定的机身俯仰角的情况。结果表明，自然起飞过程中地面效应可以忽略不计。在改进的起飞中，当爬升速率很慢时，由于与地面的相互作用而产生的气动力差异高达6%。令人惊讶的是，根据运动学，差异是正的或负的，与基于直升机理论的直觉相反，直升机理论认为是正的多余升力。这种效应归因于非定常机翼-尾流干扰。在悬停期间发现类似的效果。
英文摘要：
Aerodynamic ground effect in flapping-wing insect flight is of importance to comparative morphologies and of interest to the micro-air-vehicle (MAV) community. Recent studies, however, show apparently contradictory results of either some significant extra lift or power savings, or zero ground effect. Here we present a numerical study of fruitfly sized insect takeoff with a specific focus on the significance of leg thrust and wing kinematics. Flapping-wing takeoff is studied using numerical modelling and high performance computing. The aerodynamic forces are calculated using a three-dimensional Navier--Stokes solver based on a pseudo-spectral method with volume penalization. It is coupled with a flight dynamics solver that accounts for the body weight, inertia and the leg thrust, while only having two degrees of freedom: the vertical and the longitudinal horizontal displacement. The natural voluntary takeoff of a fruitfly is considered as reference. The parameters of the model are then varied to explore possible effects of interaction between the flapping-wing model and the ground plane. These modified takeoffs include cases with decreased leg thrust parameter, and/or with periodic wing kinematics, constant body pitch angle. The results show that the ground effect during natural voluntary takeoff is negligible. In the modified takeoffs, when the rate of climb is slow, the difference in the aerodynamic forces due to the interaction with the ground is up to 6%. Surprisingly, depending on the kinematics, the difference is either positive or negative, in contrast to the intuition based on the helicopter theory, which suggests positive excess lift. This effect is attributed to unsteady wing-wake interactions. A similar effect is found during hovering.
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