Data from: Smart wing rotation and trailing-edge vortices enable high frequency mosquito flight

Mosquitoes exhibit unusual wing kinematics; their long, slender wings flap at remarkably high frequencies for their size (>800 Hz)and with lower stroke amplitudes than any other insect group1. This shifts weight support away from the translation-dominated, aerodynamic mechanisms used by most insects2, as well as by helicopters and aeroplanes, towards poorly understood rotational mechanisms that occur when pitching at the end of each half-stroke. Here we report free-flight mosquito wing kinematics, solve the full Navier–Stokes equations using computational fluid dynamics with overset grids, and validate our results with in vivo flow measurements. We show that, although mosquitoes use familiar separated flow patterns, much of the aerodynamic force that supports their weight is generated in a manner unlike any previously described for a flying animal. There are three key features: leading-edge vortices (a well-known mechanism that appears to be almost ubiquitous in insect flight), trailing-edge vortices caused by a form of wake capture at stroke reversal, and rotational drag. The two new elements are largely independent of the wing velocity, instead relying on rapid changes in the pitch angle (wing rotation) at the end of each half-stroke, and they are therefore relatively immune to the shallow flapping amplitude. Moreover, these mechanisms are particularly well suited to high aspect ratio mosquito wings.

蚊子展现出非同寻常的翅膀运动学（wing kinematics）特性：其修长的翅膀相较于其他所有昆虫类群，以与其体型极不相称的高频率（超过800赫兹）拍动，且拍动幅度低于任何其他昆虫类群¹。这使得其重量支撑机制脱离了大多数昆虫²（以及直升机、固定翼飞机）所采用的、以平动主导的空气动力学原理，转而依赖于学界尚未完全阐明的、在每个半拍动末端俯仰时产生的旋转升力机制。本研究报道了自由飞行状态下蚊子的翅膀运动学数据，采用搭载重叠网格（overset grids）技术的计算流体动力学（computational fluid dynamics）方法求解完整纳维-斯托克斯方程（Navier–Stokes equations），并通过活体流动测量（in vivo flow measurements）结果对计算结果进行了验证。研究结果显示，尽管蚊子采用了昆虫飞行中常见的分离流模式（separated flow patterns），但其支撑体重的绝大部分空气动力，却以一种此前从未在飞行类动物中被报道过的方式产生。该升力机制包含三个核心特征：一是前缘涡（leading-edge vortices，这一广为人知的机制几乎普遍存在于昆虫飞行中），二是由拍动反转时的尾迹捕获（wake capture）效应引发的后缘涡，三是旋转阻力。其中两项新机制基本不依赖翼面速度，而是依靠每个半拍动末端的俯仰角（pitch angle）快速变化（即翅膀旋转），因此受较小的拍动幅度影响相对较弱。此外，这类机制尤其适配蚊子所拥有的高展弦比（aspect ratio）翅膀。