Sane Sanjay P, Jacobson Nathaniel P
Department of Biology, University of Washington, Seattle, WA 98195, USA.
J Exp Biol. 2006 Jan;209(Pt 1):43-56. doi: 10.1242/jeb.01958.
The flapping wings of insects and birds induce a strong flow over their body during flight. Although this flow influences the sensory biology and physiology of a flying animal, there are very little data on the characteristics of this self-generated flow field or its biological consequences. A model proposed in the companion paper estimated the induced flow over flying insects. In this study, we used a pair of hot wire anemometers to measure this flow at two locations near the body of a tethered flapping hawk moth, Manduca sexta. The axial inflow anemometer measured the airflow prior to its entry into the stroke plane, whereas the radial outflow anemometer measured the airflow after it crossed the stroke plane. The high temporal resolution of the hot wire anemometers allowed us to measure not only the mean induced flow but also subtle higher frequency disturbances occurring at 1-4 times the wing beat frequency. These data provide evidence for the predictions of a mathematical model proposed in the companion paper. Specifically, the absolute value of the measured induced flow matches the estimate of the model. Also, as predicted by the model, the induced flow varies linearly with wing beat frequency. Our experiments also show that wing flexion contributes significantly to the observed higher frequency disturbances. Thus, the hot wire anemometry technique provides a useful means to quantify the aerodynamic signature of wing flexion. The phasic and tonic components of induced flow influence several physiological processes such as convective heat loss and gas exchange in endothermic insects, as well as alter the nature of mechanosensory and olfactory stimuli to the sensory organs of a flying insect.
昆虫和鸟类扇动翅膀在飞行过程中会在其身体上方产生强烈气流。尽管这种气流会影响飞行中动物的感官生物学和生理学，但关于这种自我产生的流场特性或其生物学后果的数据却非常少。在配套论文中提出的一个模型估算了飞行昆虫上方的诱导气流。在本研究中，我们使用一对热线风速仪在一只被拴住的正在扑动翅膀的烟草天蛾（Manduca sexta）身体附近的两个位置测量这种气流。轴向流入风速仪测量气流进入冲程平面之前的气流，而径向流出风速仪测量气流穿过冲程平面之后的气流。热线风速仪的高时间分辨率使我们不仅能够测量平均诱导气流，还能测量以翅膀拍动频率的1至4倍出现的细微高频扰动。这些数据为配套论文中提出的数学模型的预测提供了证据。具体而言，测量到的诱导气流的绝对值与模型的估算值相符。此外，正如模型所预测的，诱导气流随翅膀拍动频率呈线性变化。我们的实验还表明，翅膀弯曲对观察到的高频扰动有显著贡献。因此，热线风速测量技术为量化翅膀弯曲的空气动力学特征提供了一种有用的方法。诱导气流的相位和持续成分会影响多个生理过程，如吸热昆虫的对流热损失和气体交换，同时也会改变对飞行昆虫感觉器官的机械感觉和嗅觉刺激的性质。
