Data from: A new low-turbulence wind tunnel for animal and small vehicle flight experiments

Our understanding of animal flight benefits greatly from specialized wind tunnels designed for flying animals. Existing facilities can simulate laminar flow during straight, ascending and descending flight, as well as at different altitudes. However, the atmosphere in which animals fly is even more complex. Flow can be laminar and quiet at high altitudes but highly turbulent near the ground, and gusts can rapidly change wind speed. To study flight in both laminar and turbulent environments, a multi-purpose wind tunnel for studying animal and small vehicle flight was built at Stanford University. The tunnel is closed-circuit and can produce airspeeds up to 50 m s−1 in a rectangular test section that is 1.0 m wide, 0.82 m tall and 1.73 m long. Seamless honeycomb and screens in the airline together with a carefully designed contraction reduce centreline turbulence intensities to less than or equal to 0.030% at all operating speeds. A large diameter fan and specialized acoustic treatment allow the tunnel to operate at low noise levels of 76.4 dB at 20 m s−1. To simulate high turbulence, an active turbulence grid can increase turbulence intensities up to 45%. Finally, an open jet configuration enables stereo high-speed fluoroscopy for studying musculoskeletal control in turbulent flow.

我们对动物飞行的认知，极大得益于专为飞行动物设计的风洞（wind tunnel）。现有风洞设施可模拟直线、爬升、俯冲飞行状态下的层流（laminar flow），同时支持不同海拔高度的模拟环境。但动物实际飞行所处的大气环境要复杂得多：高空气流可保持层流且较为平稳，但近地面气流往往湍流极强，且阵风会快速改变风速。为了研究层流与湍流环境中的动物飞行，斯坦福大学搭建了一座可用于研究动物与小型飞行器飞行的多功能风洞。该风洞为闭环式结构，在尺寸为1.0米宽、0.82米高、1.73米长的矩形试验段（test section）中，可产生最高达50米每秒的气流速度。风道内的无缝蜂窝结构与整流筛网，配合精心设计的收缩段，可将所有运行工况下的中心线湍流强度（centreline turbulence intensities）降至0.030%及以下。配备大直径风扇与专业声学处理（acoustic treatment）的该风洞，在气流速度为20米每秒时，噪声水平可低至76.4分贝。为模拟强湍流环境，该风洞搭载的主动湍流格栅（active turbulence grid）可将湍流强度提升至最高45%。此外，该风洞采用开放式射流配置，可支持立体高速透视成像（stereo high-speed fluoroscopy），用于研究湍流环境下动物的肌肉骨骼控制（musculoskeletal control）机制。