小型无人飞行器是当前民用航空增长较快的领域之一，该类飞行器由于其特殊布局及操作形式，机翼及螺旋桨可能出现中低雷诺数翼型失速的流动现象。相较于小攻角附着流动，大攻角翼型失速将导致升力急剧减小以及噪声增大。只有突破传统附着流线升力的概念，理解大攻角失速复杂流动机理，才能扩展升力体可用攻角，更好满足工程需要。本项目以翼型大攻角失速为研究对象，通过对翼型大攻角条件下前缘剪切层、后缘脱落涡、中间二次涡的速度场测量，采用时间-空间-模态相互关联研究补充与发展过去对于局部点流动测量的结论。将传统基于麦克风的“听噪声”方法与当前流行的基于速度场测量的“看噪声”方法结合起来，在频域与时间域对流场与声场进行关联分析，从中分析噪声产生的流动机理。在攻角、雷诺数、来流湍流度这三个常见无人机工况变化的条件下，测量流动频率特征、流动模态特征、以及噪声窄频特征的变化趋势，为工程实践提供理论指导。

Airfoil stall of wings and propellers at low to moderate Reynolds numbers may occur on unmanned aerial vehicles (UAVs) because of special configurations and operation conditions of UAVs, which grow fast in civil aeronautical engineering. Compared with an airfoil which is operated a low angle of attack, the operation at a high angle of attack would lead to significant drop of lift and noise increase. For the application of lifting surfaces being operated at high angle of attack, the lift theory of attached flow is not enough and the complex flow at high angle of attack must be investigated. This project focuses on airfoil stall at high angle of attack by investigating shear flow at leading and trailing edges, separation vortex at the trailing edge, and secondary vortex at the centre chord. Spatial-temporal-modal analysis is applied for the development of airfoil stall mechanism, which was conducted by probing individual points in the flow by previous researchers. 'Seeing noise' is implemented upon the traditional 'hearing noise' method, which is significant for the noise source investigation. Aeroacoustic mechanism of airfoil stall is investigated by correlation analysis in the time and frequency domains. By tuning the parameters of angle of attack, Reynolds number and turbulence level, the flow spectra, the mode characteristics, and the narrow band of noise are analysed, which are useful for UAV engineering.