Abstract Unmanned helicopters are used widely in precision agriculture, especially in East Asia. However, the development of the downwash flow field of unmanned helicopters, which strongly influences the movement of spray droplets in the air, is poorly understood. Therefore, an indoor measurement technique was developed to investigate the downwash flow field of a 1:10 scaled unmanned agricultural helicopter (AF-25B; Copterworks). High-speed particle image velocimetry was employed to obtain the instantaneous and average velocity field of the downwash flow, with a spatial resolution less than 0.005 m and temporal resolution less than 0.001 s. Results showed that radial distance of the point at which downwash flow reached the ground was proportional to the hovering height of the helicopter at a hovering height of z/R

中文翻译：

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用于精准农业的无人直升机的高精度、高分辨率下洗流场测量

摘要 无人直升机广泛应用于精准农业，尤其是在东亚地区。然而，无人直升机的下洗流场的发展对空气中喷雾液滴的运动产生强烈影响，却知之甚少。因此，开发了一种室内测量技术来研究 1:10 比例的无人驾驶农用直升机（AF-25B；Copterworks）的下洗流场。采用高速粒子图像测速仪获取下洗流的瞬时和平均速度场，空间分辨率小于0.005 m，时间分辨率小于0.001 s。结果表明，下洗气流到达地面点的径向距离与直升机在z/R的悬停高度上的悬停高度成正比。