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High-accuracy, high-resolution downwash flow field measurements of an unmanned helicopter for precision agriculture

文献类型： 外文期刊

作者： Tang, Qing 1 ; Zhang, Ruirui 1 ; Chen, Liping 1 ; Xu, Gang 2 ; Deng, Wei 2 ; Ding, Chenchen 2 ; Xu, Min 2 ; Yi, Tongchuan 2 ;

作者机构： 1.Beijing Acad Agr & Forestry Sci, Beijing Res Ctr Intelligent Equipment Agr, Beijing 100097, Peoples R China

2.Natl Res Ctr Intelligent Equipment Agr, Beijing 100097, Peoples R China

3.Natl Ctr Int Res Agr Aerial Applicat Technol, Beijing 100097, Peoples R China

4.Beijing Acad Agr & Forestry Sci, Beijing Key Lab Intelligent Equipment Technol Agr, Beijing 100097, Peoples R China

关键词： Precision agriculture; Unmanned helicopter; Downwash flow; Particle image velocimetry; Flow structure

期刊名称：COMPUTERS AND ELECTRONICS IN AGRICULTURE （ 影响因子：5.565； 五年影响因子：5.494 ）

ISSN： 0168-1699

年卷期： 2020 年 173 卷

页码：

收录情况： SCI

摘要： 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 < 2.5 (where z is the rotor height above the ground, and R is the rotor radius), whereas the maximum radial velocity near the ground was inversely proportional to the hovering height. In addition, the spatial distribution of the turbulence kinetic energy at different hovering heights was determined. Intense fluctuations were concentrated along the outer edge of the main downwash flow and secondary vortex near the ground, which might result in more uniform droplet distribution. Based on the instantaneous analysis of the downwash flow structures, velocity profile induced by the rotor tip vortex, the moving tracks of the vortices, and decay rate were obtained. A typical burst-type flow structure in the downwash flow field was also observed, which may contribute to droplet drift. These indoor test results were comparable to previous field test results. This study offers high-accuracy indoor test data that can be used as a reference for future simulation studies.

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