| In the process of agricultural production in China,agricultural aerial spraying is an important development direction of pest control.It has the advantages of high efficiency of spraying,good operation quality,good terrain adaptability,and ability to cope with sudden diseases and insect pests.It can be applied to the control of pests and diseases in a large area of concentrated planting crops.Application of plant protection UAV in China is more extensive.Due to the relatively large height of the plant protection UAV from the crop canopy and its fast flying speed.These have caused the plant protection UAV rotor downwash flow is complicated.However,the downwash flow field of plant protection UAV directly affects the quality of spraying.If the spray droplets is not evenly and drifts,it will not only affect the working efficiency of plant protection UAV,but also cause unpredictable pesticide pollution.This paper aims at solving the above problems by studying indoor model wind field,outdoor actual wind field and droplet deposition.It explores the distribution rule of rotor downwash flow field of plant protection UAV.The content and results of this study are as follows:(1)Research on measurement of downwash flow field of indoor UAV model.Based on similarity theory,the Reynolds model method was used to study the scale model of plant protection UAV.For this purpose,a DPIV measurement platform for the indoor UAV scale model wind field was built,and the measurement experiment for downwash flow field of the plant protection UAV scale model was designed.The average velocity fields of the rotor downwash flow field was obtained by experiments under the conditions of five kinds of rotor hover heights(1.0R,1.5R,2.0R,2.5R,3.0R)and three kinds of rotor speeds(1200rpm,2400 rpm,3600rpm).And through the orthogonal decomposition of the eigenvalues of the velocity field obtained by the DPIV measurement,and the identification and extraction of the typical flow structure of the flow field.At different rotational speeds,The area of influence of the wake zone directly below the model near the ground.The radius of influence is reduced from 1.0R to 0.8R,which can affect the area about 0.4R above ground.At different heights,the speed range of the downwash airflow is approximately 0.7R,and the maximum downwash speed is about 0.05 times wingtip speed.The angle with the ground increases as the height from the ground increases,and the area of the wake zone below the rotor increase as the height from the ground increases,and the radius of influence near the ground increased from 1R to about1.5R.When the hovering height is less than 2R,the flow state directly below the rotor is a largescale single vortex structure.When the hovering height is higher than 2R,the structure is splits into upper and lower layers.The upper vortex structure is a wake vortex structure caused by the flow around the fuselage,and the lower vortex structure is a secondary vortex formed by the ground reflection.In addition,three typical modes of generation of burst vortex structures that have an important effect on spray droplet transport have also been discovered.(2)Research on measurement of downwash wind field of outdoor UAV.Based on the ultrasonic wind measurement technology,a measurement platform for the rotor downwash flow field of outdoor UAV was set up.In the hovering and cruising state of the AF25 B plant protection unmanned helicopter,a measurement experiment of the downwash airflow of the rotor was carried out.According to the experimental results,when the plant protection UAV is in the hovering state,the radius of the affected area is 0.7R when the downwash airflow of the rotor is far away from the ground,and the maximum downwash speed of the rotor downwash speed field is about 6 m/s.When it is attached to the ground,its influence area radius reaches3 R,which can affect the area about 0.4R above ground,and the spanwise wind speed can reach2.5m/s.The flow structure of the downwash flow field is similar to that of the indoor model when the hover height is 2.5R.The measurement result of the hovering wind field in the outside can provide reference for the experimental results of the indoor model.When the plant protection UAV is in the cruising state,the strength of the downwash airflow of the rotor gradually decreases as the height from the ground decreases,and the strength of the flow field reaches the maximum in the region of 1.4 R from the ground,and the maximum downwash speed of the instantaneous speed field is about 6.4 m/s.(3)Research on spraying deposition law of UAV.The distribution of droplet deposition was studied based on the water sensitive paper image measurement analysis method and tape fluorescence detection analysis method,and the measurement results of the downwash airflow of the rotor were verified on the side.In the hovering and cruising state of the AF25 B plant protection unmanned helicopter,a measurement experiment of the droplet deposition distribution was carried out.According to the experimental results,the droplet deposition distribution of the plant protection UAV was obtained.When hovering at a height of 2.5R,the main deposition area of the droplets is concentrated in the elliptical region of which the long and short axes are 5R×2R.When cruising at a height of 2.5R,the spatial distribution of droplet deposition is consistent with the distribution of the downwash flow field of rotor.In the rotordownwash flow field of the plant protection UAV,the wind speed in U and V direction had no significant effect on droplet deposition in the wind field,the wind speed in W direction had an extremely significant on droplet deposition in the wind field.In addition,The best uniformity of droplet deposition is 0.5m from the ground. |
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