Effect of Wind Field below Rotor on Distribution of Aerial Spraying Droplet Deposition by Using Multi-rotor UAV

Abstract

Currently, studies about aerial spraying application of agricultural unmanned aerial vehicle (UAV) in China mainly focus on the effect of aerial spraying operation parameters (flight height and flight velocity) of single-rotor UAV on droplet deposition distribution. In fact, the main factor that affects the droplet deposition distribution of aerial spraying is the wind field below the UAV rotor, which is made up of wind field generated by rotating rotor and wind field of external environment. The effect of wind field below agricultural UAV rotor needs to be taken into account in the study of the distribution regularity of aerial spraying droplet deposition. Moreover, the wind field generated by multi-rotor electric UAV during operation is the result of multiple rotor interaction. The distribution of wind field and the effect of wind field on the distribution regularity of droplet deposition are different with single-rotor UAV. In order to reveal the impact mechanism of droplet deposition distribution by the wind field below the multi-rotor electric UAV rotor, wind field distribution below multi-rotor electric UAV was measured by using a wireless wind speed sensor network measurement system for unmanned helicopter, and the impact on the distribution of droplet deposition was analyzed by the wind field in X, Y and Z directions below rotor combined with the condition of aerial spraying droplets deposition in rice canopy, and the regression model was established by making the variance analysis and regression analysis of experiment results. The results showed that the trends of droplet deposition in the plant layers were basically similar, the deposition amount of droplet was decreased from upper layer to lower layer. Because of the different operating parameters, the distribution of wind field below rotor in each experiment were different, but the value of wind speed in different directions showed the decreasing trend in Z, Y and X directions. Among the three directions wind field below multi rotor electric UAV rotor, the wind field in X and Y directions had no significant impact on droplet deposition in the effective spray area, the wind field in Z direction had an extremely significant impact on droplet deposition in the effective spray area, the Sig. value was less than 0.001. The wind field in X direction had no significant impact on droplet deposition penetration in the effective spray area, the wind field in Y direction had a significant impact and the wind field in Z direction had an extremely significant impact on droplet deposition penetration in the effective spray area, the corresponding Sig. values were 0.037 and less than 0.001. The wind field in X and Y directions had no significant impact on droplet drift, the wind field in Z direction had a significant impact on droplet drift, the Sig. value was 0.036. Furthermore, the horizontal wind field in X and Y directions and the vertical wind field in Z direction all affected the deposition uniformity in the effective spray area. With the smaller value of horizontal wind field in X and Y directions and the larger value of vertical wind field in Z direction, the uniformity of droplet deposition was better, the best value reached 36.44%. In addition, the corresponding determination coefficient R2 of the regression model between droplet deposition in effective spray area and the wind speed in Z direction as well as between droplet deposition penetration in effective spray area and the wind speed in Y and Z directions were 0.868 and 0.842, respectively, and these models can provide guidance for the practical application. The result revealed the effect on the distribution of aviation spraying droplet deposition by the wind field below the multi-rotor UAV rotor, and it had an important guiding significance in the practical application such as reducing liquid drift in aerial spraying and improving the utilization rate of pesticide.

Keywords: multi-rotor UAV, wind field below rotor, droplet deposition