N-3型农用无人直升机航空施药飘移模拟与试验

为了判定N-3型农用无人直升机在进行病虫害防治作业时所需的安全农药飘移缓冲区,该文通过模拟和试验,研究了飞机在飞行速度为3 m/s、侧风风速分别为1、2和3 m/s、飞行高度为5、6和7 m时在非靶标区域的药液飘移情况。采用计算流体力学(computational fluid dynamics,CFD)方法,在约束条件下对作业过程中旋翼风场和农药喷洒的两相流进行了模拟,并设计了条件相似的对应试验进行验证。模拟的结果表明,在无人机飞行速度3 m/s,侧风风速相同的情况下,作业飞行高度为5、6、7 m时,药液在侧风下方(Z轴正向)的最大飘移距离和在无人直升机后方(X轴负向)的最大沉积量位置差异不大;在作业飞行高度相同的情况下,侧风风速为1、2、3 m/s时候,药液在侧风下方的最大飘移距离和在无人直升机后方的最大沉积量位置发生变化明显。通过相应试验,对飘移量(飞行高度6 m,飞行速度3 m/s)的模拟数值与试验值的变化趋势进行了比较,并进行线性回归分析,拟合直线决定系数R2分别为0.7482、0.8050和0.6875。本文提出一种较传统检测方法更为方便的CFD模拟方法,来对N-3型无人直升机施药作业中药液的飘移情况进行分析,模拟研究可以比较准确地定性地模拟出实际飘移情况,对实际生产具有一定的指导意义。

Simulation and experimental verification of aerial spraying drift on N-3 unmanned spraying helicopter

Abstract: In order to find out the safe buffer areas of pesticide drift during the aerial spraying by N-3 unmanned aerial vehicle (N-3 UAV), researches on pesticide drift were done, by simulations and experiments as flight speed was 3 m/s, crosswind velocities were 1m/s, 2m/s and 3m/s, flight heights were 5 m, 6 m and 7 m. According to the parameters of the N-3 UAV and the aerial spraying operations, the whole equipment, atomizing surface and the entire computational domain were grid-processed first. A turbulence model by means of approximate solutions of N-S equations with appropriate boundary condition was developed and the two-phase flow of rotor wind field and pesticide-spraying was simulated. In the simulations, the equations were discretized by second-order upwind format based on the finite volume methods, the fluxes were calculated by the ROE scheme. Iterative calculations were processed using Gauss - Seidel method to analyze the droplets flow rate changes under the wind generated by the UAV's rotor until to the flow stability when the calculation converges residuals dropped more than three orders of magnitude, then liquid concentration and density of each grid were achieved, resulting droplet drift and deposition. And the model was verified by experiments. A solution of tracer (Rhodamine-B) mixed with water in a certain concentration was selected to replace the pesticide for aerial spraying, to monitor the wind velocity as well as the temperature and humidity. The N-3 UAV flight heights were changed in the experiments. The target area was a rectangle by 50 m×20 m, and the fly route was the centerline. Mylar cards with a diameter of 90 mm every 2 m downwind, 5 m along the flight direction out of the target area were sampled to collect the droplets drifted, forming a 50m×10m drift sample area. The drift amount at each sampling position was measured by means of a fluorescence spectrophotometer to obtain the regularities of droplets drifted by the wind. The simulations showed that the drift distance downwind (along positive Z-axis) and the maximum amount of drift position rear the UAV (along negative X-axis) were not significant with 5 m, 6 m, 7 m flight height under the same crosswind velocity, while which were relatively significant as crosswind velocity changed from 1 m/s to 3 m/s with the same flight height. The comparison results of amounts and trends of droplet drift (when flight height was 6 m, crosswind velocity was 1 m/s, 2 m/s, 3 m/s) showed that the simulated and measured curves were coincident, and the correlation determination (R2) were 0.7068, 0.8451 and 0.6859 respectively, which showed that the research had a significance for determining the buffers before aerial spraying to insure the safety. Also, the following conclusions can be drawn by the simulation and experiment results: the crosswind velocity is greater than the aerial spraying height as the droplet drift affecting factors; the droplet drift only occurs downwind of the spraying field, and as the crosswind velocity is 1-3 m, 8-10 m buffer zones should be considered downwind the spraying field for safe aerial spraying.