农用无人机药箱防晃内腔结构优化设计

针对农用无人机易受药液晃动造成失稳的问题,分别采用水平阻尼格栅和竖直阻尼格栅对药箱的内腔结构进行优化设计.以激励方向液体重心相对箱体的位移幅值和液体对箱体侧壁的冲击力为评价标准,采用Fluent软件中的流体体积(volume of fluid,VOF)多相流及非稳态k-epsilon湍流模型对无人机侧向急停激励下,10％、30％、50％、70％和90％的充液率,格栅布置高度为箱体高度的30％、50％和70％,采用不同槽数的水平和竖直阻尼格栅的防晃效果进行了仿真.仿真结果表明,2种阻尼格栅都减小了晃动液体在激励方向的重心变化.在液体对箱体冲击力方面,当液面高度和布置位置重合时水平阻尼格栅会造成液体对箱体的冲击力分别增加34.4％、24.5％和15.1％,其余位置的水平格栅可以减小液体对箱体的冲击力,并在槽数为6时趋于稳定;竖直阻尼格栅使30％、50％和70％充液率下液体对药箱的冲击力降低了42.6％、51.1％和61.7％,并在格栅槽数为9时趋于稳定.据此,选取在30％和70％的药箱高度位置布置6槽的水平阻尼格栅以及9槽竖直格栅作为最终药箱的内腔结构,并制作了实物进行台架试验,试验结果与软件仿真结果相符,优化改进后的药箱对液体的晃动有较好的抑制作用.

Optimal design of anti sway inner cavity structure of agricultural UAV pesticide tank

Abstract: Aiming at the problem of agricultural UAV (unmanned aerial vehicle) instability caused by the shaking of liquid in the pesticide tank, the tank was optimally designed by arranging horizontal and vertical grille in the empty tank. The grilles were mainly to increase damping, thereby weakening the vibration of the liquid. The horizontal grille contained a number of gaps ranging from 0 to 7, and the vertical grille contained a number of gaps ranging from 0 to 10. The displacement amplitude of the liquid center relative to the tank in the excitation direction and the impact force of liquid on the side walls of the tank were taken as the evaluation conditions. At 0-0.55 s, the acceleration of the uniformly accelerated rectilinear motion was 2 m/s2, the speed remained constant at 0.55-1.1 s, and at 1.10 s, the speed was reduced to 0. The simulation condition was to simulate the acceleration and rapid stop of the UAV. The VOF (volume of fluid) model and k-epsilon model in Fluent software were used to simulate the anti sway effect of horizontal and vertical damping grille with 10%, 30%, 50%, 70% and 90% liquid filling rate, 30%, 50%, 70% arranged height and different shapes. The simulation results showed that the peak value of the liquid velocity at the vertical direction in the rectangular empty box appeared in the area near the wall of the box, and the peak value of the liquid velocity in the excitation direction appeared in the central area of the box; and 2 kinds of damping grilles both reduced the variation of the gravity center of the sloshing liquid in the excitation direction. In the case of liquid impact on the tank, the horizontal damping grille would increase the liquid impact on the tank when the depth of liquid filling and the arrangement of horizontal grille overlapped, in other cases, the horizontal grille could reduce the impact force of the liquid to the tank, and the impact force tended to be stable when the slot number was 6. The vertical damping grille could effectively reduce the impact force of the liquid to the tank under every condition of the liquid filling rate, and the impact force would be stable when the number of the grooves was 9. In order to verify the reliability of the simulation analysis, the liquid sloshing test platform was designed. The rail length of the testing platform is 1.2 m, and a three-phase AC (alternating current) motor is used to drive the liquid box. A color high-speed camera with 1 000 fps was used to collect sequential images of the liquid in the box. According to the simulation result, a tank with double horizontal grille and vertical grille was made and a bench test was carried out. An empty box and an optimized box were contrasted in the test, and both boxes were tested at 10%, 30%, 50%, 70% and 90% liquid filling depth. The tests were conducted with 10 repetitions. The test result was in agreement with the simulation result, which confirmed that the optimized tank had a better inhibitory effect on liquid sloshing. Compared with the empty tank, after optimization of the grilles, the sway time of the waving liquid was reduced significantly. The optimized box can play a better effect of calming down the waving liquid. The result will be helpful for enhancing the stability of the UAV in case of emergency braking of hitting by the wind.