温室环境中靶标周围流场对雾滴附着行为的影响

发布时间：2018-03-18 08:41

本文选题：沉积分布　切入点：雾滴轨迹　出处：《中国农业大学》2016年博士论文　论文类型：学位论文

【摘要】：在温室环境中用气流辅助方式喷施农药时,雾滴在气流胁迫下的飞行轨迹与附着行为受到气流速度场、压力场、雾滴物理性质(如粒径、初始速度等)、喷雾角度及靶标具体参数(如形状、大小、位置等)等条件的影响。本文主要探讨在温室环境中用气流辅助方式喷施农药时,施药对象(靶标)周围的流场对雾滴飞行轨迹及雾滴附着行为所产生的影响。本文使用数值模拟研究雾滴速度、雾滴粒径以及喷雾角度对雾滴沉积率的影响,并通过试验手段验证了模拟结果的可靠性。计算域为长1600mm,宽720mm,高1000mm的空间。为便于建模,将植株简化为高于地面400mm距离左边界840mm的120mmx 120mmx30mm的长方体靶标。通过本文的工作,我们可以得到以下结论：1)以雾滴粒径为50μm,喷雾角度为60°的流场分析雾滴的沉积条件。在靶标附近区域,对区域内的雾滴轨迹进行分析后发现,雾滴在3个方向实现附着的最大可能时间必须同时满足x方向的最大可能运行时间和y方向的最大可能运行时间均大于z方向的运行时间,才能实现对靶标的附着;2)粒子粒径分别设置为10μm、30μm、40μm、50μm、60μm、70μm、80μm和100μm,喷雾角度分别设置为75°、60°、45°、30°和15°,计算不同条件下粒子附着靶标的沉积率。增大粒径与增大喷雾角度都有助于获得较高的雾滴的沉积率,但是当雾滴粒径较小时,增大喷雾角度并不能获得明显的沉积率增加的效果。而当雾滴粒径较大时,增大喷雾角度会显著增加雾滴的沉积率；3)喷雾角度设置为75°、60°、45°、30°和15°,对比40μm与80μm粒径雾滴的运动轨迹。雾滴沉积与否与流场中的压力分布以及雾滴初始位置有关。在同样的压力场条件下,雾滴粒径大的更容易沉积。因为在靶标上表面的高压区对空气存在加速作用,推动靶标上表面的空气流向靶标边缘,粒径较大的雾滴的随流性较差,对空气的加速过程不敏感,所以能够实现沉积;4)喷雾角度设置为75°45°和150。喷雾过程中靶标下方存在雾滴不能到达的遮挡区域,靶标对雾滴运动的遮挡长度与喷雾角度有关。在喷雾角度小于45°时,靶标的遮挡长度受喷雾角度的影响较大,其大小随着角度的增加而增大。而当喷雾角度大于45°时,靶标的遮挡长度受喷雾角度的影响较小;5)喷雾角度设置为60°,气流速度则选取0.5m/s到3.0 m/s之间且间隔为0.25 m/s的11个速度条件来研究各进口速度条件下靶标对雾滴沉积的影响。当采用不同喷雾速度时,雾滴在靶标上表面的沉积率受到靶标附近的压力场及速度场的影响很大。当雾滴粒径为50μm,喷雾角度为60°时,随着喷雾速度的增加,雾滴的沉积率下降。
[Abstract]:When pesticide was sprayed in greenhouse by airflow aid, the flight path and adhesion behavior of droplets under airflow stress were subjected to airflow velocity field, pressure field, droplet physical properties (such as particle size, etc.). The effects of initial velocity, spray angle and target parameters (such as shape, size, position, etc.) are discussed in this paper. The effect of the flow field around the target on the droplet flight path and the droplet adhesion behavior was studied in this paper. The effects of droplet velocity, droplet diameter and spray angle on droplet deposition rate were studied by numerical simulation. The reliability of the simulation results is verified by experimental means. The calculation field is 1600mm in length, 720mm in width and 1000mm in height. In order to model the model, the plantlet is simplified as a cuboid target of 120mm x 120mmx30mm above the left boundary of 400mm above the ground. We can get the following conclusion: 1) the deposition conditions of droplets are analyzed in the flow field of 50 渭 m droplet size and 60 掳spray angle. In the area near the target, the droplet trajectories in the region are analyzed. The maximum possible time for fog droplets to achieve attachment in three directions must satisfy both the maximum possible running time in the x direction and the maximum possible running time in the y direction, which is larger than that in the z direction. The particle size was set to 10 渭 m, 30 渭 m, 40 渭 m, 50 渭 m, 60 渭 m, 70 渭 m, 80 渭 m and 100 渭 m, respectively, and the spray angle was set at 75 掳, 60 掳, 45 掳, 30 掳, and 15 掳, respectively. The deposition rate of particles attached to the target was calculated under different conditions. Increasing the particle size and increasing the spray angle were helpful to obtain the results. Higher deposition rate of droplets, However, when the droplet size is small, the effect of increasing spray angle is not obvious, but when the droplet size is larger, When the spray angle was increased, the deposition rate of droplets was significantly increased. The spray angles were set to 75 掳60 掳45 掳C 30 掳and 15 掳, comparing the motion trajectories of 40 渭 m and 80 渭 m size droplets. The deposition of droplets was related to the pressure distribution in the flow field and the initial position of droplets. Under the same pressure field, Because the high-pressure area on the surface of the target accelerates the air, and promotes the air on the surface of the target to flow to the edge of the target, the larger droplet has a poor flowability and is insensitive to the acceleration process of the air. So it can be realized that the spray angle is set to 75 掳45 掳and 150 掳. During the spray process, there is an unreachable occlusion area under the target, and the length of the fog droplet motion is related to the spray angle. When the spray angle is less than 45 掳, The occlusion length of the target is greatly affected by the spray angle, and its size increases with the increase of the angle, but when the spray angle is greater than 45 掳, The occlusion length of the target is less affected by the spray angle.) the spray angle is set to 60 掳, and the airflow velocity is determined by 11 velocity conditions between 0.5 and 3.0 m / s, with an interval of 0.25 m / s, to study the droplet deposition of the target at each inlet velocity. When different spray rates are used, The deposition rate of droplets on the surface of the target is greatly affected by the pressure field and velocity field near the target. When the droplet size is 50 渭 m and the spray angle is 60 掳, the deposition rate decreases with the increase of spray velocity.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S491

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