宽喷幅风送式喷雾机空间气流速度分布规律

为了研究宽喷幅风送式喷雾机外部空间气流的分布，以期为优化其设计提供技术依据。该文对自制的宽喷幅风送式喷雾机样机外部气流速度场进行了测试，应用自由紊动射流理论对试验数据进行分析，获得了气流速度场的分布规律与变化机理。结果表明：风机在不同供电频率44、46、48、50 Hz时，宽喷幅风送式喷雾机轴心上的纵向时均风速随送风距离的变化均呈幂函数变化规律，气流中心速度符合三维自由紊动射流纵向中心速度幂函数衰减规律；宽喷幅风送式喷雾机的喷幅与送风距离成线性关系。根据试验数据，回归了射流边界曲线，射流与地面之间的涡结构使出风口长轴方向的射流边界曲线上下不同，两射流边界线相交点的"虚源"不在水平轴线上，上下射流边界线与轴向水平线之间的夹角分别为20.5°和28.8°；同时，沿出风口短轴方向的两射流边界曲线变化规律基本相同，两射流边界线相交点的"虚源"处在水平轴线上，射流边界线与轴向水平线之间的夹角分别为4.18°和4.23°；在纵向送风距离分别为0.5、1、1.5、2和2.5 m处的断面上，气流纵向时均速度的分布沿出风口的短轴方向上分布相似、而沿长轴方向上分布不相似；气流速度场三维曲面重构后发现，沿出风口的长轴方向上，在外边界层的内侧，风速的分布出现2个高风速区。

Law of spatial airflow velocity distribution for wide-swath air-blast sprayer

Abstract: Spraying droplet adhesion and deposition were affected by the external flow field distribution of the air-blast sprayer. The swath of an air-blast sprayer can be expanded through expanding the duct and elongating rectangular outlet. In this paper, a wide-swath air-blast sprayer was applied as the experimental platform and its external airflow velocity field was tested. The duct of the wide-swath air-blast sprayer used in the experiment was made up of a cylindrical segment, a contractive segment, and an expanding segment. An axial fan was installed inside the cylindrical segment, and there were a semi-elliptical fluid director and distributors in the contractive segment. One end of the expanding segment was connected with contractive segment and the other was a rectangle outlet. The long side of the rectangle outlet was vertical to the ground and the axis of the duct was parallel to the ground simultaneously when testing was conducted. The airflow speed field of the wide-swath air-blast sprayer was tested indoors. The airflow speed sampling points were located with a sampling frame made up of lattices (11×11cm), and the airflow speed field and spray swath were tested in cross-sections 1m, 1.5m, 2m, and 2.5m away from the outlet. The average of ten testing wind speeds at each sample point was taken as the final speed of that point. The free turbulent jet theory was applied for data analysis. The distribution and variation mechanism of the wide-swath air-blast sprayer airflow velocity were obtained. The experimental results indicated that the relationship between the axial longitudinal time-averaged wind speed and the air blast distance of the wide-swath air-blast sprayer took on an attenuated power function with the fan power supply in different frequencies. The axial longitudinal time-averaged wind speed was in line with the attenuated power function regular pattern to which the axial longitudinal speed of the three-dimensional free turbulent jet was submitted. The relationship between swath and air blast distance of the wide-swath air-blast sprayer presented a linear direction. According to the experimental data, the jet boundary curves were regressed. The top boundary curve and the bottom boundary curve of the jet along the outlet's long axis was not the same, as there was a vortex structure between the jet and the ground. The "virtual source," a point at which the top boundary and the bottom boundary intersected was not on the horizontal axis of the duct. The angle between the top boundary and the horizontal axis of the duct was 20.5°, while the angle between bottom boundary and the horizontal axis was 28.8°. Meanwhile, it was found that the two boundaries of the jet along the outlet's short axis were in keeping with the same regular pattern. The "virtual source," a point at which two boundaries intersected was on the horizontal axis of the duct, and the angles between the two boundaries and the horizontal axis of the duct were approximately 4.18° and 4.23° respectively. At cross-sections 0.5m, 1m, 1.5m, 2m, and 2.5m distances away from the duct outlet, the distributions along the outlet's short axis direction of the axial wind speed were similar. However, the distributions were not similar along the long axis direction. After a three-dimensional surface of airflow velocity field was reconstructed, two peaks of wind speed appeared along the long axis direction inside the boundary layer.