高速气流条件下标准扇形喷头和空气诱导喷头雾化特性

标准扇形喷头与空气诱导喷头均为地面喷雾常用喷头,其在低速条件下的雾化特性已有较多研究,而在高速气流下的雾化特性尚不清楚。为了探究对比2种喷头在高速气流条件下的雾化特性,以及其用作航空喷头的可能性,基于北京农业智能装备技术研究中心自行设计制造的IEA-I型高速风洞,采用马尔文Spraytec喷雾粒度仪对德国Lechler公司生产的LU-120-03标准扇形压力喷头和IDK-120-03空气诱导喷头进行了测试。试验结果表明,两种类型喷头在距离出口0.15 m时,雾滴并未完全雾化。而在距离出口0.35 m时雾滴均已充分雾化。其中LU-120-03扇形压力喷头雾滴体积中径随风速增大从210μm逐渐减小至130μm,在管道压力达0.4 MPa以上时,其雾滴粒径分布跨度随风速增大逐渐从1.3增至1.5。而IDK-120-03空气诱导喷头产生的雾滴粒径相对较大,在风速为120 km/h时,达420~450μm,但其随着风速进一步增加快速减小,在风速达305 km/h时,其产生的雾滴体积中径降低到150μm。试验还发现管道压力变化对LU-120-03扇形压力喷头产生雾滴体积中径影响较大,而对IDK-120-03空气诱导喷头产生的雾滴体积中径影响较小。该研究可为固定翼有人机航空施药方案,如喷头选型、压力选择、作业速度选择等提供试验数据指导。

Atomization characteristics of normal flat fan nozzle and air induction nozzle under high speed airflow conditions

Flat fan nozzles and air induction nozzles are often used in ground spraying. Although the atomization characteristics of these 2 kinds of nozzles in low speed flow were studied sufficiently, their high speed atomization characteristics were still not very clear. The objectives of this research were to assess the atomization characteristics of the LU-120-03 normal flat fan nozzle and the IDK-120-03 air induction nozzle, and their suitability in agricultural aerial spray application. The experiment was conducted in the IEA-I high speed wind tunnel at National Engineering Research Center of Intelligent Equipment for Agriculture (NERCIEA) with Marvern Spraytec laser diffraction system. The measurement point was set at 0.15, 0.25 and 0.35 m away from the orifice of the nozzle which was 0.1 m outside the exit of the tunnel. The wind speed range was from 121.7 to 305.5 km/h, and the tube pressure was set to be 0.3, 0.4 and 0.5 MPa. The nozzle was installed on an electric lifting platform which could be traversed vertically so that the entire spray plume could be sampled by the laser diffraction system. Three replications for each nozzle/pressure tested were taken, and the standard deviation of volume middle diameter of droplets was required to be less than or equal to 5% of the mean. The results of the experiment to the LU-120-03 nozzle showed that when the wind speed increased from 150 to 305 km/h, the volume middle diameter of the droplets decreased from 210 to 130μm. The relative span of the droplets was found to slightly increase from 1.3 to 1.5 with the increase of the wind speed when the tube pressure exceeded 0.4 MPa. The volume middle diameter of the dropletswas also found to be related to the tube pressure. When the wind speed was less than 250 km/h, the increase of the tube pressure could decrease the volume middle diameterof the droplets. However, it would increase the volume middle diameterslightly when the wind speed exceeded 280 km/h. The main reasons of the droplet atomization were also discussed, and the aerodynamic shear stress was believed to be one of the most important reasons. Droplets generated by the IDK-120-03 nozzle had a different behavior. The volume middle diameterof the droplets decreased rapidly (by about 70%) when the wind speed increased from 120 to 305 km/h. Meanwhile, it was not affected by the tube pressure. The relative span of the droplets was mainly affected by the wind speed. When the wind speed was less than 220 km/h, the relative span of the droplets was in proportion to the wind speed. When the wind speed exceeded 220 km/h, the relative span of the droplets decreased slightly with the increase of the wind speed. The increase of the tube pressure could also increase the relative span of the droplets slightly. The measuring distance from the orifice of the nozzle was also found to be important to the diameter and relative span of the droplets. In our results, 0.35 m away from the orifice of the nozzle was a proper measuring point, at which the droplets were fully atomized.