相邻喷头射流相互作用对喷洒特性的影响

Effect of jets interaction on spray characteristics between adjacent sprinklers

相邻喷头喷洒重叠区域内的射流来自不同喷头,喷射过程中往往产生冲撞等相互作用。为研究组合喷头喷洒过程中相邻喷头间射流相互作用对组合喷洒特性造成的影响,选取Nelson D3000锯齿状喷盘喷头和R3000旋转式喷头,对其单独喷洒和以2.5 m组合间距进行喷洒时的水量分布以及雨滴谱信息进行了测试与比较。结果表明:喷头之间相互影响的强弱程度受喷头几何结构的影响,R3000喷头受组合喷洒时喷头间射流的影响作用不明显;Nelson D3000喷头(锯齿状喷盘)受组合喷洒时喷头间射流的影响作用剧烈,水量分布集中点的位置因射流轨迹的变化而产生偏移,喷灌强度最大点向靠近喷头侧偏移约0.5 m。组合喷洒条件下测点MP5处的降水强度、能量通量密度以及水滴数目较单独射流分别增长91.27%、107.58%和239.29%,其中粒径大于0.9 mm水滴数目的增加对该测点水量和能量提升的贡献率达到40.89%和58.83%。变异性分析结果表明水量和能量的重分布主要是由组合喷洒时增加了水滴之间相互碰撞的机率所引起。在Nelson D3000锯齿状喷盘喷头这类喷头进行水量叠加计算时,应考虑相邻喷头间水滴互相碰撞、结合或碎裂等相互作用对组合后的水量分布形式产生的影响,采用单喷头水量分布直接叠加的方法可能会导致计算精度较低。

Spray jets in the overlap region of adjacent sprinklers come from different applicators. Collisions and other interactions in the injection process are inevitable. However, the water distribution of a single sprinkler nozzle is always used to calculate the combination of sprinkler irrigation uniformity by giving an overlapping space due to the limitations of test site, sprinklers layout or other conditions. To study the effect of jets interaction on the overlapped spray characteristics between adjacent sprinklers, two different types of sprinklers were selected, namely, Nelson D3000 sprinkler with coarse jagged plate and Nelson R3000 rotating spray plate sprinkler. Water distribution pattern and droplets spectrum were measured and compared with the two nozzles spraying separately and simultaneously, with a combinatorial space of 2.5 m. The water distribution and raindrop spectrum of separately sprinkling were added together as theoretical combination （TC） while the simultaneously sprinkling was named actual superposition （AS）. The results showed that the strength of interaction between sprinklers was influenced by geometry structure of nozzle. The influence of jets interaction on Nelson R3000 rotating spray plate sprinkler was not significant. In contrast, Nelson D3000 sprinkler with coarse jagged plate was severely affected by the effect of jets interaction, and the water application rate and kinetic energy had obvious redistribution along the radial direction. The location of precipitation concentrated points had an offset due to the change of jets trajectories and the point with maximum precipitation intensity moved 0.5 m closer to the sprinkler nozzle. At the measuring point of 2.5 m, the application rate, energy flux density and droplet number of AS increased by 91.27%, 107.58% and 239.29% when compared with TC. The increase of the number of droplet size grater than 0.9 mm showed great contribution to the water and energy rise at this measuring point, and the contribution rate reached 40.89% and 58.83%, respectively. Both the drop landing velocity and landing angle under AS condition were lower than that under TC condition. Under TC condition, the largest drop landing velocity and landing angle were 6.01 m/sand 75.38o while the values changed into 4.59 m/s and 63.91ounder the condition of AS. The droplets spectrum variability analysis of the overlapping region reflected that the redistribution of water application rate and kinetic energy was mainly due to the increasing probability of droplets collision when multi-sprinklers were spaced for irrigation. Water droplets changed original trajectories by the effect of external forces, and interacted with other droplets to form bigger size of drop or dispersed into a large number of tiny droplets. The strength of jets interaction should be considered when calculating the overlapped water application rate with a relatively small space, a direct superposition of single sprinkler water distribution might cause distortion of the results. This study on spraying hydraulic performance tests were carried out in fixed nozzle under indoor conditions, and further studies on multiple nozzles under mobile condition are needed to determine the impact of jet interaction on the spray characteristics.