考虑配重的垂直摇臂式喷头摇臂运动规律及水力性能

Arm movement law and hydraulic performance of vertical impact sprinkler with counterweight

为了研究摇臂运动规律及配重对喷头水力性能的影响，以垂直摇臂式喷头为研究对象，对垂直摇臂式喷头摇臂的运动特征进行理论分析，推导出摇臂运动周期公式，并在公式中考虑了配重位置变化因素；采用高速摄影对 Nelson SR100喷头的摇臂运动情况进行了试验研究，将得出的摇臂运动周期与计算结果进行对比，并通过改变配重安装位置来考察运动周期变化对喷头水力性能的影响。结果表明：通过高速摄影试验得到的摇臂运动周期与理论公式计算值吻合较好，相对误差基本在10%以内，验证了推导公式的正确性，针对理论公式的计算误差，根据试验结果对理论进行了修正，进一步提高了理论公式的计算精度，相对误差都在3%以内；增大喷头工作压力和前移配重安装位置均可使喷头的运动周期减小。配重位置距摇臂旋转轴较近时，喷头近处的喷灌强度明显增加，3～10 m内的水量分布较配重在最远处时增加了40%左右；配重位置距摇臂旋转轴远时，喷头近处的喷灌强度随之降低，射程末端的喷灌强度随之增加。该研究可为垂直摇臂式喷头摇臂设计方法的建立和在喷头运行过程中能合理调节摇臂配重提供参考。

As a kind of advanced water-saving irrigation technology, sprinkler irrigation system is adaptable to many crops, soils, and topographic conditions. At present, the most representative and most widely used sprinkler of the high pressure sprinklers are vertical impact drive sprinkler. In order to study the arm movement law of the sprinkler and the influence of counterweight on the hydraulic performance of the sprinkler, with the vertical impact sprinkler as the research object, this paper analyzed the arm movement characteristics of the vertical impact sprinkler by use of theoretic and experimental methods. The arm movement model of the vertical impact sprinkler was established, and according to this model, the free and non-free arm movement times were deduced and then the calculation formula of arm movement period was obtained. In this calculation formula, the factor of counterweight position change was taken into account. The experimental study on the arm movement of Nelson SR100 sprinkler was made with high-speed photography, then the experimental results of arm movement period were compared with the theoretical values, and the effect of arm movement period change on the hydraulic performance of the sprinkler was studied by changing the counterweight installation positions. The results showed that： the free and non-free arm movement times both decreased with the increase of working pressure under the same counterweight installation position. The free arm movement time was considerably larger than the non-free arm movement time, and over 90% of one arm movement period was free movement. In the free movement period, the curve of the arm angular displacement approximated to a smooth semi-period sine curve with the change of time. The arm movement period values obtained through the experiment of high-speed photography well coincided with the calculated values, with most of the relative errors within 10%, which verified the accuracy of the theoretical period formula. In view of the calculation errors of the theoretical period formula, the theoretical period formula was corrected according to the experimental results, thus further improving the calculation accuracy of the theoretical period formula with all the relative errors within 3%. The maximum rotation angle of the arm increased with the increase of the distance between counterweight and arm rotational axis, which increased the arm movement period and decreased the frequency of breaking water jet. Under the same working pressure, the non-free arm movement time increased while the free arm movement time decreased with the decrease of the distance between counterweight and arm rotational axis. Within one arm movement period, the arm angular velocity approximated to a smooth semi-period sine curve with the change of time. The arm angular velocity and movement period were both related to the counterweight installation positions. The farther the counterweight installation position was from the arm rotational axis, the bigger the arm angular velocity and period values became. Both the increase of the sprinkler working pressure and the distance between counterweight and arm rotational axis could decrease the movement period of the sprinkler. When the distance between counterweight and arm rotational axis was short, the sprinkling irrigation intensity near the sprinkler obviously increased and the water distribution increased by about 40% within 3-10 meters; when the distance between counterweight and arm rotational axis was long, the sprinkling irrigation intensity near the sprinkler decreased correspondingly and the sprinkling irrigation intensity at the end of sprinkling irrigation increased correspondingly. The results can provide valuble information for the establishment of the arm design method of the vertical impact sprinkler as well as the reasonable adjustment of the arm counterweight installation position during the operational process.