分流式灌水器结构优化设计与试验

水力性能和抗堵性能是评价灌水器性能的2个重要指标,但两者在对灌水器流道的结构要求上存在本质的矛盾,目前缺少有效的灌水器结构优化方法。为了定量优化出2方面性能都比较优越的流道结构,该文将渐缩、渐扩、分流等增大局部压力损失的方法应用到灌水器流道设计中,设计了一种分流式灌水器,提出基于灰靶理论的灌水器流道多目标优化方法;将正交试验方法和灰靶理论相结合,进行面向水力性能和抗堵性能的灌水器流道多目标优化。研究结果表明,当给定水力性能和抗堵性能权重均为0.5时,最优结构参数水平组合为A3B4C2D4,此结构的流道流态指数为0.5150,粒子通过率为88.504%,综合考虑了水力性能和抗堵性能2个目标。通过试验验证,该方法是灌水器流道结构设计与定量优化的有效方法。

Optimal design and experiment for divided-flow emitter in drip irrigation

Abstract: Hydraulic and anti-clogging performances are two important evaluation indicators for drip irrigation emitters. But the two indicators are in conflict when the two design requirements for emitter channel should be satisfied simultaneously. On one hand the channel should be long, narrow and meandering to have good hydraulic performance, but on the other hand it should be short, wide and smooth to obtain good anti-clogging performance. Multi-objective optimization for the emitter channel was reported by Zhang Jun in 2009. The main difficulty lies in the lack of quantitative indicator for the anti-clogging performance of emitters. This paper applied several ways including gradual reduction, gradual divergence and dividing flow to increase local pressure loss in emitter channel design and proposed a multi-objective optimization method for the channel of drip irrigation emitter based on grey target theory. This method combined orthogonal experimental design with grey target theory which is powerful to solve the problems with the uncertainty due to less data, little sample and incomplete information to optimize the emitter channel, with the goal of obtaining reasonable hydraulic and anti-clogging performances. As Computational Fluid Dynamics (CFD) analysis has been widely used in the research on drip irrigation emitters and proved to be effective by many experts, it was adopted to get the orthogonal experimental results in this paper. First, two quantitative indicators for the emitter's hydraulic and anti-clogging performances were defined respectively. The quantitative indicator for the hydraulic performance was flow state exponent. And the quantitative indicator for the anti-clogging performance was particle passing rate which was the ratio between the number of outgoing particles and total particles into the channel. Second, CFD analyses were carried out under different boundary conditions. Third, the results of the orthogonal design were obtained and analyzed with intuitive comparative analysis, variance analysis and linear regression analysis. And then the relationships between the two quantitative indicators and channel parameters were obtained. Fourth, the relationships were used to get more information in this problem, and the data group was extended from 16 to 256. Fifth, grey target theory was employed to analyze the data obtained. The results showed that the preferential sequence could be obtained according to the target heart rate which was an important concept in grey target theory. When the weights of hydraulic and anti-clogging performances were both 0.5, the best combination of factor levels for the emitter channel was A3B4C2D4, and the largest target heart rate was 0.795. The optimal channel had a flow state exponent of 0.5150 and a particle passing rate of 88.504%. When the channel was optimized aiming at single objective, the smallest flow state exponent was 0.5136 and the highest particle passing rate was 95.642%. Of course, seen from the comparison of the results between the multi-objective optimization and single-objective optimization, it is difficult to simultaneously get the best result for each target in multi-objective optimization. It is worth noting that when different performance combinations are needed, different weights should be given to the two quantitative indicators. This method provides a quantitative approach to guide the design of emitter channels.