用凯勒均匀度进行微灌系统设计的质疑

用凯勒均匀度指标进行微灌系统设计的方法,美国还在使用,为了探讨该设计方法是否正确,该文从凯勒均匀度的定义与多孔出流管水力学原理出发,对凯勒均匀度的两种定义进行比较分析后,认为两种定义有实质性差别,不能混淆.凯勒均匀度的田间实测数据计算公式(定义1)只能作为微灌系统的后评价指标,用凯勒均匀度指标进行微灌系统设计的方法,是以制造偏差系数为基础的(定义2),而后者只是工作压力最小点的灌水器出流特征,作为设计指标,缺乏合理性;该方法中用推荐均匀度(EUT)来替代计算均匀度(EU),导致最小压力灌水器的流量期望值计算公式缺乏科学根据;而允许水头差计算公式与多口管水力学规律不符.出现上述错误的原因,在于当时多口管水力学研究还不成熟,而微灌生产实际又迫切需要设计方法.时至今日,应该重新审视这一设计方法.

Query about micro-irrigation system design using Keller Uniformity

Keller Uniformity is recommended by USDA-SCS to design micro-irrigation system. In order to discuss whether the method is correct or not, Keller Uniformity and the design method of micro-irrigation system were discussed in detail according to the definitions of Keller Uniformity and hydraulics principle of multiple-outlet pipeline. The comparative analysis of the two definitions of Keller Uniformity indicates that there is substantive and completely difference between the two definitions, which cannot be confused. The formula of Keller Uniformity using field measured data (definition 1) is only used as an after-evaluation indicator of micro-irrigation system. The micro-irrigation system design using Keller Uniformity was based on manufacture deviation index (definition 2), and the later definition is only the outflow characteristic of the minimal working pressure point. As a design index, it is not reasonable. In this method calculated evenness(EU) was replaced by recommended Uniformity (EUT), which leads to the flow expectation calculation formula of emitter under the smallest-pressure lack of scientific basis, while the calculation formula of allowable pressure head differences does not match with the hydraulics law of multiple-outlet pipeline. The cause for the mistakes was that the hydraulics knowledge of multiple-outlet pipeline was incomplete at that time, while the practice of micro-irrigation urgently needed a design method. So up today this design method should be re-examined.