地下滴灌多孔出流特性及均匀度数值模型研究

The emitter flow of subsurface drip irrigation (SDI) changes because it is affected by soil texture. Meanwhile, the drip pipe is compressed by soil gravity. The head loss would increase. Therefore, the flow characteristics are very different from surface drip system. However, the hydraulic design of SDI system mainly depends on the standards of surface system, which causes several problems. For example, the emitter flow drops and deviates dramatically from designed value and crop grows unevenly in the field. This project plans to propose a new water application uniformity model for SID system based on its specific multi-orifice out-flow features. The experiments and CFD numerical simulation will be conducted to explore the soil’s effect on pipe deformation and the internal resistance formation mechanism. Then, the calculation method for local head loss will be proposed. The effects of soil porosity and emitter parameter on flow rate will be demonstrated. The equation for computing emitter flow rate will be derived based on “back pressure” theory. Using the formulas and the finite element method, a uniformity calculation model for looped pipe network will be established considering the combined effects of hydraulic variation, manufacturing variation, topographic deflection and soil spatial variability. Based on the uniformity model, a new hydraulic design procedure will be proposed by using nonlinear optimization theory and genetic algorithm. A custom computer software script will be programmed to implement the method, and the features of SDI technical parameters will be revealed. This project will help to understand the hydrodynamics characteristics of SDI multi-orifice out-flow system from exploring the flow variation mechanism. It will conquer the disadvantage of current design theory, which will provide the theoretical support for improving our nation’s microirrigation engineering design specifications.

地下滴灌滴头流量受到土壤质地的影响发生变化，同时管道发生压缩形变引起水流阻力增大，具有特殊的出流规律。目前其水力设计方法主要依据地上滴灌的技术规范，造成流量不足、作物长势不均等诸多问题。为此，本项目拟通过土箱试验和CFD数值模拟，揭示地埋滴灌带受压形变规律，内部阻力形成机理和计算方法，探明土壤孔隙率和滴头水力参数对流量的影响，基于正压理论提出流量计算公式；在此基础上，应用有限元数值分析原理，依据地下滴灌出流特性，建立考虑水力偏差、地形偏差、制造偏差、土壤空间变异的环状管网均匀度数值模型，阐明均匀度变化规律；应用模型，结合非线性优化理论和遗传算法，建立一种新的水力设计方法，编写计算机软件对压力、流量等指标进行优化，揭示地下滴灌技术参数特征。本项目从探索多孔出流规律出发重新认识地下滴灌水动力学特性，提出的均匀度模型有助于解决现有设计理论带来的问题，为完善我国微灌工程技术规范提供理论依据。

地下滴灌作为一种高效节水灌溉技术，具有环状灌水管网的特殊形式，同时管道和灌水器受到土壤荷载和导水特性的影响，与地上滴灌系统表现出完全不同的水力特征（管网压力分布、滴头流量、灌水均匀度）。目前地下滴灌的水力设计主要依据地上系统的《微灌工程技术规范》，造成部分工程系统失效。针对此问题，在国家自然科学基金的资助下，通过研究，提出了薄壁内镶贴片式滴灌带局部水头损失计算方法，探明了土壤荷载对管道形变和内流阻力的影响，基于此，对比分析了地上和地下毛管内压降规律。揭示了地下滴灌滴头出水口处土壤正压—饱和导水率—流量的动态互馈机制，分析了淹没出流土壤正压形成和变化规律及对滴头流量的影响，提出了滴头流量计算方法。 基于有限元分析原理，建立了适用于不同管网形式的滴灌水力计算模型，应用前两点研究成果，在考虑土壤特性空间变异的条件下，阐明了地下滴灌均匀度变化规律。应用模型，计算得到了不同工况下的水力设计结果，对地下滴灌工程设计提出了针对性建议。研究成果能够为丰富地下滴灌设计理论和完善我国微灌工程技术规范提供科学依据。