准静态边界条件对输水系统水锤压力的影响研究

The transitions between different working conditions and the accidents that happen in a water conveyance system will both lead to hydraulic transients. The calculations, predictions and theoretical analysis of the hydraulic transients are all beneficial to the safe operation of the water conveyance system as well as the determination of the optimum schemes. Additionally, the precise description of the boundary conditions in the hydraulic transients is the prerequisite of the theoretical calculations. So far, quasi-static assumption is introduced in the calculations of the transient flow in the pressurized water conveyance system in varying degrees to describe the boundary conditions. However, the understanding of the impact of the quasi-static assumption upon the calculation results is not heretofore unified both here and abroad, and only qualitative conclusions have been obtained without adequate quantitative basis. This project chooses the dynamic hydraulic characteristics of various boundary conditions of the water conveyance system as the research objects, using the basic theories of the hydrodynamics, thermodynamics, etc. for reference, analyzing the impacts of various quasi-static boundary conditions upon the hydraulic transients in the water conveyance system on the basis of the synthesis of previous research results. Furthermore, in this way, the essential understanding of the hydraulic transients is deepened while the safe operation of the water conveyance system is ensured.

输水系统中各种运行工况之间的转换以及意外事故的发生，均将伴随复杂的水力过渡过程现象，对其进行计算预测、理论分析，不仅关系到输水系统的运行安全，而且是方案决策的重要依据，对水力过渡过程中边界条件的准确描述则是进行理论计算的基础。迄今为止，在对有压输水系统瞬变流计算的边界条件中均不同程度地引入了准静态假设，该假设对计算结果的影响国内外尚未形成统一认识，只有定性的结论，缺乏定量的依据。本项目以输水系统各类边界条件的动态水力特性为研究对象，借鉴水动力学、热力学等学科的基本理论，拟通过理论分析、数值模拟、模型试验与原型观测，在综合前人研究成果的基础上，分析输水系统中各类准静态边界条件对水力过渡过程的影响，在确保输水系统运行安全的同时加深对水力过渡过程现象的本质认识。

针对水力过渡过程中水流的准静态特性与动态水力特性的不符，本项目研究探寻了反映水流内部耗散性简单的一维数学表达式，使其能够与一维特征线法结合，提高计算的可靠度。通过理论分析、数值模拟和实验观测，探索了输水系统在发生水力瞬变时的动态水力特性，揭示了水力边界动态特性对输水系统水锤的影响，剖析了输水系统水流的准静态水力特性与动态水力特性的差别，研究了不同的准静态边界条件在水力过渡过程计算中所带来的误差。建立了描述不同实际边界条件下水力过渡过程数学模型，并编制了相应的数值仿真软件，总结了不同动态边界条件下的计算方法与原则、以及相应的水锤事故防护措施。明确了有压非均匀流、管道系统中水锤防护措施及管道边界条件、供水系统中部分水锤防护措施的阻抗孔口边界、管路中的阀门动态特性对输水系统水锤压力的影响。