陡坡隧洞明满交替流水力特性研究

The steep-grade tunnel has the properties of high velocity flow and being easy to cause mixed free-surface-pressure flow, which can cause the periodic changes of hydrodynamic pressure, flow velocity etc., resulting in impact damage, cavitation erosion and vibrative damage easily, threatening the tunnel structure stability and operation safety. The formation mechanism and hydraulic characteristics of this kind of mixed free-surface-pressure flow appearing in the steep-grade tunnel is different from that happening in power station's tail tunnel and underground city water pipe grid. This project chooses the steep-grade tunnel's mixed free-surface-pressure flow as object of study. By the study method combination of model test, numerical simulation and theory research, it plans to solve the following key scientific problems: (1) revealing the happening mechanism of the steep-grade tunnel's mixed free-surface-pressure flow, revealing the distributing rules of such air-liquid boundaries as entering air, air emission, mixed air-water flow, air cell's form change and its movement etc. (2) establishing a transient-flow mathematics model adopting characteristic implicit format method with the consideration of the air-liquid boundaries mentioned above, studying the quantitative response relationship of the mixed free-surface-pressure flow discharge interval and the main factors of influence. (3) putting forward the controlling measures to reduce mixed free-surface-pressure flow's harm to the steep-grade tunnel. The research project has important scientific meaning to reveal the mechanism of the steep-grade tunnel's mixed free-surface-pressure flow. The related quantitative descriptive procedure and basic theory about the hydraulic property of the steep-grade tunnel's mixed free-surface-pressure flow can provide the important scientific and technology support for the steep-grade tunnel design optimizing and the guarantee of tunnel operation safety.

陡坡隧洞具有高速水流及易发生明满交替流特性，由此引起的洞内水流压力、流速等周期性变化，易对隧洞产生冲击、空蚀及振动破坏而危及隧洞运行安全，其形成机理和水力特性有别于以往研究较多的电站尾水洞及城市地下水管网。本项目以陡坡隧洞明满交替流为研究对象，通过模型试验、数值模拟、理论研究相结合方法，拟解决以下关键科学问题：（1）阐明陡坡隧洞明满交替流的形成机理及发展过程，探明隧洞进气、排气、水气掺混以及气囊涨缩运移等气液边界的分布规律；（2）构建考虑隧洞进排气、水气掺混以及气囊涨缩运移的陡坡隧洞特征隐式格式法瞬变流计算模型，研究陡坡隧洞中明满交替流的流量区间与主要影响因子的定量响应关系；（3）分析提出减轻陡坡隧洞明满交替流危害的控制措施。本研究对阐明陡坡隧洞明满交替流机理有重要科学意义，对陡坡隧洞明满交替流水力特性的定量描述方法及基础理论，可为科学指导陡坡隧洞设计，保障隧洞运行安全提供重要的科技支撑。

陡坡隧洞易发生明满交替流，形成迅速膨胀收缩气囊，使洞内水流压力、流速等发生周期性变化，易产生空化空蚀、振动、冲击破坏而危及隧洞运行安全。本项目采用理论分析、物理模型及数值模拟相结合手段，对陡坡隧洞明满交替流的形成机理、明满交替流与各因素的相互作用关系以及改善措施进行了研究。研究表明：.（1）陡坡隧洞明满交替流的主要影响因素有洞前相对淹没深度 、隧洞体型（隧洞底坡、进口顶部体型、洞高、洞长、是否有转弯段、闸门井等）、进口引渠布置以及由上述因素形成的吸气漩涡、闸门井吸气影响等。.（2）导流洞内是否形成C2型曲线并封闭洞顶是产生洞内明满交替流的先决条件；被封闭的气囊会受其他因素影响发生迅速膨胀压缩变形，是产生洞内明满交替流的内部条件；受进口漩涡吸气、门井吸气、洞顶负压等影响，造成导流洞出口顶部无足够的进气或排气面积，致使导流洞进、排气不畅，是产生洞内明满交替流的外部条件。上述条件同时作用产生明满流现象。因此，这些条件便构成了该类明满流现象发生、发展及形成的机理。.（3）当隧洞为缓坡隧洞时，尽管隧洞进口水位变幅较大，发生了贯通式吸气漩涡，且隧洞较长，洞内还是未发生明满交替流。由此可见，进口漩涡、隧洞长度并非洞内明满交替流产生的根本原因。.（4）物理模型及4种底坡的陡坡隧洞数值模拟计算成果成果表明：隧洞底坡较陡是产生明满交替流的最主要因素。进口漩涡吸气、闸门井吸气影响加剧、扩大了明满交替流流量区间；上游水位运行区间跨越了吸气漩涡区易于形成漩涡、进口喇叭口段洞顶负压造成闸门井在高水位时形成吸气均加剧了明满流交替的形成，扩大了其流量区间。洞顶负压值在发生明满交替流时，随底坡增大呈现负压增大且不稳定状态，使洞顶长期处于交变负荷作用下而危及隧洞运行安全。.（5）采取隔流浮堤、进口引渠对称布置+隔水墙等进口消涡措施；锐缘进口、短轴较长的1/4椭圆的曲线进口等进口体型优化措施；出口压坡以及洞高、洞长优化等复合式措施，可减免陡坡隧洞洞内明满交替流。