高水头短有压泄水孔掺气坎水体紊动喷溅猝发机制研究

When high dam short pressure drainage hole operates at high water level, prototype flood release observation finds of paroxysmal water surface severe rise and fall of aerator water, water splash beating cave top cover, etc., lead to noticeable vibration, endangering safety of the Project. Large-scale hydraulic model recheck test preliminarily reveals the special high-speed flow turbulence phenomenon. At present, domestic research into strong turbulent flow which breaks out of turbulence burst energy gathering is limited in depth, without profound understanding of its perniciousness and with water splash burst mechanism remaining unknown. This Project takes high-speed turbulent flow of short high-head pressured free flow hole with aerator as study object, intends to apply theoretical analysis, large-scale hydraulic model test and numerical calculation research method, to perform series researches into spatial and temporal distribution and development rules of aeration flow surface breaking, flow rate distribution, wall pressure and other turbulent features in terms of flow conditions formed by water splash burst and type of aeration facilities, reveal influencing mechanism triggering water splash and extent of injury from energy dissipation and diffusion angle, thus developing optimization measures to reduce adverse hydraulic characteristics. This study is of significance to enriching turbulent mechanics theory, present the physical quantity that represents the sudden burst of water body, put forward critical discriminant condition, and improving safety and stability of high dam flood release operation and widening hydraulic design thinking and methods of high head drainage hole.

设置掺气设施的短有压泄水孔在高水位泄洪运行时，原型观测发现掺气坎水体出现阵发性水面剧烈升降、猝发水翅喷溅击打洞顶盖板等现象，坝上建筑物出现明显振感，危及工程安全。大比尺水工模型复验试验初步揭示了这一特殊高速水流紊动现象。目前，国内外对紊流猝发能量聚集继而爆发的强紊水流特性及危害研究深度有限，紊流猝发喷溅机制尚不明晰。本项目以设置掺气坎的高水头短有压泄水孔高速紊动水流作为研究对象，采用理论分析、大比尺水工模型试验和数值计算研究方法，从水流条件及掺气设施等方面对水面破碎、壁面压力、流速、掺气浓度及空腔长度等紊动特性时空分布及发展规律进行系列研究，从能量耗损与扩散角度揭示水体喷溅及其危害影响的机理，提出表征水体喷溅猝发的物理量、临界判别条件以及减免不良水力特性的优化措施。该研究对揭示掺气坎水体紊动喷溅机理、丰富紊流力学理论、提高高坝泄洪运行安全以及拓展高水头泄水孔水力设计新思路具有重要意义。

短有压泄水孔是高坝工程中常见的一种泄水结构，原型观测发现，设有掺气坎的短有压泄水孔在高水位泄洪运行时，掺气水体出现阵发性水面剧烈升降、周期性喷溅击打洞顶盖板等不良水力现象。本项目采用理论分析、大比尺水工模型试验和数值计算研究方法，从水流条件及掺气设施等方面对壁面压力、掺气浓度、水舌冲击角、空腔形态等特征及发展规律进行了系列研究，揭示了水体喷溅及其危害影响的机理，提出了表征水体喷溅猝发的物理量、临界判别条件以及减免不良水力特性的优化措施。主要结论如下：.（1）研究归纳了不同水流条件下掺气坎水体紊动特性及特征指标。泄槽水面的上下摆动、掺气底空腔内回水前后移动幅值以及泄槽段水流脉动压力等均随水头的升高而加剧；H<77m时，回水波动幅值、通气量变幅、冲击角均较为稳定，变化较小，H>77m时，回水波动幅值、通气量变幅、冲击角均发生跃升，变化幅值较大，掺气水体紊动加剧，同时出现剧烈的水翅抬升现象。.（2）揭示了高水头短有压泄水孔掺气坎水体喷溅猝发机制。跌坎性水翅抬升与水舌冲击角存在较大的相关关系，其形成机理概括为“来流条件—水舌冲击角—掺气空腔形变—空腔脉动压力跃升—水翅抬升”，其相关关系层层递进。提出了喷溅触发临界判别条件：当跌坎水舌的冲击角不大于临界冲击角的40%时，水翅不会出现明显的抬升；当角度比大于1.4后，则水翅抬升幅度急剧增加，并随角度比成线性增加趋势。.（3）研究了掺气水体紊动喷溅敏感性因素。从掺气设施位置、坎高、挑角、泄槽底坡等因素出发，观测分析了不同因素对水体喷溅量、流速场、压力场、空腔回水、掺气量等指标的影响。结果显示：上游水头、通气方式、进流条件、掺气坎体型和下游泄槽底坡起到了关键性作用。.（4）提出了减免紊动喷溅危害技术。采用掺气坎负挑角、前移掺气坎位置或调整下游泄槽底坡，均能优化水舌冲击角，从而控制空腔回水摆动和空腔形变，缓解空腔脉动压力跃升，最终减免水翅抬升和泄槽水体产生爆发性喷溅。