强降雨期城市深层隧道竖井井喷机理与减免方法研究

Geysers are unexpected eruptions of air-water mixture through access manholes and other vertical shafts in drainage systems, which can lead to urban flooding, cause significant structural damages, and pose threats to pedestrians. Their occurrences are often related to flow transitions from gravity flow to surcharged flow, the subsequent air entrapment, its pressurization and release. As storm geysers have been reported around the world, the dynamics of air pockets in vertical risers and horizontal tunnels has been extensively studied. Although the role of entrapped air in causing large pressure transients was revealed, recent studies found that the dynamic pressure alone could not explain the observed height of geysers. Thus, the dynamics of the air/water interplay will likely need to be incorporated into our models. Despite those findings, our knowledge on the generation mechanism and scale effects is limited, and there are virtually no design guide for geyser prevention and mitigation measures...Accordingly, this study mainly focuses on: (1) geyser mechanisms and their conceptual models and/or formulas, (2) dominant factors and hydraulic characteristics of geysering flow including pressure oscillations over the process of air compression, expansion, migration and eruption in a trunk sewer and vertical shaft, (3) scale effects, and (4) potential solutions and their parametric optimization to prevent or reduce geysering. Theoretical analysis, physical and numerical (computational fluid dynamics) modelling methods will be jointly employed throughout the investigation. ..The objectives of the present study are: (1) to advance our understanding of the nature of geysers, predict surges incorporating air phase, and develop analytic and numerical models for geysering flows, and (2) to evaluate measures and propose practical design guidelines for preventing and/or alleviating geysers. This study will be helpful to supplement the existing theory of air-water pipe flows, guide the retrofitting and modernization of our existing sewers, and design deep tunnel sewerage systems to deal with the challenges due to the climate change and rapid urbanization.

城市深层隧道竖井井喷是截留空气经由竖井释放引发的水气混合物射流现象。井喷通常发生在强降水过程中，可导致城市局部地区内涝，造成管道结构性破坏，并给行人带来安全风险。由于井喷现场观测资料少、流动复杂、随机性强，目前研究对其形成机制认识不足，缺乏水气耦合作用的量化分析，尚未提出解决井喷问题的有效方法。.本项目拟采用理论分析、物理模型实验和数值模拟方法综合研究气囊释放过程、井喷模式及其形成机理，阐明井喷与瞬变压力的响应关系，揭示压力演变过程及水气运动规律；分析井喷主控影响因素及其阈值，探求空气相的定量作用；通过开展系列物模实验及数值模拟，建立水气耦合作用的比尺效应修正公式；基于上述研究，结合源头、过程、末端控制方法，提出预防和缓解井喷的有效措施。.本研究预期将阐明不同模式井喷的形成机理并提出减免井喷的有效方法，有助于补充发展管道水气动力学理论，为城市深层隧道排水系统设计运行提供理论依据和技术支撑。

强降雨易造成城市雨洪排水系统负荷过载、空气截留，从而引发井喷现象。由于井喷现场观测资料少、流动复杂、随机性强，现有研究对其形成机制认识不足，缺乏水气耦合作用的量化分析，尚未提出解决井喷问题的有效方法。本项目在理论分析层面，对竖井井喷现象的核心阶段——气囊压缩过程进行了深入探究，基于非线性系统平衡点的雅可比线性化方法，提出了压力波动过程幅值、周期的显式表达式，揭示了压力振荡特性与系统参数之间的关系。在模型方法层面，建立了非满流管道快速填充边界条件下刚性水体-理想气体的水气两相瞬变流一维数学模型，通过对非满流管道快速填充的控制方程进行无量纲化分析，主要探究了尾水深度对系统压力波动的影响；分别基于OpenFOAM、ANSYS CFX建立了三维可压缩水气瞬态流动的CFD模型，在量化分析瞬变过程中水气耦合作用、压力波动、尺度效应的基础上，对比优化了几种有效缓解井喷的方法。模拟计算结果表明，井喷形成过程中水流瞬时流场与水锤类似，水气耦合对压力波动具有一定的阻尼作用。研究发现组合使用导流孔板与通气孔缓解井喷效果最为显著，压力极值可降低65%。本项目的研究成果有助于深入理解井喷形成机制，为设计相应的缓解措施提供理论基础与数据支撑。