城市雨洪排水系统中“间歇泉”现象的瞬态特性及发生机理研究

Transient flow with large entrapped air pockets would occur in the urban stormwater drainage systems during extremely strong rain events. Geysers, which involve the explosive release of water or air-water mixtures through vertical shafts, have been attributed to violent air-water interactions in pipeline. The abnormal high water hammer during geysering most likely cause pipe structural damages. Rapid urbanization, extreme rainfall over return period and drainage-storage combination of “Sponge City”, induce that the problems described above occur frequently in recent years. So far, the transient behaviors and formation mechanisms of geysering are still limited and fragmented. Based on our previous investigations on the transient flow with entrapped air pockets, theoretical analysis, three-dimensional numerical simulation, experimental observation with high-speed photograph processing technique and the filed investigation are combined and used in this research program. According to the geometric characteristics of actual urban stormwater drainage systems and the inflow behaviors during extreme strong rain events, the mechanisms for air pocket entrapment, the three-dimensional dynamic characteristics associated with air pocket displacement, pressurization, expansion, and deformation, and the change rule during the transient process, are investigated carefully. In addition, the transient characteristics of geysering, and air-water two phase flow behaviors in vertical shafts during the explosive release of water or air-water mixtures are explored. The dynamic mechanisms of interactions between the geyser and the flow characteristic near the geyser are also conducted. Finally, the numerical modeling methods for the special transient flow involved geysers, and protection methods avoiding geysers, are proposed. All above work is significant and practical for warning and forecast of urban storm flood and comprehensive stormwater management.

在超设计标准降雨情况下，城市雨洪排水系统中将出现含大体积滞留气团瞬变流，其剧烈的气水相互作用会诱发竖井井口处爆发性释放的“间歇泉”现象，其对应的异常水锤足以引起系统结构破坏。近年来，快速城市化、超重现期降雨及“海绵城市”排蓄结合等致使上述现象频繁发生。目前，国内外对于这种特殊瞬变流的瞬态特性和发生机理尚缺乏准确认识。依托本课题组在含滞留气团瞬变流方面的研究基础，本项目拟采用理论分析、三维数值模拟和基于高速摄影-图像处理的实验测试及实地观察分析相结合方法，根据城市雨洪系统结构和极端降雨情况的来流特性，研究大体积气团的滞留机理和气团运动、压缩、膨胀、变形的三维动态特性及变化规律；研究“间歇泉”爆发的瞬态特性、竖井中气水两相流场特征及其流动特性；探索“间歇泉”与相邻区域流动之间互激扰动的动力机制；提出该特殊瞬变流的模拟分析理论、预测及防护方法。这对城市暴雨洪水预警预报和综合雨洪管理具有重要意义。

在超设计标准降雨情况下，城市雨洪排水系统中常会出现水气两相耦合瞬变流、“间歇泉”现象，由此产生异常压力波动极可能造成管道破坏事故。目前，关于这种特殊瞬变流现象的瞬态特性和发生机理尚缺乏准确认识。本项目研制和搭建了高分辨率量测系统实验台，完成了水流冲击滞留气团瞬变流、“间歇泉”现象的实验研究；系统研究了大体积气团的滞留机理和气团运动、压缩、膨胀、变形、排放的三维动态特性及变化规律；研究“间歇泉”爆发的瞬态特性、竖井中气水两相流场特征及其流动特性；探索“间歇泉”与相邻区域流动之间互激扰动的动力机制；提出了水气耦合瞬变流的仿真计算模型和数值模拟方法。这对城市暴雨洪水预警预报和综合雨洪管理具有重要意义。.（1）搭建了恒压供水系统水气耦合瞬变流的可视化实验平台。.（2）揭示了气团滞留-压缩-膨胀-变形-排放的动态特性及水气耦合作用规律。.（3）弄清了水流冲击滞留气团过程中水气耦合的热力学特性。.（4）揭示了“间歇泉”爆发过程的瞬态特性及发生机理。.（5）揭示了两个竖井的“间歇泉”的瞬态特性及相邻管内区域流动特性的相互影响机理。.（6）建立了水气耦合瞬变流的三维精细化CFD数学模型.（7）建立了水流冲击滞留气团的动态摩阻及水-气-管壁传热模型，揭示了水气两相能量耗散机理及变化规律。.（8）推导建立了基于有限体积法Godunov格式水-气瞬变流数学模型。.依托本项目，培养博士、硕士生8名（毕业4名，在读4名）。发表论文18篇，另有8篇中文期刊论文录用，均标注本项目资助。9篇SCI，均发表在Journal of Hydraulic Engineering–ASCE(5篇)、Journal of Hydraulic Research-IAHR(3篇)、Journal of Hydro-environment Research(1篇)水力学领域国际著名期刊。发明专利授权6项，发明专利受理8项。软件著作权1项。