Experimental Study on Discharge and Energy Dissipation of Baffle-Drop Shaft in Deep Tunnel Drainage System
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摘要: 针对深隧排水系统竖井泄流过程中高速气-水两相流动特性进行了水力模型试验研究，观测竖井内水流下泄过程中的型态，分析最大泄流量与折板间距的关系，计算不同工况下的竖井消能率，并揭示折板型竖井在泄流过程中的消能机理. 试验结果表明：竖井在泄流过程中存在3种水流型态：撞壁受限流、临界流和自由跌水流；泄流过程中水跃是水流在折板上消能的主要原因，水流流至井底与反向流体互相撞击破碎使竖井达到最终消能的目的；当竖井直径D = 0.4 m、折板间距d介于16.02～24.56 cm时，竖井最大泄流量介于（8.7～14.7） × 10−3 m3/s，且d与最大泄流量Qm存在线性关系；根据能量守恒定律推导出消能率公式，得到d = 19.4 cm、倾角θ = 10° 时的竖井消能率为最优；竖井盖板开孔直径 Ф 对竖井顶部压强的影响较大，当 Ф ≥ 4 cm时，竖井顶部相对压强基本为0，并且具有一定倾角的折板有利于加速竖井的泄流过程；上、中、下折板冲击力（Fu、Fm、Fd）呈现Fu > Fm > Fd 的分布规律，上、中、下折板最大面荷载分别为42.8、30.7、22.8 kN/m2. 深隧排水折板型竖井最佳泄流量和最优消能率的试验研究成果对深隧竖井工程的设计与运行提供了一定参考价值.Abstract: In order to study the transition characteristics with the high-speed air-water flow in the drop shaft of a deep tunnel drainage system, a hydraulic model test was conducted to observe the flow patterns in the process of drop shaft discharge, analyze the relationship between the maximum discharge and the baffle spacing, and calculate the energy dissipation rates of the drop shaft under different conditions. On this basis, the energy dissipation mechanism in the process of drop shaft discharge was revealed. Results show that there are three kinds of flow regimes in the discharge process of drop shaft, i.e., wall-impact confined flow, critical flow, and Free-drop flow. Hydraulic jump is the primary cause of energy dissipation of water on the baffle, and the collision of the water flow with the bottom-drop shaft fluid in the reverse direction and the resulted breakage achieve the ultimate purpose of energy dissipation. The maximum discharge of drop shaft is between 8.7 × 10−3 and 14.7 × 10−3 m3/s when the shaft diameter D = 0.4 m and the baffle spacing d ranges from 16.02 to 24.56 cm, and there is a linear relationship between the baffle spacing and the maximum discharge (Qm). The formula of energy dissipation rate is deduced according to the law of conservation of energy, from which the optimal energy dissipation rate of drop shaft is achieved at d = 19.4 cm and inclination angle θ = 10°. The aperture diameter (Ф) of the cover-plate has a great influence on the internal pressure of the drop shaft. When Ф ≥ 4 cm, the internal pressure is nearly 0; the baffle with a certain inclination angle is conducive to accelerating the discharge process of the drop shaft. The impact forces on the upper, middle and lower baffles (denoted by Fu, Fm and Fd, respectively) present a relation of Fu > Fm > Fd; the maximum surface loads of the upper, middle and lower baffles are 42.8, 30.7 and 22.8 kN/m2, respectively. The experimental results about the maximum discharge and optimal energy dissipation rate of baffle-drop shaft could provide a reference for the design and operation of the baffle-drop shaft of deep tunnel drainage systems.
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图 10 不同工况下折板竖井消能率
Figure 10. The energy dissipation rate of drop shaft under different conditions
图 12 Ф=0 cm工况竖井顶部压强最值
Figure 12. Pressure of drop shaft top at the condition of Ф=0 cm
图 13 不同工况下折板冲击力时程曲线
Figure 13. Impact time history of baffle under different conditions
表 1 试验采用的相似比尺
Table 1. Scale relations and ratios of model system
名称 比尺关系 相似常数 长度 λl 25.00 时间 λt = λl0.5 5.00 流速 λv = λl0.5 5.00 流量 λQ = λl2.5 3 125.00 力 λF = λρλl3 15 625.00 压强 λP = λρλl 25.00 糙率 λn = λl1/6 1.71 
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表 2 试验因素水平表
Table 2. Factors of the orthogonal test
折板间距 d/cm 折板倾角 θ/（°） Ф/cm 16.02 0 0 2 19.40 10 4 6 24.56 20 8 10
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