变坡长隧洞明满流水力特性研究

Hydraulic Characteristics of the Free-Surface-Pressurized Flow in the Long Tunnel with Variable Slope

明满流交替是长隧洞常遇到的不利水流流态,尤其是洞内截留气囊输移现象会对隧洞结构安全构成威胁。通过试验研究,阐述了变坡长导流隧洞洞内流态的演变过程,指出随着上游水位上升,洞内水流流态呈现由水跃转变为明满流交替、直至有压流的演变过程,分析了典型流态下隧洞的泄流能力,得到了明满流交替的流量系数介于无压流和有压流流量系数之间的结论。同时探讨了明满流交替过程的压力波动,发现明满流交替的压力波动持续时间较长、振幅较大,但压力峰值持续的时间很短,并且截留气囊可有效减缓隧洞底部压力波动。

Free- surface-pressurized flow is a typical unfavorable flow which is often encountered in long tunnels. The phenomenon of en-trapped air transport will give rise to great threats to the tunnels5 safety. Based on the experimental research,the evolution process of flow in a long tunnel with variable slope was expounded in this paper. It show-ed that the transition of the flow experiences the hydraulic jump,the free- surface-pressurized flow and the pressure flow with the rise of the upstream water level. The analysis of the discharge capacity of each flow showed that the flow coefficient of the free- surface-pressure flow- was between those of the pressure flow and the free flow. The character-istics of pressures during the free- surface-pressurized flow were also studied in this paper. The alternate pressure fluctuation of the free- sur-face-pressurized flow kept a long time with a large amplitude, but the time of peak pressure was very short. The existence of the entrapped air would lower the pressure fluctuations which occurred at the bottom of the tunnel.