Abstract:

Water-rich slopes are prone to landslides and even debris flows. Slope drainage is widely used in slope engineering as an important means of geological disasters prevention. It is known that siphon drainage has the merits of real-time and power-free however, high water level in slope drainage will generate low-pressure environment, and flow liquid shows intensive cavitations phenomenon under such circumstance, which finally leads to gas-liquid two phase flow patterns. If the bubble is not removed promptly, it will accumulate at the top of the pipe in the intermittent siphon drainage process of low flow rate, and ultimately undermine the entire siphon process. In this research, VOF model in a fluid numerical software “FLUENT” is used to analyze two-phase flow patterns, it is found that only complete slug flow could carry the bubbles off and ensure long-term stable operation of the siphon drainage. We also simulate the air and flow patterns in siphon pipes of 4，5，6 and 8 mm in diameters. Simulation results show that the surface tension plays a major role for the pipes with diameters of less than 5 mm, which can form complete slug flow. On the other hand, mural slug flow shows for those diameters are larger than 6 mm. This numerical simulation results are also been proved by physical model tests.

Key words: siphon drainage, complete slug flow, mural slug flow, pipe diameter selection