High-lift siphon flow velocity in a 4-mm siphon hose

Abstract

High-lift siphon drainage by 4-mm internal diameter siphon hoses is a real-time, free-power, and long-term approach for slope drainage. The conventional hydraulics formula for pressurized pipe flow is generally used to calculate the single-phase velocity of siphon flow. However, an intensive cavitation phenomenon occurs in the high-lift siphon hose and then a two-phase flow is formed. Research on the velocity of high-lift siphon flow is a prerequisite for the application of siphon drainage with a 4-mm siphon hose. Few investigations of this subject have been carried out. Hence, experiments on the high-lift (8 m≤H ₀≤10.3 m) siphon drainage in a 4-mm siphon hose were performed. The characteristics of siphon flow under different conditions were observed and test data were obtained. Comparisons between test results and calculated results showed that significant errors were given by the hydraulics formula. It is demonstrated that the effect of gas in a siphon hose should be included in the calculation of flow velocity. The findings can be used to determine the number of siphon hoses and layout of siphon drainage holes, and provide valuable information for geotechnical companies.

摘要

目 的

探索高扬程条件下4 mm 虹吸管内气体集聚现象对虹吸流速的影响,并对传统虹吸流速水力学计算公式进行修正。

创新点

1. 通过对比物理模型实验值和计算值,得出了高扬程虹吸流速的控制因素及传统虹吸流速计算公式在高扬程条件下的不适用性;2. 通过分析实验数据,对有压管流水力学公式进行修正,使之适应高扬程条件下的虹吸流速计算。

方法

通过物理模型试验,揭示高扬程虹吸流速的特征(图3);将高扬程虹吸流速实验值和传统虹吸流速水力学公式计算值进行对比(表3 和4);通过分析实验数据,结合有压管流水力学公式,得出高扬程虹吸流速经验公式(公式(5)和(8))。

结论

1. 在高程差H ₁ 一定时,虹吸流速与扬程呈负相关;在扬程H ₀ 一定时,虹吸流速随高程差H ₁的增大而流速加快,直至达到最大流速,并保持稳定状态;虹吸流速与管长呈负相关。2. 高扬程虹吸排水由于管内气压降低析出大量气泡,形成气液二相流,影响虹吸流速的计算;目前采用的有压管流水力学计算公式不适用高扬程4 mm 虹吸管的虹吸水流。3. 当H ₁<2ΔH, 虹吸流速的控制因素为高程差H ₁;当H ₁≥2ΔH, 虹吸流速的控制因素为当地虹吸极限扬程H _max 和H ₀ 的差值ΔH;4. 对于高扬程4 mm 虹吸管虹吸流速的确定,一是可以直接实验测定,查找相关数据,二是可以采用经验公式来确定相关的虹吸流速。