高扬程虹吸排水合理管径数值模拟

发布时间：2018-04-18 06:54

本文选题：虹吸排水 + 完整弹状流　；参考：《浙江大学》2014年硕士论文

【摘要】：滑坡是一种常见的地质灾害,降雨容易引起坡体地下水位的上升,从而诱发滑坡。地下水主要通过软化土体、增加土体自重、渗透力作用影响边坡稳定性,因此及时排出坡体内的地下水可以有效防止滑坡的发生。当前排水措施施工复杂、长期排水效果差、费用高。而虹吸排水技术具有免动力排出深部地下水的优势,且施工简单,造价低,值得在边坡治理工程中推广应用。论文提出边坡虹吸排水这一方法,该排水方法具有可实现深部排水、施工简单、造价低等优点。但因边坡排水涉及高扬程,在虹吸管内的低压环境中流动时液体会发生强烈的空化现象,从而产生气液两相流。在间歇性虹吸排水过程中,随着虹吸管两侧液面高差的下降,流速慢慢降低,虹吸管气液两相流通区域是一个从泡状流向弹状流转变的过程,如果流速过慢不能及时将析离的气泡带走,气泡会积聚在虹吸管顶点附近,形成附壁弹状流,空化现象将加剧,气泡堵住整个管道时,虹吸管右侧真空度不断降低,破坏虹吸现象的连续性,最终导致虹吸过程中断。通过对管内两相流型分析,发现只有形成完整的弹状流,才能将气泡带走,从而保证虹吸的长期有效。采用流体数值计算分析软件FLUENT的VOF模型,分别对管径为4mm、5mm、6mm、8mm的虹吸管内的气液两相流型进行模拟,结果表明：管径小于5mm的条件下,表面张力起主要作用,能形成完整弹状流；管径大于6mm的条件下,会形成附壁弹状流。该结论与物理模型试验结果一致,表明数值模拟分析结果可靠。采用4mm管径虹吸管,通过改变壁面粗糙度和接触角进行数值模拟,结果均表明能形成完整弹状流,说明壁面粗糙度对流型的影响不大,接触角的改变会影响完整弹状流的形状,但不会造成气泡的积聚。
[Abstract]:Landslide is a common geological hazard.Groundwater affects slope stability mainly by softening soil, increasing soil weight and permeability, so timely discharge of groundwater from slope can effectively prevent the occurrence of landslide.Current drainage measures are complex in construction, poor in long-term drainage effect and high in cost.The siphon drainage technology has the advantage of eliminating the power from the deep groundwater, and the construction is simple and the cost is low, so it is worth popularizing and applying in the slope treatment engineering.This paper presents a siphon drainage method for slope, which has the advantages of deep drainage, simple construction and low cost.However, because the slope drainage involves high lift, the liquid will occur strong cavitation when flowing in the low pressure environment in the siphon, thus the gas-liquid two-phase flow will occur.In the process of intermittent siphon drainage, with the decrease of the height difference between the two sides of the siphon, the velocity of flow slowly decreases, and the gas-liquid two-phase flow region of the siphon is a process from bubbly to slug.If the flow rate is too slow to take away the separated bubble in time, the bubble will accumulate near the top of the siphon tube, forming a wall attached slug flow, and the cavitation phenomenon will be intensified. When the bubble blocks the whole pipe, the vacuum degree on the right side of the siphon pipe is continuously decreasing.The continuity of siphon phenomenon is destroyed, and finally the siphon process is interrupted.Through the analysis of the two-phase flow pattern in the tube, it is found that only when a complete slug flow is formed, can the bubbles be taken away, thus ensuring the long-term effectiveness of siphon.The gas-liquid two-phase flow patterns in a siphon with a diameter of 4 mm ~ 5 mm ~ 6 mm ~ 8 mm are simulated by the VOF model of the fluid numerical analysis software FLUENT. The results show that when the diameter of the pipe is smaller than 5mm, the surface tension plays a major role and the complete slug flow can be formed.When the diameter of the tube is larger than 6mm, a wall-attached slug flow will be formed.The conclusion is consistent with the results of physical model test, which indicates that the numerical simulation results are reliable.By changing the wall roughness and contact angle, the numerical simulation of 4mm pipe diameter siphon is carried out. The results show that the complete slug flow can be formed, which indicates that the wall roughness has little effect on the convection pattern, and the change of contact angle will affect the shape of the intact slug flow.But it does not cause bubbles to accumulate.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU753.8;TV134

【参考文献】