非饱和花岗岩残积土水-气两相驱替过程数值模拟

蔡沛辰; 阙云; 李显

doi:10.16030/j.cnki.issn.1000-3665.202010017

非饱和花岗岩残积土水-气两相驱替过程数值模拟

福州大学土木工程学院，福建福州　350108

基金项目: 国家自然科学基金项目(41772297)；福建省自然科学基金项目(2018J01771)

详细信息

作者简介: 蔡沛辰(1998-)，男，硕士研究生，主要从事细观尺度渗流研究工作。E-mail: peichen_fut@qq.com

通讯作者: 阙云(1980-)，男，教授，博士，主要从事土壤渗流方面的研究和教学工作。E-mail: queyun_2001@fzu.edu.cn

中图分类号: P641.2；TU43

收稿日期: 2020-10-12

修回日期: 2021-03-05

刊出日期: 2021-11-15

Numerical simulation of water-gas two-phase displacement process in unsaturated granite residual soil

School of Civil Engineering, Fuzhou University, Fuzhou, Fujian　350108, China

More Information

Corresponding author: QUE Yun, queyun_2001@fzu.edu.cn

Received Date: 12 October 2020

Revised Date: 05 March 2021

Publish Date: 15 November 2021

摘要

摘要:
水流在非饱和土体中的入渗过程实质上是水在下渗的过程中驱替空气的两相流问题。为揭示非饱和花岗岩残积土水-气两相驱替动态渗流机理，选取福州某地原状花岗岩残积土作为研究对象，基于工业CT扫描图像与Level Set方法，研究了原状土样两相驱替的动态特征。结果表明：对于细观尺度水-气两相驱替模拟，Level Set法能很好地捕捉两种不混溶流体间的界面位置；水-气两相驱替过程存在大孔隙优先流特征，且“绕流”现象一般易于出现在孔隙成圆度较高处；两相渗流速度主要受孔道迂回度控制，笔直、较宽孔道，渗流速度相对较高，同时存在明显的“优势通道”，且随渗流时间增大以先急后缓的特征呈正相关变化，最大增速率为 10.77%，最小仅 1.90%；孔道横截面速度大小分布与孔隙结构有关，“回流”和“绕流”现象会使驱替速度骤降，降低幅度可达21.62%；驱替阻力最大出现在孔壁处，孔道越窄，阻力越大；驱替效率与驱替压差成正比关系，且初期加压增速效果显著，可达25.49%，后期仅为1.47%。该研究成果可丰富降雨型滑坡理论基础并预防灾害产生，具有重要的理论价值及工程意义。
- 非饱和花岗岩；残积土 /
- CT扫描切片 /
- 多孔介质 /
- Level Set /
- 水-气两相驱替
Abstract:
Infiltration of current in unsaturated soil is essentially a two-phase flow problem of water displacing air in the process of infiltration. The accuracy of traditional two-phase flow research methods cannot meet the needs of engineering, and it is not conducive to repetitive research. In contrast, the numerical simulation method of multiphase flow at the meso-scale can better simulate the whole dynamic process of water flooding. Mao Huan, Qren and others have achieved great results in the field of pore meso-scale research, but on the one hand, most of them focus on the study of rock multiphase flow, and there are some differences between the research object and the actual pore structure. On the other hand, the widely used pore network model method cannot directly show the change of particle velocity at any time and cannot present the phase interface movement state. In view of this, in order to reveal the dynamic percolation mechanism of water-gas two-phase displacement of unsaturated granite residual soil, this paper selected undisturbed granite residual soil in Fuzhou as the research object and studied the dynamic characteristics of two-phase displacement of undisturbed soil samples by using industrial CT scanning images and Level Set method. The results show that the Level Set method can properly capture the interface position between two immiscible fluids for meso-scale water-gas two-phase displacement simulation. The water-gas two-phase displacement process has the characteristics of large pore preferential flow, and the ‘low around’ phenomenon can easily appear in the higher ground of porosity roundness in general. The displacement rate is mainly controlled by the tortuosity of the channel, displacement speed is relatively high in the straight and wide channel. There is an obvious phenomenon of ‘preferential passage’, and its seepage time is positively correlated with the first rapid and then slow characteristics, and the maximum and minimum growth rate are 10.77 % and 1.90 %, respectively. The velocity distribution of the pore cross-section is related to the pore structure, and the phenomena of ‘reflux’ and ‘flow around’ cause the displacement velocity to drop sharply, whose decreasing degree can reach 21.62 %. The maximum displacement resistance appears at the hole wall, and the narrower the hole, the greater the resistance. The displacement efficiency is directly proportional to the displacement pressure difference, and the initial pressure growth effect is significant (up to 25.49 %, and only 1.47 % later). The research results can provide a theoretical basis for the study of the water migration mechanism of porous slopes, and also can enrich the theoretical basis of rainfall-induced landslides and are helpful in preventing natural disasters.
- unsaturated granite; residual soil /
- CT scan slice /
- porous media /
- Level Set /
- water-gas two-phase displacement

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图 1 现场取样

Figure 1.

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图 2 二维扫描切片

Figure 2.

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图 3 模型a—d二值化图像

Figure 3.

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图 4 模型b的计算几何模型及网格质量分布图

Figure 4.

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图 5 边界条件设定

Figure 5.

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图 6 水、气相占孔隙区域的面积随时间变化曲线

Figure 6.

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图 7 不同时刻水-气两相驱替过程动态示意图

Figure 7.

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图 8 不同时刻水-气两相驱替过程速度可视化图

Figure 8.

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图 9 不同孔道横截面速度分布图

Figure 9.

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图 10 不同时刻水-气两相驱替阻力分布情况

Figure 10.

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图 11 不同情况下驱替率曲线

Figure 11.

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表 1 材料属性

Table 1. Material properties

类别	界面张力/（N·m⁻¹）	密度/（kg·m⁻³）	动力黏度/（Pa·s）
水相	4.80×10⁻²	1000	1.01×10⁻³
气相	4.80×10⁻²	1.209	1.79×10⁻⁵

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表 2 两相流驱替研究结果对比

Table 2. Comparison of research results of two-phase flow displacement

类别	学者	吴丰等^[22]	冯其红等^[21]	高亚军等^[14]	张鹏伟等^[23]	本文
类别	对象	岩石	砂岩	岩石	孔隙模型	花岗岩残积土
驱替类型		气驱水	水驱油	水驱油	气驱水	水驱气
驱替可视化过程		微观指进	非平行推进	微观指进	优势渗流	回流、绕流
驱替速度		越靠近孔壁流速越小	速度越大采出程度越高	孔道中心流速最大，壁面流速最小	−	孔道中心流速并非最大，回流使流速骤降
驱替阻力		出口见气后，阻力减小	−	−	−	孔道越窄，阻力越大，最大值出现在孔壁
驱替效率		出口见气后效率不变	受孔喉、驱替速度、流体影响	−	−	与压差成正比，初期加压增速显著

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