基于TOUGH2和FLAC3D的水-气二相流-固耦合模型

要实现饱和-非饱和土体的水-气二相流-固耦合作用的数值模拟,关键是如何实现渗流场与应力场的耦合,目前,松弛耦合方法不仅精度能够满足一般的工程要求,而且求解方法易于实现,是多相流-固耦合问题研究的主要方向。本研究根据松弛耦合原理,利用TOUGH2/EOS3来模拟水-气二相渗流过程;利用FLAC3D来模拟土体变形;基于水-气二相渗流过程与力学过程的相互影响,给出饱和度-密度、孔隙水压力和气压力-有效应力、体积应变-孔隙率、孔隙率-固有渗透率,以及孔隙率-毛细压力等状态变量之间的耦合关系式;利用C++控制TOUGH2、FLAC3D在流固耦合过程中的有序运行并利用耦合关系式传递相关状态变量,以实现对水-气二相流-固耦合作用的模拟。利用该模型对一现场压气试验进行模拟,通过模型计算值与实测值的对比,验证了模型的准确性和有效性。

A Loose-Coupled Water-air Two-phase Fluid-Solid Model Based on TOUGH2 and FLAC3D

How to couple fluid flow and mechanics is very crucial in numerical simulation for water-air two-phase fluid-mechanical interaction in saturated-unsaturated soil. The loose coupling has the advantages of being relatively simple to implement and with higher accuracy. Thus the loose coupling algorithm is one of the main ways for coupled fluid flow and mechanics modeling under multiphase flow conditions. This paper presents the loose coupling scheme for simulating water-air two-phase fluid-mechanics interaction, in which TOUGH2/EOS3 is employed to model the water-air two-phase flow process, FLAC3D is conducted to analyze the mechanical process, and two codes are linked and sequentially executed through external coupling modules by C++ computer language. The coupling relationships for linked TOUGH2-FLAC3D simulations are presented, including relationship between saturation and soil density, effective stress function depending on both liquid and gas pressure, corrections of porosity, permeability, and capillary pressure for changes in stress. The accuracy and efficiency of linked TOUGH2-FLAC3D simulator are verified by simulating an in-situ air flow test in Essen and comparing the measured and calculated values of surface placement and air losses.