粗糙元对单裂隙渗流影响的格子Boltzmann方法模拟及分析

Simulation and analysis of the effect of roughness elements on fluid flow through single fracture based on lattice Boltzmann method

岩体单裂隙中的粗糙结构会对流体流动性能产生一定影响,但实际粗糙结构复杂无序,很难通过直接研究认识到其作用机理.本文在单裂隙中构造了参数化的人工粗糙元,并基于格子Boltzmann方法自行编写了程序,对单裂隙中不同间距、高度和数量的粗糙元作用下的渗流场进行数值模拟,定性分析了速度场、压强场、角速度场的变化规律;在定性分析的基础上提出了等效黏度的宏观描述方式,定量分析了粗糙元对等效黏度的影响.结果表明渗流场中粗糙元的存在造成了一系列涡旋,增大了等效黏度;涡旋本身具有局域性但作用的范围很大;在低速渗流条件下这些粗糙元附近的涡旋互不影响,可以划分成若干个相互独立的含涡区,这种划分对于理解涡旋对等效黏度的影响有很大帮助.

Establishing accurate seepage model for single fracture in rock is meaningful for not only scientific but also engineering problems.Rough structures must be sufficiently considered,because it has significant impact on the behaviors of fluid flow through single fracture of rocks.But the actual rough structure is generally too complex to have a full and detailed description,consequently,direct studying fundamental mechanisms via such a model is nearly impossible.Under such a situation,the artificial roughness element,which can be modeled parametrically,is implemented to describe the single fracture in this paper.In order to explore the impact mechanism of the rough structure on fluid flow through single fracture of rock,codes based on lattice Boltzmann method（LBM）,which was verified to reflecting more flow details,are developed to simulate the seepage field in a single fracture with roughness elements having different intervals,heights and amounts.Fields of velocity,pressure,angular velocity are analyzed quantitatively,and some new observations are presented.Based on the above quantitative analysis,a new descriptive method,the equivalent viscosity,is proposed.Subsequently,the relationship between roughness element and equivalent viscosity is investigated quantitatively.The results show that,vortex is the main influential factor of flow reducing effect of roughness elements,and vortex itself is regional but has influence on a large region of field.Under the condition with low speed fluid flow,the vortex near roughness element can be divided into several regions which are mutually independent.The results provide a theoretical support to the understanding of flow phenomena in roughened single fracture and are helpful for establishing effective seepage model of single rough fracture.