岩体裂隙面粗糙度对其渗流特性的影响研究

为了研究岩体裂隙面的粗糙程度与渗流机制间的相互关系,将裂隙沿长度方向均匀分割成若干段,通过设置每一段末端的随机高度,生成两侧对称的粗糙裂隙面。基于格子Boltzmann方法,采用不可压缩流体的D2G9模型,验证了经典的Poiseuille流,计算了不同相对粗糙度岩体裂隙的渗流特性,讨论了裂隙面粗糙度对渗流流态的影响。研究结果表明:裂隙结构壁面对流体的阻碍作用,使得流体在壁面附近的流动产生急剧调整,同时随着裂隙相对粗糙度的增加,在裂隙隙宽急剧变化的部位,局部伴随着旋涡的形成,导致流体内部摩擦阻力作用增大。在单位时间截面渗流流量及每一段平均隙宽相等的条件下,将本数值解与多平行板理论解进行了对比,对于相对粗糙度δ=0.01674的裂隙方案,由于多平行板理论解忽略了粗糙裂隙隙宽变化而引起的局部压降,其裂隙中线处压降产生的最大误差达到15.2%。当相对粗糙度较小时,裂隙中线处的压力与光滑平板流相类似,近似呈线性变化。随着裂隙相对粗糙度增大,压力变化偏离直线方向,且在断面由窄突然变宽的部位,压力变化偏离线性尤为显著。

Influence of roughness of rock fracture on seepage characteristics

In order to study the relationship between surface roughness of rock fracture and seepage mechanism, the rock fracture is divided into several segments along length direction, and the symmetric rough fracture surface is generated by setting random height at the end of each segment. Based on the D2G9 model, which is used for simulating incompressible fluid, the classic Poiseuille flow is verified using the lattice Boltzmann method, the seepage characteristics of rock fracture with different relative roughnesses are calculated, and the influence of surface roughness on the flow state of fluid is discussed. The results show that the fracture wall blocks the flow of fluid, and flow state near wall changes dramatically. At the same time, with the increase of the relative roughness, there are vortices in the local area, where the changes of fracture width are dramatic, which induces the increase of internal friction in the fluid. Under the equal flow discharge of section in unit time and average fracture width, the present numerical solution is compared with the theoretical one of multi-parallel plate. Because the multi-parallel plate theory neglects the partial pressure drop caused by changes of fracture width, the maximum error of the pressure drop in the middle section is 15.2% less than the numerical solution for fracture scheme with relative roughness δ=0.01674. When the relative roughness is small, the pressure in the middle of fracture is similar to that of the smooth plate model, and the trend is almost linear. The pressure deviates from the line direction with the increase of relative roughness, and the changes are larger at the section, where the fracture width changes from narrowness to broadness suddenly.