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