Simulation Study On The Effect Of Roughness Element And Its Density On Flow Characteristics In A Single Facture

Study on groundwater flow characteristics of bedrock fracture has become a veryimportant research direction of environmental and hydrological geology field. A singlefracture is a basic element of fractured media, Fracture structural plane roughness is animportant index of hydraulic characteristics of bedrock fracture water. But the effectivedescription of roughness of fracture surface is difficult to study bedrock fracture water.In this paper, with Fluent6.2.2simulation software, we simulate water flow in fracturedmedia in conditions of different roughness element shapes and different density, andanalyzes the relations between related parameters, main research achievements andresults are as follows:(1) Through the analysis of velocity distribution image of different fractures, We candraw a conclusion as follows: The shape of the rough element has different degree ofinfluence on water flow in fractured media:rectangular> sine> triangle.In the fracturewith different roughness element density, the more the roughness element density, themore effect on water movement. The turbulence phenomenon is also increasinglyobvious. Fissure water pressure distribution also has the regular pattern.(2)Fitting the relationship between average velocity V and hydraulic gradient J withthe Darcy equation, Forchherimer equation and Izbash equation, We can draw theconclusion that, the V-J curve relationship is nonlinear obviously.When the flow rate issmall, the Forchherimer equation and the Izbash equation can fit the relationshipbetween average velocity and hydraulic gradient well. With the increase of flow rate,the fitting effect of Forchherimer equation can be better than that of the Izbash equation.quadratic term coefficient of the Forchherimer equation increases with the increase ofroughness element density. In the the Izbash equation, the coefficient m of averagevelocity v increases first and then decreases, with the increasing of rough elementdistribution density, corresponding to the shape of triangle and sine roughness element.The m value increases with that in that of rectangular roughness element.(3)The differences of per unit width discharge between calculated values with cubiclaw and that with simulation increase with the increasing of J. The actual value of perunit width discharge reduced certain multiple than that with cubic law. The minificationof that corresponds to different roughness element density. The exponent values ofaverage aperture are more than3in different fractures, which belongs to Super cube law.And the value of m decreases with the increase of the average aperture (4)The critical velocity (Jv=Ji) increases with the increasing of the aperture. Thecritical velocity, with increasing of roughness element density, increases at first andthen decreases.(5)Corresponding to different fractures, we can draw that the further the distancefrom the entrance end, the greater and increases more rapidly the value of permeabilitycoefficient K. The correlation permeability between the permeability coefficient K andthe corresponding horizontal distance L increases at first and then decreases, as theincrease of roughness element density.(6)According to the curve between Reynolds number Re and resistance coefficient λin different fractures. we can see that When the flow rate is small, the λ value decreasessharply with the increasing of Re, and a decreasing trend slowed down and graduallyclose to the horizontal line, as the Re is more than about15.The λ value decreases withthe increasing of roughness element density, corresponding to the same Re value.(7)Introducing the concept of the deviation coefficient C, we can draw a conclusionfrom the C-Re curve that the value of C increases with the increasing of Re in differentfractures. The C increases with increasing of roughness element density, correspondingto the same Re value.