Numerical Study Of Effect Of Roughness On Water Flow Through A Single Fracture

Study of the water flow through rough fracture is a big issue in groundwaterpollution prevention, deep underground engineering and the geological disposal ofradioactive nuclear waste. However, due to the strong spatial variability of thebedrock fracture media, the water migration in fracture media is very complex. Atpresent, both theoretical research and practical application have emerged manyproblems. On the basic of the summarization of the related literature, a numericalmodel is used to study the effect of roughness on the water flow through a singlefracture. Under the guidance of a single variable principle, Gambit is used to createa numerical model of the rough single fracture and it also set up a smooth flat-panelcracks, triangular rough surface, rough surface trapezoidal, rectangular roughsurface and sinusoidal rough surface.52numerical models are setup, including thedegree of absolute roughness raised to1,2and4mm, respectively, the ratiobetween absolute roughness and the rough gap is:1:1,1:2,1:3and1:4. The Fluentis used to solve the52kinds of model, by being used reinforced mesh in the nearwall region, under the conditions of the Reynolds number (Re) ranging from1to3200. Subsequently, the distribution of fluid fields in different rough fractures issimulated and analyzed．The result can be concluded as below：(1) By the analysis of y+and residuals, the enhanced wall function, realizablek model in Fluent software can be used to simulate the rough single fractureflow.(2) By the analysis of the velocity contours, velocity contour map, flow chart,Diversion characteristics in the rough fracture are decided by the degree of roughelement density: the ratio between absolute roughness and the rough gap, absoluteroughness, the geometric profile structure of roughness：1）the smaller the ratio between absolute roughness and the rough gap is, thegreater the impact on the water flow line will be.2) The lager the absolute roughness is, the larger the degree of flow linebending will be.3) The closure of the rectangular roughness on the flow is the most obvious,the trapezoidal roughness takes the second place, and the sinusoidal roughnessfollows, which shows that the greater the angle of the flow into the roughness, the more obvious the closure and vortex will be.4) The bending degree of the water flow line above Sinusoidal roughness is thelargest,followed by triangle roughness and rectangular roughness is the smallest,which shows that the greater the angle of the flow into the roughness is, the lowerthe bending degree will be.(3) According to the relationship among friction factor, unit discharge, meanvelocity, hydraulic gradient (v-J) and the analysis of critical Reynolds number, thetends show the friction factor based on numerical simulation is smaller thanthose that are calculated by other formulas,however, the unit discharge isrelatively larger. The tend of v-J relationship, under the condition of largeReynolds number, shows a non-linear phenomenon of the Non-the Darcy andForchheimer equation did the best job,followed by Izbash equation; The analysisof the critical Reynolds number (Rec) shows that Recof the smooth flat is about2400, the rough fracture Recis about80,Along with the increase of the roughnessRecwill decrease.