外文翻譯--橋墩周圍的紊流和沖刷比尺效應(yīng)的cfd建模研究（原文）

1、CFD modeling of scale effects on turbulence flow and scour around bridge piersWenrui Huang a,*, Qiping Yang b, Hong Xiao ba Department of Civil and Environmental Engineering, Florida A 2002] indicate that it is difficult

2、 to verify the scour equation with field data obtained from largebridge piers. In this study, computational model simulations using a 3D CFD model were conducted toexamine scale effects on turbulent flow and sediment sco

3、ur. For the large-scale model, the physical scaleand boundary velocity were set up from the small scale model based on the Froude similarity law. Resultsof flow and sediment scour were obtained from two different approac

4、hes: (a) Froude similarity which iscommonly used in physical modeling and (b) full scale 3D CFD modeling. Unlike physical modeling inwhich the effect of turbulent Reynolds number is ignored, the CFD model employs a 2nd o

5、rder turbulentmodel to calculate turbulent velocity and sediment scour. Effects of scale on turbulence flow and sedimentscour were investigated by comparing different results obtained from a full scale numerical model to

6、 thosederived from the Froude similarity method.? 2008 Elsevier Ltd. All rights reserved.1. IntroductionThe threat of local scour around bridge piers has been known for many years. According to Richardson et al. [16], th

7、e local scour around bridge piers is one of the most common causes of bridge failures. It has been observed that in the free surface flow around a bridge pier, downwash motions, horseshoe vortices and vortex shading are

8、formed and the turbulence is intensified in front of, around and behind the piers. In addition, a uniquely shaped scour hole on the loose bed around a pier is observed. Experimental stud- ies have found that both the flo

9、w and the sediment transport pro- cesses during the scour hole development are highly complex. The study of local scour around a bridge pier started with labo- ratory experiments. Laursen [10] investigated the relationsh

10、ip of clear water scour in a long contraction as a function of geometry, flow, and sediment. He developed an equation for the equilibrium depth of scour for a pile or abutment. Shen et al. [17,18] conducted 21 experiment

11、s using a single cylinder diameter and sediment size, but varying the hydraulic conditions (water depth and the depth averaged flow velocity) to include both clear water and live bed conditions. They developed the empiri

12、cal equation for scour depth as a function of time for a pile of diameter, D, in a flow with a depth averaged velocity, V, and an upstream water depth, y0. Cunha [5]found that the Shen et al. [18] model was based on a na

13、rrow range of flow and sediment conditions and therefore is probably not very well suited to practical applications. The complete absence of sed- iment size as a factor in the model makes it difficult to any appli- catio

14、n of the model to conditions other than those in his experiments. Breusers [3] carried out experiments using piles with D = 5 and 11 cm, water depths of 15, 25, and 50 cm and sand par- ticles with d = 2 mm. Experiments w

15、ere carried out for fixed values of U0/U0c (U0c = critical water velocity for the initiation of bed movement). Totapally et al. [19] examined the temporal variations of local scour under steady flow and using stepped hyd

16、rographs. They concluded that a logarithmic equation represented the varia- tion of scour with time better than a power equation and ques- tioned the existence of an equilibrium depth, maintaining that scour will continu

17、e with time though at a greatly reduced rate. Graf et al. [8] investigated the flow patterns in planes upstream and downstream of a cylinder and vertically in the scour hole using an acoustic-Doppler velocity-profiler (A

18、DVP). They found that the shear stress was reduced in the scour hole as compared to the ap- proach flow but that the turbulent kinetic energy was very strong at the foot of the cylinder on the upstream side. The turbulen

19、t ki- netic energy was also very strong in the wake behind the cylinder. In addition to experiments, numerical simulations based on computational fluid dynamics (CFD) have been widely used to study the turbulent flow and

20、 sediment transport around a pier. Most models for predicting sediment transport are based on a0045-7930/$ - see front matter ? 2008 Elsevier Ltd. All rights reserved.doi:10.1016/j.compfluid.2008.01.029* Corresponding au

21、thor. Fax: +1 850 410 6236.E-mail address: whuang@eng.fsu.edu (W. Huang).Computers & Fluids 38 (2009) 1050–1058Contents lists available at ScienceDirectComputers & Fluidsjournal homepage: www.elsevier.com/locate/

22、compfluid15 cm thick layer in the flume bed. The numerical simulation was set up according to the experimental conditions. The geometric setup for the numerical simulation is given inFig. 1 and the grids of the computati

23、onal domain generated by GAMBIT are shown in Fig. 2. The grids near the cylinder are gener- ated more densely because the flow pattern in the region is more complex. The inlet boundary was placed at the left side of the

24、pier, 10R (R is the radius of the pier) from the pier center. The type of the boundary was set as velocity-inlet. A uniform velocity of 0.067 m/s in accordance with the experiment was applied on the inlet bound- ary. The

25、 outlet boundary was placed at 10R right to the center of the pier. The type of boundary was set as outflow where zero-gra- dient boundary conditions are used. The velocities are set equal to the values in the elements c

26、losest to the outflow. At the down- stream outlet, the normal gradients of all dependent variables are set to zero, i.e., variables at the downstream end are extrapo- lated from the interior domain. The wall boundary was

27、 set at the top of the water surface in order to simplify the simulation. The two-phase (water and sand) Eulerian model was used in order to simulate the local scour and simplify the problem. The top layer is phase water

28、 and the bottom layer is phase sand (Granular). It was observed that the maximum scour depths occurred at the midpoint of the upstream face of cylindrical pier. The grains at the upstream side of the piers were observed

29、to be dislocated due to horseshoe vortices. As the scour hole enlarged with respect to time, the strength of the horseshoe vortices weakened, causing a smaller rate of scour development, and the scour depth approached an

30、 equilibrium value asymptotically. The contours around the cylindrical pier obtained at the end of 5 min of test duration are shown in Fig. 3. The results of numerical model simulations of local scour for the bridge pier

31、 at T = 5 min are given in Fig. 5.5. the maximum scour depth and the deepest scour hole in front of the cylinder are reasonable in good agreement with those from the experiments conducted by Yanmaz et al. [23]). Itindica

32、tes that the computed scouring pattern is in good agreement with physical observations.4. Scale effects on modeling turbulence flow in solid bottom conditionIn order to study the scale effects on turbulence flow around a

33、 bridge pier, two different sized models were set up for numerical simulations. The small-sized model stands for the physical model and the large-sized model stands for the prototype. They are geo- metrically similar. Th

34、e condition boundaries were set up according to the Froude number similarity. Hence, they meet the require- ments of the geometric similarity and the Froude number similar- ity. However, this model is distorted because t

35、hey do not meet the requirements of the Reynolds number similarity. The aim of the numerical simulation is to check the difference of flow field around a bridge pier when the simulation results of the small-sized model a

36、re used to predict the situations of the large- sized model according to the similitude theory. To simplify the problem and avoid the feedback of the sediment move, a one- phase (water only) model was employed in the gro

37、up of simula- tions. The 3D computational fluid dynamic model package, FLUENT CFD package, was utilized to test the scale effects on turbulence flow around a bridge pier in the simulations.4.1. Geometric setupThe geometr

38、ies of the small-sized and large-sized models were used for numerical simulations. Their dimensions were setup as in Table 1. They are geometrically similar and the scale ratio of length is Lr = 25. Fig. 1. The geometric

39、 setup for bridge pier scour simulation.Fig. 2. Computational grid for 3D numerical simulation of local scour around a bridge pier.-4 -3 -2 -1 0 1 2-3-2-10123y-direction (y/R)3736353534343332302928343231302828x-directio