Large-eddy simulation of suspended sediment transport in turbulent channel flow

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Joureal of Hydmdynamics 2013,25(1):48—55 DOI:10.1016/S1001—6058(13)60337—6 

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science ̄ottmaJ/1 001 6058 

Large—eddy simulation of suspended sediment transport in turbulent channel flow 

ZHU Hai,WANG Ling—ling,TANG Hong・wru College of Water Conservancy and Hydropower Engineering,Hohai University,Nanjing 2 1 0098,China, 

E—mail:redsea@hhu.edu.cn 

(Received April 22,2012,Revised June 12,2012) Abstract:The numerical simulation of the non—cohesive sediment transport in a turbulent channel flow with a high concentration is a challenging but practical task.A modified coherent dynamic eddy mode1 of the Large Eddy Simulation(LES)with a pick—up fun- 

ction is used in the present studv to simulate the sediment erosion and the deposition in a turbulent channel flow.The rough wall mode¨s used instead of the LES with the near—wall resolution to obtain the reasonable turbulent flow charactenstics while avoiding the high costs in the computation.Good results are obtained.and are used to analyze the sediment transport properties.The results show that the streamwise vortices play an important role in the riverbed erosion and the sediment pick—up,which may serve as guidelines for the sediment management and the water environment protection engineering. 

Key words:Large Eddy Simulation(LES),sediment suspension,pick-up function,turbulent channel flow 

IntrOducti0n The suspended sediment transport widely exists in lower reaches of rivers,estuaries,and coast areas, as an important issue for the water environment and the hydraulic engineering.The interaction between the sediment and the water is very complex,a great number of studies were devoted to solving this pro. blem theoretically,experimentally,and numerically. Clemens et a1.【 carried out the direct numerical simu— lation of the sediment transport in a turbulent channel flow with Reynolds number 2 880.which is far lower than that in natural rivers.Van RijnL刮applied the time..averaged advection..diffusion equations to simu.. 1ate the sediment transport by currents and waves with the help of numerous empirica1 parameters:his model was used in the DELFT3D.QJan et a1.【 used the Eulerian two.phase model together with the k一£ Project supported by the Nationa1 Natural Science Foun. dation of China(Grant No.5 1 1 79058).the State Key Program of National Natura1 Science Foundation of China(Grant No. 5 l 239003)and the Special Fund for Public Welfare of Water Resources Ministry(Grant No.2012010171. Biography:ZHU Hai f 1 986.1,Male,Ph.D.Candidate COrrespOnding author:WANG Ling.1ing, E—mail:wanglingling@hhu.edu.cn turbulence model to simulate the erosion of the loose beds by the submerged circular impinging vertica1 tur- bulent iets.Huai et a1.L斗。used the RNG k— turbu— lence model to simulate the sandy bed erosion caused by the 2一D vertical 1et and the results of their new mode1 agree well wim the experimental data but their main concern is the morphological change rather than the suspended load transport.The erosion process of the riverbeds is largely due to the bursts of the wall turbulence.that is.the effect of the sweep and the eje- ction.so the RANS models are not adequate to des- cribe this phenomenon.In fact,even the unsteady RANS methods can not accurately describe the highly intermittent flow events.Recently,the large eddy simulation serves as a very popular tool to simulate the environmental flows.such as the open channel flow with vegetation,me submerged iets,and the sedi- ment transport because of its ability to capture the an— steady motion of the flow field accurately with the support of the ever improved computer capabilities.A traditional Smagorinsky model of LES was employed by Suzuki et a1. to study the intermittent sediment concentration under the environment of breaking waves.Li et a1.L。 compared the results of the Dynamic Smagorinsky.Lily Model(DSLM)and the Dynamic Kinetic energy Subgrid—scale Model(DKSM)in the simulation of the interaction between the wal1 iet and 

一 the of-fset iet.Chou and FringerL/j modeled the dilute suspension using the Large Eddy Simulation(LES) with a dynamic mixed model at high Reynolds numbers.Zedler and Street applied a simple Smagorinsky model to simulate me detailed sediment dynamics in a channe1 flow over ripples;they also used the LES to simulate the sediment transport over ripples in an oscillatory flow. AIthough good results were obtained.these stu— dies concem only the low sediment concentration wim the interaction between particles ignored,and without consideration of the effect of the sediment on the flow field.In the present study.a modified coherent dyna. mic eddy model of the LES is employed,in which the turbulent coherent structm'e O is considered to dete— rmine the turbulent eddy viscosityL ….An empirical damping function is used to decrease the turbulent eddy viscosity when the sediment concentration is high to make the simulation results more realistic in both the flow field and the concentration field.More— over,the model was successfully applied to simulate iets,waves,and turbulent channel flow,showing that it is superior to other traditional LES models ii.In