Three-dimensional Numerical Simulation Of Bend Flow Inserting The Transition Curve

Meandering rivers are one of the most common river morphology of nature.Redistribution of velocity,circulation flow and transverse slop all these special flow phenomena will appear because of the complex 3D flow in bend.When water current passes the curved section under the together function of centrifugal inertial force and gravity,the secondary flow in the cross-section of vertical flow is existed,superpositioned with longitudinal velocity,thus spiral flow is structured.The water surface is higher in concave bank,the bed surface is flowing from convex to concave bank,diving to convex bank,turning to the surface of the water flow to the concave bank,the cycle will be repeated again and again,then the concave bank is soured and convex bank deposited.Therefore,the study on bend flow,which plays an important role in hydraulic engineering,is widely used in river regulation project,harbor construction,water diversion and sediment prevention,anti-scour of bridge pier and improvement of river navigation.In this paper,three kinds of curves: basic symmetric bend,asymmetric A bend and asymmetric B bend were introduced to decrease the impact force of load and centrifugal force.To study the optimal bend to prevent scouring along the river bed,dike and feet of the dike,a three-dimensional numerical simulation under two models: clear water-fixed bed and clear-water scouring had been done,and the HD module and ST module in Flow Model FM of MIKE 3software had been used to analysis the water surface,flow shape and river bed change processes among three types of bends.Through numerical analysis some results are concluded:(1)The ultra-high and horizontal surface slope of the three bend with inserting curves are significantly reduced compared with the round bend,and the decreasing range of basic symmetric bend is especially obvious.(2)The near bed current velocityof the three bend with inserting curves are significantly reduced compared with the round bend and so as the lateral sediment transport,which shows that bends with inserting curves could significantly decrease the lateral sediment transport.(3)The deep groove of these three inserted with graded curves is obviously shallower than the round bend.(4)These three bend with inserting curves could improve the water flow regime,delay the location of scouring point,shorten the erosion length of concave bank.(5)From the prediction and water surface result,the sorting of improving water surface and decrease topography of scouring and silting from big to small was basic symmetric bend>asymmetric A bend >asymmetric B bend>round bend.