Flow Field And Sediment Transportation Simulation Of Bend With Inserted Transition Curve

When the water flows through the bend, the liquid particle is simultaneously subjected to the action of both gravity and centrifugal inertia force, combined with the longitudinal speed of the main stream, the secondary flow was performed in the cross-sections perpendicular to the flow direction and thus formed spiral flow. The spiral flow will cause the lateral transport of river sand and the transverse gradients which the water surface of concave bank is higher than convex bank were formed, thus the mainstream deviates from the center line to form the spiral flow. Therefore, the study on the motion law of bend flow is of great significance to the river development, sediment protection and river evolution.Inspired by the curve setting at the turning place of the road, in this study, the transition curve was inserted in the river bend. By using MIKE 3 hydrodynamic model and sediment transport model under two schemes which are clean water fixed bed condition and clean water scouring condition, the hydraulic characteristics and sediment transportation factors in 120?single curve bend, slow-round-slow curve bend and convex symmetrical bend were studied, and the effect of different transition factors "A" (present in slow-round-slow curve bend and convex symmetrical bend) on bend flow is analyzed, too.The results are as follows:(1) Channel bend with inserted transition curve performed well in reducing bend water surface super elevation, transverse gradient and improved the twist rate of bend flow. Above all three bend forms, slow-round-slow bend is the most effective scheme to improve water surface morphology.(2) The velocity in concave bank near river bed of the bend with inserted transition curve is less than that of single curve bend. In the inlet section and curved top section of convex bank,the near-bed velocity is significantly decreased than the single curve bend scheme, showing that the bend with inserted transition curve can reduce the near-bed flow velocity. In the concave side, the erosion of transition curve inserted bend is much smaller than the single curve bend,the deposition of transition curve inserted bend in the convex side is also significantly smaller.It indicates that the bend with inserted transition curve can obviously reduce the scouring and silting effect of sediment.(3) Through the analysis of different hydraulic and sediment transportation characters,the effect sorting of three bend forms in improving the water flow regime are: slow-round-slow bend > convex symmetrical bend > single curve bend.(4) The improvement effect of transition curve is not only depend on the length of the inserted transition curve, but also related to the bend curvature. The greater the transition factor,the better the effect.