阶梯布置对溢洪道尾水二次消能及流态影响研究

Study on the Impact of Step Layout on Secondary Energy Dissipation and Flow Pattern of Spillway Tailwater

云南省凤庆县大摆田水库溢洪道出口坎式底流消力池和下游尾水渠之间需要进行二次消能,同时在阶梯消能段通过40°弯道衔接,以适应地形变化。通过水工模型试验研究,原方案出池水流经过阶梯弯道后,平面上形成明显的Z形折冲水流,30年一遇时弯道末端左侧水流临边流速达9.97 m/s,已经威胁到左岸山体顺坡岩层的稳定。阶梯后移的修改方案能够有效改善弯道内水流流态,在此基础上,提出将原阶梯体型减小(2.50 m×1.50 m减小至1.00 m×0.60 m)的改进方案,以避免在经常发生的小流量洪水情况下,阶梯位置出现跌落水流。研究成果表明:改进后的弯道阶梯消能组合方案使得小流量洪水情况下消力池下游尾水渠沿程横断面水深分布相对均匀,水流流态改善明显,解决了常遇洪水下泄时水流平顺归河问题。

A secondary energy dissipation is required between the sill underflow stilling basin and the downstream tailrace at the outlet of the Dabaitian Reservoir spillway in Fengqing County,Yunnan Province.At the same time,the stepped energy dissipation section is connected through a 40°bend to adapt to the change of terrain.Through the hydraulic model test research,based on the original plan,after the water flowing out of the stilling basin passes through the stepped bend,an obvious Z-shaped folded water flow is produced on the plane.When it occurs once in 30 years,the water velocity on the left side of the bend reaches 9.97 m/s,threatening the stability of the rock formations along the slope of the left bank.The modified plan of step backward movement can effectively improve the flow pattern in the bend.On this basis,an improved plan to reduce the size of the original step(2.50 m×1.50 m to 1.00 m×0.60 m)is proposed to avoid falling water flow at the location of the step in the case of frequent small-flow floods.The research results show that in the improved stepped energy dissipation combination for bend,the water depth distribution along the cross section of the tailrace downstream of the stilling basin is relatively even in the case of small-flow floods,and the flow patten is improved significantly,so the water flowing back to the river smoothly is realized under frequent flood discharges.