单孔双窄缝消能工收缩比对水力特性影响研究

Influence of contraction ratio of double narrow slot buckets energy dissipator on hydraulic characteristics

单孔双窄缝消能工在高水头、大流量、窄河谷的水利工程中具有一定的推广价值,但在应用过程中发现中墩迎水面容易受水流冲击而破损,而收缩比对此现象和消能效果影响较大。采用TruVOF方法及RNG k-ε紊流模型进行三维数值模拟,研究在不同来流Fr数下收缩比对水舌流态、消能率、河床底板及挑坎收缩段压力分布变化规律的影响。结果表明:数值模拟与物理模型试验结果基本吻合,可通过调整收缩比β获得合适的高坎中墩水深来减弱高速水流对中墩迎水面的冲击;当β=0.3时,下游河床底板峰值压力P_(max)最小,且峰值压力核心区与传统窄缝相比前移60 m;β<0.3时,P max随着β的减小反而开始增大,而消能率随之减小,同时在挑坎收缩段中部附近位置出现冲击波交汇点,且流道内各断面中线压力沿水深分布在压力最大值前后其规律不同,与宽尾墩类似。虽然来流Fr数对分流比影响较小,但当2.43<Fr<2.82时,各体型方案的分流比k q增大幅度较大,导致双窄缝体型河床底板压力变化幅度较明显。

Double narrow slot buckets energy dissipator in flood discharge of high head,large discharge and narrow valley has certain application values,but the facing water surface of the middle pier is easy to be damaged by the impact of water flow during operation,and the contraction ratio has a greater impact on this situation and the energy dissipation.Therefore,numerical simulation was carried out by using the TruVOF method and RNG k-εturbulence model to study the influence of the contraction ratioβbon the jet flow pattern,energy dissipation rate,pressure of the scour pool bottom and the pressure distribution in the bucket contraction section under different inflow Froude number Fr.The results showed that the numerical simulation results were basically consistent with the physical model test,and the proper water depth of the middle pier can be obtained by adjusting the contraction ratioβto reduce the impact of high-speed water flow on the middle pier.Whenβ=0.3,the peak pressure P max of the downstream riverbed floor was the least,and the peak pressure core area moved 60 m forward compared with the traditional narrow slit bucket.Whenβ<0.3,P_(max)began to increase with the decreasing ofβ,and the energy dissipation rate decreased.Meanwhile,the confluence location of shock waves appeared near the middle of the contraction section of the bucket,and the pressure distribution along the water depth at the middle line of each section in the flow channel was different before and after the maximum pressure appeared,which was similar to the flaring gate pier energy dissipation.Although Fr had little influence on the discharge ratios,when 2.43<Fr<2.82,the discharge ratio of each type scheme increased significantly,resulting in a significant variation in the floor pressure of the double narrow slot buckets.