摘要
为了探究琴键堰在淹没出流条件下的泄流情况及对淹没效应的敏感性,该研究在矩形水槽中对四种琴键堰基本体型(A型:上下游均倒悬;B型:上游倒悬;C型:下游倒悬;D型:上下游均无倒悬)进行了物理模型试验,分析琴键堰在淹没出流条件下的流态随下游水位的变化过程,得到其上下游堰上总水头之间的关系及淹没系数,并进一步分析四种琴键堰对淹没的敏感性以及比较四种琴键堰在淹没出流条件下的泄流量和泄流效率。试验结果表明,随着下游水位的壅高,四种琴键堰堰后依次出现了淹没后的冲击射流、破碎(表面跳跃)、表面波和表面射流流态;在来流量相同的情况下,C型和D型琴键堰在淹没系数S≥0.6时,逐渐发生淹没,且其流量折减系数随淹没系数的增大而减小,而B型和A型琴键堰分别在S≥0.15和S≥0.2时提前进入淹没状态。四种不同体型琴键堰的临界淹没度(S_(m))分别为:A型0.5、B型0.3、C型0.7、D型0.65。对比看来,仅具有上游倒悬结构的B型琴键堰对淹没最为敏感,其次是具有对称倒悬结构的A型,而向下游的倒悬结构可以延缓上游的淹没;四种不同类型琴键堰的淹没泄流效率受“对淹没的敏感性”和自由出流泄流效率两个方面的综合影响。研究成果可为完善琴键堰堰流理论、推动其在明渠及河道中的应用提供技术支撑。
Downstream submergence can determine the relationship between the water head and the discharge capacity of the weir,once the tail water exceeds the weir crest elevation in the channel application of weirs.This study aims to explore the discharge characteristics of Piano Key Weirs(PKW)under submerged flow conditions.A series of physical tests were carried out for the four types of PKW in a rectangular flume.The relationship between the total head on the upstream/downstream and the submergence coefficient of PKW flow was obtained in the variation process with the downstream water level under the submerged flow.The flow reduction coefficient and dimensionless water head method were also used to determine the relationship between the total head and flow reduction coefficient of PKW and the submergence coefficient.An analysis was made on the sensitivity of four PKW types to submergence.The fitting was performed on the formula of submergence flow reduction coefficient of PKW.The reverse standardized upstream water head method was utilized to compare the hydraulic efficiency of four PKWs under submerged conditions.The experimental results show that the impinging jet,breaking(surface jumping),surface wave,and surface jet flow after the four kinds of PKWs appeared in sequence,as the downstream water level rose.Specifically,the type C and D PKWs were gradually submerged at the submergence coefficient S=0.6,when the upstream discharge was constant.The discharge reduction coefficient decreased with the increase of the submergence coefficient.The type B and A PKWs entered the submergence state in advance,when S≥0.15 and S≥0.2,respectively.Correspondingly,the critical submergence S_(m) of four types of PKWs were:type A 0.5,type B 0.3,type C 0.7,and type D 0.65,respectively.In contrast,the type B PKW with only upstream overhang structure was the most sensitive to the submergence,followed by type A with the symmetrical upstream and downstream overhang structure,while the overhang structure towards the downstream was delayed the upstream submergence.Different PKWs varied differently under the downstream water level,which was mainly related to the overhang length of the upstream and downstream of each model.The longer the overhang in the upstream was,the slower the slope of the outlet key was,and the more likely it was to be submerged.In the type C and D PKWs with the longest downstream overhangs,the water nappes flowing through the inlet key under the action of the inertia of the water flow,pushed the downstream water flow to a position far away from the PKW crest,thus delaying the effect of submergence.Finally,the calculation formula of submerged discharge coefficient was fit to further compare the discharge capacity and hydraulic efficiency of four types of PKWs under submerged conditions.It was found that the discharge efficiency of type C and D PKW was lower than that of type A PKW,and the efficiency of type B was the highest when the submerged coefficient S was relatively small.There was a reverse variation in the discharge efficiency of each type of PKW,when S≥0.7.The submerged discharge efficiency of four types of PKW depended on the comprehensive influence of“sensitivity to submergence”and free-flow discharge efficiency.The findings can provide technical support for the optimal weir flow of the PKW in the application of open channels and rivers.
作者
李珊珊
李国栋
姜铎
沈桂莹
Li Shanshan;Li Guodong;Jiang Duo;Shen Guiying(State Key Laboratory of Eco-Hydraulics in Northwest Arid Region,Xi’an University of Technology,Xi’an 710048,China;Yulin Silt Dam Construction Center,Yulin 719000,China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2022年第9期64-72,共9页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家自然科学基金项目(51579206)
陕西省水利厅科技计划项目(2017slkj-17)
国家自然科学基金项目(52079107)。
关键词
水力学
流量
堰
淹没系数
无量纲水头
泄流效率
hydraulics
discharge
weirs
submergence coefficient
dimensionless water head
discharge efficiency
