琴键堰泄流能力影响因素与计算分析研究

近年来特大洪水和超标准洪水频繁发生，已建水利工程泄流能力不足问题日益突出。琴键堰在适当低水头条件下具有高效泄流效率。归纳了琴键堰主要结构参数对其泄流能力的影响及最佳取值，总结了琴键堰流态对泄流能力的影响，分析了琴键堰发生低水头行为的条件参数。通过对比现有琴键堰泄流能力估算公式，并结合国内外已有试验数据，采用遗传算法拟合推导了基于溢流堰轴线长度L、堰宽W、堰长B、堰高P、进出水宫室宽度比W_i/W_o及上下游倒悬长度比B_o/B_i流量系数计算式，整体误差小于6%。该式计算简单，适用于琴键堰整体泄流能力估算，可根据实际需求选取合适的估算公式。琴键堰主要结构参数的最佳取值及泄流能力的计算方法可为超标准洪水条件下泄流建筑物设计或改建提供估算依据。

Calculation analysis on the discharge capacity of Piano Key weir and relative influencing factors

In recent years, the problem of insufficient discharge capacity of the existing hydraulic projects has become more and more serious due to the frequent occurrence of extreme floods. The Piano Key weir has a high-efficiency discharge capacity when the water head on the weir is properly low. The calculation analysis of its discharge capacity has great practical value. The discharge capacity is related to the main structural parameters of the Piano Key weir and the water head on the weir. In this study, the influencing structural parameters of discharge capacity of the Piano Key weir was summarized, and the optimal values were suggested. Different overflow patterns formed on the Piano Key weir under different hydraulic conditions. Low water head behavior happened when the water head flowing on the Piano Key weir was low. Based on the existing experimental data, the hydraulic condition and structural parameters when low water head behavior happened were statistically analyzed. A comparative analysis on the existing discharge capacity estimation formulas of the Piano Key weir was performed. Then, based on the existing experimental data, a new discharge coefficient formula including L, W, B, P, W_i/W_o and B_o/B_i was proposed using the least squares method and genetic algorithm, and the predicted results were in good agreement with the experimental data of a large number of different Piano Key weirs with the average error less than 6%. Among the estimation formulas, Machiels’ formula is suitable for the detailed analysis of the discharge of the Piano Key weir. The new formula in this study and Guo Xinlei’s formula are both simple in calculation and can be used to estimate the overall discharge capacity of the Piano Key weir, and the suitable formula can be selected according to the practical requirement.