琴键堰泄流能力特性分析

Discharge capacity characteristics of Piano Key Weir

琴键堰（P.K堰）是目前水库大坝溢洪道升级改造新技术中出现的堰型，它能有效解决现有水库极端致灾因子条件下泄流能力急剧增加的问题。设计P.K堰首先要研究其泄流能力特性，它直接关系到PMF条件下最大水库水位或库容的确定。本文首先对最近两年发表的P.K堰泄流能力公式进行了对比，然后结合已有试验数据，通过量纲分析和多参数优化，给出了推荐公式，并利用该公式对P.K堰的泄流特性和超泄能力进行了研究。结果表明，当上游水头较小，一般H/P〈;0.2时，P.K堰流量系数较大，超泄比系数大于3，泄流量增量比较明显，随着上游水头的增大，堰的总宽度对泄量起主要作用，其泄量增大的优势也越来越弱，实用范围内的超泄比在1.2-3.5之间。本文给出公式的预测值跟已发表的试验值符合良好，平均误差在5%-8%，比Machiels公式误差更小，该公式可供P.K堰泄流能力评估和优化设计时参考。

The concept of Piano Key Weir （PKW） is a new technique and trend used to rehabilitate numerous existing dams, which can increase the unit discharge at the unregulated spillway inlet for similar heads and widths. As it is a relatively novel structure, its hydraulic design remains problematic. The discharge capacity character is one of the most important hydraulic features which directly linked to the maximum reservoir level during floods under PMF. The recently published equations relating to the head discharge ratio of PKW was summarized. Combining with the existing experimental data, the paper proposed a new formula based on the dimensional analysis and multi-parameter optimization,then the discharge capacity and increase ratio of PKW was studied. The results show that the efficiency of PKW is particularly high for the small head ratio of H/P, for H/P〈0.2, the increase ratio is bigger than 3 and then the total length plays the leading role when H/P increased. The practical extend of increase ratio is between 1.2 and 3.5. Also the predicted values agree well with the published experimental results with the average error less than 8%, which is smaller than the Machiels equation. The proposed head discharge relationship can be used for the design of PKW and helps to provide a reference.