泄洪洞渥奇系数选择的简捷方法

目前已建泄洪洞常利用施工期导流洞,洞线形式常采用龙抬头式,其洞身渐变段常采用抛物曲线以平顺水流。渥奇系数根据经验、工程重要程度、投资选定,具有较大的不确定性,选择不合理容易引起水流脱体导致建筑物空蚀等不良水力现象,严重时甚至危及工程安全。为找到一种简捷、合理确定渥奇系数的方法,以石头峡水电站泄洪洞为例,利用模型试验与数值计算方法对不同渥奇曲线体型壁面压力分布进行了研究,得到临界渥奇系数与流能比的关系。对若干已建泄洪洞工程进行渥奇系数的分区研究,结合模型试验及数值计算成果,分析拟合得到了可用于渥奇系数选择的经验公式A=467-934q/(g~(0.5)·H~(1.5))。与实际工程采用的渥奇系数相比结果表明,该公式形式简单,具有较高的准确度,可为以后相关工程设计提供参考。

A simple method for selection of ogee coefficient of spillway tunnel

At present, the existing spillway tunnels are frequently constructed by utilizing the construction diversion tunnel, for which ogee type is often adopted for the tunnel route with the transition section in form of a parabolic curve for smoothening water flow. The ogee coefficient is selected according to the relevant experiences, importance degree and investment, and then has a larger uncertainty, thus the unreasonable selection of it is prone to lead to flow separation, and then causes the undesirable hydraulic phenomena, such as cavitation of structure, etc. and even endanger the safety of the project when it is serious. In order to find out a method to simply and reasonably determining the ogee coefficient, the distributions of the wall pressures for different types of ogee curve are studied with the relevant model experiments and numerical calculation methods by taking the spillway tunnel of Shitouxia Hydropower Station as an actual case, the relationship between the critical ogee coefficient and the flow-energy ratio is obtained. Afterwards, the zoned studies are made on the ogee coefficients for several existing spillway tunnels and then the empirical formula, i. e. A = 467-934 q/ ( g (0. 5) ·H (1. 5) ) , that id suitable for selecting the ogee coefficient is obtained through the relevant analysis and fitting. Compared with the ogee coefficient adopted for the actual project concerned, the formula is simple with a higher accuracy, which can provide a reference for the relevant project in the days to come.