大型倒虹吸工程水头损失及水力计算

针对三个泉倒虹吸实际过流能力富余、小洼槽倒虹吸实际过流能力不足的问题,基于工程特点及水力设计习惯,借鉴当量糙度的取值方法,分析了不同流量下三个泉与小洼槽倒虹吸的沿程水头损失,并与实测值对比。结果表明:对于三个泉倒虹吸的PCCP管和钢管,用柯尔布鲁克公式计算所得的水头损失与实测值更接近,明显小于水力设计时采用谢才公式所得值;对于小洼槽倒虹吸的玻璃钢管,用柯尔布鲁克公式计算所得的水头损失与实测值也更接近,但明显大于水力设计时采用谢才公式所得值。在此基础上,利用计算获得的沿程水头损失反算得出糙率n值和当量糙度Δ值,发现实际过流能力出现偏差的主要原因是水力设计时采用的谢才公式不适用于大口径倒虹吸管道内的流态。

Water head loss and hydraulic calculation of large inverted siphon project

In view of the problem that the actual flow capacity of the Sangequan inverted siphon is surplus while the Xiaowacao invert siphon is small, based on the engineering characteristics and the hydraulic design habit, frictional head losses of the Sangequan and Xiaowacao inverted siphons under different flows are analyzed and compared with the measured values. The results show that the head loss calculated by the Colebrook formula is closer to the measured value for the PCCP pipe and the steel pipe in the Sangequan inverted siphon, which is obviously less than the hydraulically designed value using the Chezy formula. For the Xiaowacao inverted siphon FRP pipe, the head loss calculated by Colebrook formula is closer to the measured value, which is significantly higher than the hydraulically designed value using the Chezy formula. On this basis, the roughness value and the equivalent roughness value are inversely calculated by the calculated frictional head loss. It is found that the deviation cause of flow capacity calculation is that the Chezy formula is not suitable for the flow pattern in large diameter inverted siphon pipelines.