负压输水光滑管道水力摩擦系数的试验研究

Experimental study on friction factors for water flow in smooth pipe flow under negative pressure

为了研究虹吸进流在某些输水工程改造中取得显著效果的内在机理,通过在实验室内进行复杂起伏管路的局部窝气/没窝气情况下阻力特性试验,并对试验管道(DN50有机玻璃管)的水力摩擦系数进行了试验预估,得到了比基于穆迪图估算更低的数值.为了排除该复杂管路中诸多弯头、球阀等部件对试验结果的干扰,重新搭建了一套前端带有虹吸负压整流装置的简单直管系统,对负压情况下的圆管流动水力摩擦系数进行了试验研究.管道为透明有机玻璃,可视为水力光滑管道.通过测量直管上两相距18.4 m的侧压点,在不同流量下得到其水力摩擦系数,测试不仅获得比先前更低的水力摩擦系数,而且随雷诺数变化表现出一种新的趋势,由此得出负压对管道流动有着重要的影响.

In order to investigate the internal mechanism why the siphon inlet has achieved a significant effect in solving the problems of some water transportation projects,some early pipe resis-tance tests had been performed by considering with and without air-traps on an undulating pipe layout in our laboratory,the friction factor measured from a DN50 pipe made of transparent acrylic tube was found far below the value estimated from Moody Chart.This conclusion was not convincible due to that there were the influence of so many bends and spherical valves in the tested undulating pipe layout,therefore a simple long straight siphon layout with a multi-hole bottom valve at its inlet was constructed in the laboratory,an experimental study on the friction factor of this circular pipe under negative pressure has been studied further.The whole pipeline was made of acrylic tube,so it could be treat as hydraulically smooth pipe.The friction factor had been derived from the measurements of the pressure difference of two taps with an interval of 18.4 m located on its straight section under various discharges,A lower friction factor has been obtained than that from previous researchers,and it shows a different trend against the Reynolds number variation,therefore it is concluded that the negative pressure has an important impact on the pipe flow.