基于管嘴出流规律的水击边界条件数值模拟

为研究阀门关闭瞬间产生的水击压力,以管嘴出流规律来确定阀门断面的水头和流量的关系,并结合特征线方程,以水击实验台为模型,用MATLAB编程进行水击模拟计算.结果表明:阀端压力随阀门关闭先迅速上升,0.36 s达到最大值,之后压力又迅速下降;随着时间的增加,阀端压力不断重复上升到峰值然后又下降,但其最大压力都小于第1个峰值.将其与水击实验台的试验结果对比分析,验证了管嘴出流模型以及计算程序的准确性.故在简单的有压管道中,当管道末端为阀门时,可以按照管嘴出流规律来建立边界条件.在此基础上依次取阀门关闭时间为1.0,2.0,3.0,4.0,4.8 s,模拟了阀门关闭时间对最大水击压力的影响.结果显示,阀门关闭时间对水击压力有很大影响:关阀时间越长,产生的最大水击压力越小,但随着阀门关闭时间的延长,水击压力的减小幅度会越来越小.

Numerical simulation of water hammer boundary conditions based on nozzle outflow law

In order to study the water hammer pressure generated at the moment of valve closing, the relationship between the head and flow of the valve cross section was determined by the nozzle outlet flow rule; combined with the characteristic line equation, the water hammer test bench was used as a model, and MATLAB was used to perform water hammer simulation calculations. The results show that the valve end pressure rises rapidly with the valve closing, reaches a maximum value of 0.36 s, and then drops rapidly. With the increase of time, the valve end pressure continuously rises to a peak and then decreases, but its maximum pressur is less than the first peak. By comparing and analyzing with the experimental results of the water hammer test bench, the accuracy of the nozzle outflow model and the calculation program are verified. Therefore, in a simple pressure pipeline, when the end of the pipeline is a valve, the boundary conditions can be established according to the nozzle outlet flow law. On this basis, the valve closing time is taken as 1.0, 2.0, 3.0, 4.0, and 4.8 s in order, and the effect of the valve closing time on the maximum water hammer pressure is simulated. The results show that the valve closing time has a great effect on the water hammer pressure. The longer the valve closing time, the smaller the maximum water hammer pressure. However, as the valve closing time increases, the decrease of the water hammer pressure will become more and more small.