A study of the numerical simulation of water hammer with column separation and cavity collapse in pipelines

Enbin Liu,Dandan Wen,Haiyang Sun,Shanbi Peng,Yi Yang

doi:10.1177/1687814017718124

Abstract

The numbers of long-distance transport pipelines constructed in areas with relatively complex terrain and large topographic changes have increased in recent years. A water hammer can occur easily during operational processes, such as the starting and stopping of a pump station, the adjustment of the speed of a pump unit, and a shutdown due to an incident and failure of a regulating valve. These operations may cause fluid column separation and form a dangerous water hammer due to the collapse of air cavities. Water hammers due to the collapse of air cavities are a complicated two-phase (gas–liquid) fluid mechanics problem. This study carries out a theoretical study and a numerical simulation of water hammers that occur due to the collapse of flow interruption–caused air cavities and their prevention. This study establishes and solves a discrete model for air cavities caused by flow interruptions and develops a program to numerically simulate water hammers that occur due to the collapse of these air cavities. In addition, based on an actual pipeline incident in which the stopping of a pump resulted in water hammers at multiple locations due to the collapse of air cavities from fluid column separation, numerical simulations are used to plot the lowest and highest hydraulic head envelope curves and the transient curves of the water hammer at the major points, analyze the transient process of the pipeline system, and propose a preventive measure that can effectively control the water hammer pressure and reduce the occurrence of incidents.

Highlights

IntroductionNumerous researchers have performed extensive studies on the two-phase (gas–liquid) transient process that results from water hammers due to the collapse of flow interruption–caused air cavities and have examined the effect of gas release on the transient process of liquid column separation.[1]
Numerous researchers have performed extensive studies on the two-phase transient process that results from water hammers due to the collapse of flow interruption–caused air cavities and have examined the effect of gas release on the transient process of liquid column separation.[1]By calculating and measuring water hammer data from two water transport pipelines, Brown found that the dissolved gas in the water should not be neglected during the analysis of water hammers and showed that the higher the gas content, the higher the reverse rotation speed of the pump and the water hammer surge head during the water hammer process.[2]
Most of the lowest hydraulic head envelope curve will not be lower than the elevation of the pipeline axis

Summary

Introduction

Numerous researchers have performed extensive studies on the two-phase (gas–liquid) transient process that results from water hammers due to the collapse of flow interruption–caused air cavities and have examined the effect of gas release on the transient process of liquid column separation.[1]. When the pressure at a location in a pipeline decreases to below atmospheric pressure and liquid column separation begins to occur due to the effect of a water hammer wave, air is automatically injected via the air valves until the flow rates of the liquid columns on both sides of the air cavity are the same. At this time, the cavity is completely filled with air, and the pressure in the cavity is equal to atmospheric pressure. The total duration of valve closure (TC) is 20 s

Valve at the end of the pipeline

Results and discussions

Conclusion