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

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.