Investigation of Hydraulic Transients in a Pipeline with Column Separation

The authors previously described a new method [based on the new discrete vapor cavity model (new DVCM)] for numerical prediction of pressure changes during the water hammer with liquid column separation together with results of preliminary experimental verification of this method. This paper is a continuation of the research and includes results of additional laboratory tests and visualization of the cavitation zones generated during transient flow with liquid column separation. The results of these studies provide a better understanding of the phenomenon. It is shown that the phenomenon can have a distributed nature, which means that gas-vapor zones may be observed not only locally, in the vicinity of the shutoff valve, but may be spread along the pipeline length, and the intensity of this phenomenon decreases with distance from the valve. Laboratory test results were also used for further verification of the new DVCM. This verification shows that agreement between calculated and experimental results strongly depends on the friction model incorporated into the calculation. This agreement also depends on the intensity of liquid column separation: for cases of severe separation, the differences between numerical and measured pressure changes are small and accepted from the practical point of view.

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