Investigations of column separation influence on pressure waves severity based on results of water hammer experiments in elastically supported pipeline

Abstract

Water hammer (WH) events are involved in pipelines when the flow is disturbed by any reason changing its velocity, which produces pressure variations and elastic waves propagating in liquid along a pipeline at the acoustic wave-speed. These phenomena stay more complex if dynamic fluid-structure interaction takes place. More dangerous scenarios may happen in the case of liquid cavitation, which appears when the instantaneous local pressure drops down to the level of the liquid vapor pressure. Bubbles of vapor are created, which can be distributed in specific areas of pipes (distributed cavitation) or may form one larger vapor space between two parts of water column (column separation = CS). In the paper analyses of CS effects are presented based upon experiments performed in the laboratory of the Institute of Fluid-Flow Machinery. Water hammer runs in a copper pipeline fixed to the foundation with elastic supports were generated while pressure oscillations and pipeline vibrations were being measured. For certain initial and boundary conditions CS effects were observed. Analyses of these events were performed for varying initial conditions and support stiffness. The general conclusion is that, more elastic pipeline fixing allows to reduce CS behaviors, more effectively. Further discussion and conclusions are also presented, specifically on WH energy dissipation effects.