Investigation of parameters affecting discrete Vapour cavity model

Rapid valve closure or pump shutdown causes a fast transient flow with column separation which causes problems such as hydraulic equipment damage and cavitation. This paper presents a numerical study of water hammer with column separation in a simple reservoir-pipeline-valve system. The governing equations for two-phase transient flow in pipes have been solved based on the method of characteristics using a discrete vapour cavity model (DVCM) which has been coupled with four different friction models including the Brunone, Zielke, Vardy and Brown, and quasi-steady friction. The DVCM may produce unrealistic pressure pulses (spikes) due to the collapse of multi-cavities. Studies of the DVCM have suggested that using a weighting factor close to 1.0, using unsteady friction term in the DVCM and restricting the number of reaches improve the computational results and the present paper explores this suggestion in detail. The simulation results clearly show that using unsteady friction term in the DVCM reduces the unrealistic pressure pulses. It has been observed that using a weighting factor close to 1.0 and restricting the number of reaches do not improve the computational results in all cases. Instead, proper selection of these parameters reduces the unrealistic pressure pulses.

Keywords:

Column separation , Discrete vapour cavity model , Pipelines , Quasi-steady friction model , Unsteady friction model , Water hammer