Effect of Pipe-End Material on Water Hammer and Cavitation in Viscoelastic Pipelines

Abstract

Water hammer in viscoelastic pipelines can be accurately predicted by the classical model. However, discrepancies are observed in case of cavitation, even by use of the classical viscoelastic discrete gas cavity model (VE-DGCM). This paper deals with the improvement of the numerical solution of water hammer and cavitation in viscoelastic pipelines by involving the pipe-end rigidity in boundary conditions. The method of characteristics (MOC) is used to calculate fluid transient in both downstream and upstream-valve HDPE straight pipe, which are rigidly anchored. The classical viscoelastic modelling is used for both cavitating and non-cavitating flows. Pressure as well as circumferential strain are calculated at the valve and at the midstream of the pipe. Two types of pipe-end material are compared therein: the rigid end and the viscoelastic end. The former is considered as the rigid material of the pipe and the reservoir, while the latter is restricted to the pipe. The method consists in incorporating the end behavior in the boundary conditions of the problem. The classical viscoelastic discrete vapour cavity model (VE-DVCM) and the VE-DGCM are used to solve the problem. The calculation shows that the first assumption leads to more accurate results than the second in the two pipe locations.