Hydraulic Transients in Viscoelastic Branched Pipelines

Abstract

Plastic pipes are widely used in pressurized water systems. Their viscoelastic behavior has to be taken into account in the design phase as well as in the interpretation of water-hammer signals for diagnostic purposes. The aim of the present paper is to experimentally investigate the transient waves’ transmission and reflection in branched networks of high density polyethylene (HDPE) pipes and to test the efficacy of a viscoelastic model for the interpretation of the results. Two laboratory Y-shaped systems were built in the Water Engineering Lab of the University of Cassino and Southern Lazio (Italy) and a set of water-hammer tests was conducted on them. A significant variation of transmission and reflection coefficients at the pipe junction is observed in comparison with the values suggested in classical textbooks. The strong agreement between the experimental pressure values and those obtained using the viscoelastic model suggests that the differences from the classical theory are due to the viscoelastic behavior of the material, since unsteady friction effects are negligible in the investigated scenarios.