Transients in a series of two polymeric pipes of different materials

The effects of the variation of the viscoelastic pipe material properties on the transient pressure wave propagation are investigated through laboratory and numerical tests. The used experimental set-up consists of a series of a high-density polyethylene (HDPE) pipe with an oriented polyvinyl chloride (PVC-O) pipe. A pulse and a step pressure wave are introduced in the system using an automatically controlled butterfly valve. A numerical model calibrated on the experimental results is used to investigate the effects of each parameter of a standard linear viscoelastic model on the pressure wave reflection. Results show that the reflection coefficient at the junction between the two pipes depends on all the viscoelastic parameters and on the transient time-history. The analysis of the negative pulse wave propagation reveals a pressure head increase in the pipe due to the retarded strains, which cannot be explained by an elastic model.