Experimental study on pressure characteristics of direct water hammer in the viscoelastic pipeline

With the increasing popularity of long-distance water supply projects and the development of materials technology, the variation of water hammer characteristics in the viscoelastic pipeline has become the focus of researchers. To find out the mechanism of water hammer in the viscoelastic pipe of both elastic and viscous properties, an experiment was set up to study the direct water hammer generated by rapid closure of the downstream valve in the polymethyl methacrylate (PMMA) pipe, with six flow velocities in nearly 70 tests. The experimental results showed that the maximum water hammer pressure generated in the viscoelastic pipe in all flow velocities was (20% at most) greater than the traditional value of Joukowsky's formula. A faster closing time of the valve caused a higher water hammer pressure. The difference in water hammer pressure generated between the fastest and the slowest closing time of the valve was 14–17% at each flow velocity. Based on the relationship between the stress and strain of the pipe wall in the viscoelastic pipe, the reason that the water hammer characteristic in the viscoelastic pipeline was different from the traditional value was explained. The study provides a reference for the mechanism of transient flow in viscoelastic pipelines.