Effects of valve opening on direct water hammer pressure characteristics in PMMA pipelines

In recent years, the application of viscoelastic pipelines in water supply engineering has become increasingly common. In pipes with viscoelasticity, the viscoelasticity of the pipe wall will attenuate the pressure wave as it propagates. Elastic materials have a different relationship between stress and strain than elastic materials. Whether the direct water hammer is generated by rapidly closing the valve under different valve initial opening degree from the transient elastic flow theory needs to be investigated in depth, as the deformation comprises instantaneous and delayed deformation components. A series of experiments is conducted in this paper to study the direct water hammer pressure generated in the polymethyl methacrylate (PMMA) pipeline when the valve initial opening degree is 100 and 30% at different flow velocities and obtains the effect of valve initial opening degree on the change in the direct water hammer pressure in the viscoelastic pipeline. The three-dimensional numerical simulation of the flow field near the valve was performed by using ANSYS-FLUENT. The results show that the value of the direct pressure of the water hammer in PMMA pipes is larger than that in Joukowsky formula, and all exceed the theoretical pressure value at the first wave peak. The variation in the valve closing time and the initial opening degree has an effect on the magnitude of the direct water hammer pressure in PMMA pipelines. Under the condition of 6 different flow rates with the same valve closure time, the direct pressure of the water hammer generated by 30% valve initial opening is larger than that generated by 100% valve initial opening with fast valve closure, and the pressure difference is between 5.62 and 10.48%. The obtained results via numerical simulation show the turbulent flow pattern near the valve and the large average flow velocity under a small valve opening degree. This phenomenon leads to the generation of a large direct water hammer pressure via the sudden closing of the valve.

Automated summary

In recent years, the application of viscoelastic pipelines in water supply engineering has become increasingly common. The viscoelasticity of the pipe wall in these pipelines attenuates the pressure wave as it propagates. The relationship between stress and strain in viscoelastic materials differs from that of elastic materials. This study investigates the generation of direct water hammer from rapidly closing valves with different initial opening degrees using transient elastic flow theory, taking into account both instantaneous and delayed deformation components. Experimental and numerical simulation results demonstrate the effect of valve initial opening degree on the direct water hammer pressure in viscoelastic pipelines.