Evaluation of plane wave assumption in transient laminar pipe flow modeling and utilization

Abstract

The plane wave assumption is key to the formulation of one dimensional (1D) and quasi-2D water hammer models, which have been widely used in the design and evaluation of fluid piping systems. As transient analysis and utilization are becoming more and more popular and important to pipe system diagnosis such as pipe faults (leakage and blockage) detection, a better understanding of the influence of plane wave assumption on the transient responses is necessary and critical to the development and application of such innovative technologies. This study aims to (i) address the efficiency problem of existing 2D scheme, and then extend the full-2D water hammer model to a classical reservoir-pipe-valve system so as to simulate the whole process of typical water hammer event; and (ii) estimate the accuracy of plane wave assumption for reproducing pressure histories under both low frequency wave (LFW) and high frequency wave (HFW) conditions. The results confirm that the plane wave assumption is invalid during the period shortly after valve closure, and the influence of radial pressure wave is evident when the incident wave frequency is larger than the radial wave frequency. Moreover, the radial wave dissipation and dispersion rates are highly dependent on the incident wave frequency. This result may provide implication to the utilization of different transient waves (LFW & HFW) for the pipeline assessment in this field.