A Comparison of Different Methods for Modelling Water Hammer Valve Closure with CFD

Abstract

Water hammer is a transient phenomenon that occurs when a flowing fluid is rapidly decelerated, which can be harmful and damaging to a piping system. Three-dimensional computational fluid dynamics (CFD) with three-dimensional geometry is a common tool for studying water hammer, which is more accurate than numerical simulation with one-dimension approximation of the geometry. There are different methods with different accuracy and computational costs for valve closure modelling. This paper presents the result of water hammer 3D simulation with three main technics for modelling an axial valve closure: dynamic mesh, sliding mesh, and immersed solid methods. The variation of the differential pressure variation and the wall shear stress are compared with experimental results. Additionally, the 3D effects of the flow after the valve closure and the computational cost are addressed. The sliding mesh method presents the most physical results compared to the other two methods. The immersed solid method predicts a smaller pressure rise which may be the result of using a source term in the momentum equation instead of modelling the valve movement. The dynamic mesh method adds fluctuations to the primary phenomenon. Moreover, the sliding mesh is less expensive than the dynamic mesh method in terms of computational cost (approximately one-third), which was the primary method for axial valve closure modelling in the literature.