Fluid-Structure Interaction During Viscoelastic Fluid Hammer Phenomenon in the Pipes

Viscoelastic fluid hammer is a type of fluid hammer in which a viscoelastic non-Newtonian fluid flows in a pipeline. In this study, the fluid-structure interaction in this phenomenon is investigated. The governing equations are viscoelastic fluid and structure equations which are coupled together. Viscoelastic fluid equations consist of continuity and momentum which govern the transitional flow in the pipes. Oldroyd-B model is used as the constitutive equation. This model is suitable for dilute viscoelastic solutions and Boger liquids. Structural equations include pipe axial velocity and stress equations. A two-step variant of the Lax-Friedrichs method is used to simulate fluid-structure interaction in a reservoir-pipe-valve system. A viscoelastic fluid polymer is selected and the behavior of the polymer pressure head and shear stresses during fluid hammer is investigated. Three types of couplings were examined. Junction, Poisson, and the combination of two aforementioned couplings called junction and Poisson coupling. The effects of these couplings for the fluid are modeled in three states. ideally, Newtonian and viscoelastic. The fluid viscosity in Newtonian and viscoelastic states is considered the same. The results of the study show that the imposed shear stresses with viscoelastic fluid are significantly lower than those in the Newtonian state. Comparing coupling effects during fluid hammer is found that the lowest shear stresses are assigned to Poisson coupling.