Numerical model for calculation of hydraulic transients with two-phase flow and fluid-structure interaction

Fluid transport systems such as pipelines are subject to loads whenever changes in fluid momentum or in pipeline structure occur. These loads can generate extremely harmful hydraulic transients which may be responsible for several major accidents. This paper presents a model for the solution of these hydraulic transients, considering two-phase flow and fluid-structure interaction. Mathematical and numerical solutions are proposed and analyzed for the proper capture of the physical phenomena associated with the fluid compressibility and fluid celerity, which are variable in two-phase fluid, together with the disturbances generated by the fluid-structure interaction. The proposed solution for the model considers the simultaneous action of these phenomena. The developed numerical model is based on the solution of the mathematical model formed by a system of four partial differential equations, in which the necessary adaptations are integrated in fluid-structural equations and in the nonlinear mathematical coefficients for the solution of the compressible and two-phase flow in question. Classical formulation is selected for the implementation of friction between fluid and pipe in the model. For the solution, it is applied the method of characteristics and finite difference, with subsequent numerical integration. The validation of the results is carried out based on comparisons with experimental and analytical data. The model presented, in general, was quite adherent to the experimental and analytical results, mainly in relation to the first pressure peak, which is one of the main focuses of the transient analyses.