Simulation of flow transients in a water filling pipe containing entrapped air pocket with VOF model

Abstract

The pressure within an entrapped air pocket in a filling pipeline without air release is investigated both experimentally and numerically. Volume of Fluid (VOF) model is introduced to simulate the transient flow. Both VOF model and experimental observations show that the air-water interface moves irregularly, and the water column near bottom pipe wall firstly reaches and impacts on pipe end wall, which could induce a sudden pressure jump. Due to assumptions of "air pocket occupies entire cross section" and "air-water interface is perpendicular to pipe centerlme", the existing one-dimensional model is incapable of calculating the jump pressure. Comparisons between calculated and measured results demonstrate that VOF model is effective to simulate movement of air pocket and pressure surge. In a one-dimensional model, only the first peak pressure is close to the measured value, but the following peak pressures are not. Therefore, VOF model is a feasible and more advanced method to investigate further this problem.