Numerical Simulation of Transient Flow in Pressurized Water Pipeline with Trapped Air Mass

The 2D VOF (volume of fluid) model is introduced in this paper to simulate the rapid filling process in pressurized water conveyance pipeline with trapped air mass. The movement of gas-water interface, the pressure distribution, the maximum pressure and the position of its occurrence during the filling process are modeled and analyzed. According to the results, the sudden pressure increase caused by the water striking on pipe wall could happen, and is sensitively influenced by the geometry parameters of pipeline. When the occurrence time of water striking on pipe wall is prior or close to that of the maximum air pressure, the maximum pressure of the system is obviously greater than the maximum air pressure numerically. With the increase of the diameter of pipeline, the maximum pressure of the system increases gradually, and the phenomenon becomes clearer when inlet pressure is higher. Obviously, the above-drawn conclusions are essentially different from those based on one- dimensional model, such as "the maximum air pressure is the maximum pressure of the system" and "the maximum system pressure changes with the diameter of pipeline but slightly", which are caused by the inherent limitations of the simplification and the basic assumptions of one-dimensional model.