Modeling Interactions between Hydraulic Transients and Inline Air Pockets in Water Pipelines: Dynamic Behavior and Energy Dissipation

The existing one-dimensional model is inadequate in predicting the dynamic interactions between hydraulic transients and inline air pockets in water pipelines, leading to underestimated pressure dissipation in the modeling results. In this study, a one-dimensional (1D)-three-dimensional (3D) coupling model was applied to analyze and explain the interactions between the hydraulic transients and inline air pockets observed in systematic laboratory experiments. In this model, the method of characteristics provides 1D modeling of hydraulic transients in the regions without the inline air pocket and the finite-volume method with volume of fluid approach provides 3D modeling of hydraulic transient interactions at the air pocket. The coupling between 1D and 3D models is achieved using the partly overlapped coupling method. The analysis of the transient velocity profile unveils unique velocity distributions on both sides of the air pocket due to reflection and transmission processes, which contribute to the compression and movement of the air pocket. The investigations of variation in the internal energy of the air pocket using the 1D-3D model demonstrate that the internal energy reduces in the slow compression process due to greater energy fluctuations and more rapid energy transfer between air and water, especially at the front of the air-water interface directly impacted by the incident wave. This explains why the existing 1D model underestimates the pressure damping.