Overpressurization can cause safety problems when pipes containing entrapped air undergo rapid filling conditions. One-dimensional mathematical models have been developed in order to predict peak pressures, which are based upon the equations of continuity, momentum and thermodynamics of air. A common hypothesis has been adopted in these models, as there exists a distinct vertical air-water interface throughout the filling process. The limitation on the assumption becomes significant for cases with large diameter, where the filling front undergoes notable deformation due to density difference and gravity effects. Interface breaking and air-water mixing also cannot be reproduced in those simplified models. This study modeled air-water interactions in a horizontal pipe over rapidly filling processes, by using the compressibleInterFoam solver of OpenFOAM. Both empty and partially-filled pipe filling cases were simulated and compared with rigid-column models. Comprehensive analyses are presented, including detailed velocity profile, pressure distribution, temperature variation of entrapped air and interface evolution. The results indicate that the transient water flow is analogous to waterhammer flow and that the contribution of air-water mixing on the pressure damping is considerable. The findings are helpful to better understand the physics of such flow and to improve numerical models.

Access the Conference Proceedings Paper on ASCE Library

Overpressurization can cause safety problems when pipes containing entrapped air undergo rapid filling conditions. One-dimensional mathematical models have been developed in order to predict peak pressures, which are based upon the equations of continuity, momentum and thermodynamics of air. A common hypothesis has been adopted in these models, as there exists a distinct vertical air-water interface throughout the filling process. The limitation on the assumption becomes significant for cases with large diameter, where the filling front undergoes notable deformation due to density difference and gravity effects. Interface breaking and air-water mixing also cannot be reproduced in those simplified models. This study modeled air-water interactions in a horizontal pipe over rapidly filling processes, by using the compressibleInterFoam solver of OpenFOAM. Both empty and partially-filled pipe filling cases were simulated and compared with rigid-column models. Comprehensive analyses are presented, including detailed velocity profile, pressure distribution, temperature variation of entrapped air and interface evolution. The results indicate that the transient water flow is analogous to waterhammer flow and that the contribution of air-water mixing on the pressure damping is considerable. The findings are helpful to better understand the physics of such flow and to improve numerical models.

**[Access the Conference Proceedings Paper on ASCE Library](https://doi.org/10.1061/9780784483466.045)**

CFD Simulation of Air-Water Interactions in Rapidly Filling Horizontal Pipe with Entrapped Air

Created in 1999, the Environmental & Water Resources Institute (EWRI) is the recognized leader within ASCE for the integration of technical expertise and public policy in the planning, design, construction, and operation of environmentally sound and sustainable infrastructure impacting air, land and water resources.

[Paper Proceedings](https://doi.org/10.1061/9780784483466)

Conference DOI: https://doi.org/10.26226/m.6329c39b68fb0e00131f77d2