Author(s): Xiangpeng Mu; Zihou Niu; Wenxue Chen; Wei Cui; Zheqi Zhang
Linked Author(s): Wei Cui, Xiangpeng Mu, Wenxue Chen
Keywords: CFD VOF CLSVOF CFD-PBM Air pocket
Abstract: Long-distance pressurized water supply systems often need to traverse complex topographical and geological conditions, leading to uneven pipeline elevation. If air release valves are improperly installed or if air is not vented in a timely manner, air pockets may become trapped during the water filling process, adversely affecting pipeline safety and water transport efficiency. Accurately simulating the interaction between water and air has long been a challenge in long-distance water conveyance projects. This study employs three models -- Volume of Fluid (VOF), a coupled level-set and volume of fluid (CLSVOF), and a combination of computational fluid dynamics and the population balance model (CFD-PBM) -- to simulate and compare transient flow cases involving air pockets trapped at the blind end of a pipeline due to water impact. The results indicate that while the three models yield similar calculations for pressure extremes in pressurized pipelines, the CLSVOF model demonstrates superior performance in simulating the fragmentation and coalescence of air pockets, making it more suitable for studying trapped air in long-distance water supply projects. Building on this, the CLSVOF model was used to simulate the migration of trapped air pockets in horizontal tunnels. Under the influence of water flow drag, the air pockets behave like slug flow and can slowly be discharged from the end of the tunnel into a reservoir. The findings provide valuable insights into the migration characteristics of trapped air in long-distance tunnels and related venting issues.
Year: 2025