Maximum transient pressures in a rapidly filling pipeline with entrapped air using a CFD model

The aim of this research is to assess the maximum transient pressures in a rapidly filling water pipeline containing entrapped air. A three-dimensional computational fluid dynamics model is used to simulate the rapid filling process and to describe the maximum transient pressures for a given range of initial conditions (i.e. air pocket size and initial pressure differences). Results are compared with experimental data. The air pocket size that leads to the highest maximum pressure (critical air pocket size) has been obtained for each initial pressure difference. Two types of behaviours have been identified at the maximum compression of the air pocket: air compression preserving a clear air-water interface and total air compression with the collapse of the air-water interface. The former typically occurs for small air pockets combined with low initial pressure differences, whereas the latter occurs for large air pocket sizes with high initial pressure differences.