Numerical simulation of transient pipe flow with entrapped air and wet bed effects

In this study, the evolution of transient pipe flow along the wet bed is numerically investigated. In the investigation, the shear stress transport k-omega model is used and the volume of fluid method is employed to track the surface of air and water. Two key parameters in the flow as upstream head H and initial water depth h in the pipe are examined. It is found that the bottom stress is significantly affected by the two parameters. The upstream head H determines the magnitude of the shear force, and the downstream water depth in the pipe affects the stability of the shear force. The boundary layer separation and flow pattern are the essential causes of shear instability. By analyzing the simulation results, an empirical equation with the average flow velocity is obtained to estimate the overflow capacity of the pipe by just the upstream water level and the depth of the wet bed. (c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This study numerically investigates the evolution of transient pipe flow along the wet bed. The shear stress transport k-omega model and volume of fluid method are applied for simulation. Two key parameters, upstream head H and initial water depth h in the pipe, are examined and found to significantly affect the bottom stress. The analysis reveals that boundary layer separation and flow pattern lead to shear instability, and an empirical equation with average flow velocity is derived to estimate the overflow capacity of the pipe using just the upstream water level and wet bed depth.