Flow regime transition simulation incorporating entrapped air pocket effects

Abstract

Flow regime transition is observed in closed conduit when there is a transition between free surface and pressurized flows. This condition is often observed in stormwater storage tunnels undergoing rapid filling. Such tunnels provide stormwater control inurbanized areas, relieving the stormwater collection system during intense storms. Operational issues have been reported in such tunnels during intense rain events, some of which linked to air pocket entrapment. These issues motivated development of flowregime transition models and more recent models attempt to improve predictions by accounting for air effects in formulations. However, no comparative study has been performed between recent models that account for air pockets and earlier models that don't include this feature. This work aims to address this gap, focusing on an actual tunnel geometry that was proposed for the city of Washington, DC. Results indicate that including air in model formulation yielded more realistic predictions of low pressures.

Keywords::

• flow regime transition
• stormwater storage tunnels
• air pockets
• numerical modeling