Numerical and experimental characterization of the 2D vertical average-velocity plane at the center-profile and qualitative air entrainment inside a gully for drainage and reverse flow

Gullies are devices that connect the surface system to the sewer allowing the drainage of water during a rainfall event. During severe flooding, the sewer might become pressurized and water may gush out of the sewer onto the surface, in what is termed reverse flow. Experimental and numerical studies of gullies are rare because of the high computational time and the experimental facilities costs. In this paper we aim to characterize the average velocity inside a gully at the center profile and discuss the qualitative air-entrainment structure for both drainage and reverse flow conditions. The experimental facility termed the Multiple-Linking-Element experiment (MLE) is located at the University of Coimbra. OpenFOAM™ v.1.7.1 is used with the Large Eddy Simulation (LES) Smagorinsky model to simulate turbulence. Numerical and experimental results show reverse flow with a strong jet at the center and an anticlockwise vortex on the left side of the gully box, and drainage flow with a large clockwise vortex located above and slightly to the left of the bottom outlet. Reverse flow shows few traces of air-entrainment, unlike drainage flow that exhibits large quantities of air-entrainment caused by a hydraulic jump formed on the surface flow.