Critical Submergence for Lateral Rectangular Intakes: A CFD Study

The formation of an air-entraining vortex in the vicinity of an intake is considered a severe problem for intakes. An intake is a short or long pipe with more than three times its diameter connected to the face of an orifice, which is provided in the side or bottom of a vessel or channel. The depth of water at which the tail of a free surface vortex core just reaches the tip of an intake, causing air entrainment, is referred to as critical submergence for that intake. Few studies have been reported in the literature on rectangular intakes for the computation of critical submergence compared to circular or square intake configurations. The present study discusses the numerical investigation of critical submergence for rectangular intakes placed laterally on the side wall of an open channel under uniform flow conditions. A series of numerical simulations were performed to compute the critical submergence for rectangular intakes. A three-dimensional multiphase CFD model was developed to simulate critical submergence at intakes. Reynolds-averaged Navier–Stokes (RANS) equation with SST k-ω turbulence model was used to simulate the fluid flow inside the computational domain. These models, together with the volume of fluid (VOF) two-phase (water-air) model, were found well capable to simulate the flow at critical submergence. Surface streamlines and phase volume fraction analysis studies were used to identify the air-entraining vortex at critical conditions. Multiphase CFD study assisted in understanding the flow structure and turbulence characteristics of the vortex flow at the vicinity of intakes. The approach Froude number and intake Froude number play a vital role in computing critical submergence with CFD simulations.