Experimental and Numerical Modeling of Critical submergence for Water Intakes

A series of experimental and numerical studies were performed to investigate Critical submergence for square water intakes in an open channel flow in this paper. Diversion of water from rivers has recently become a most important subject of study in hydraulic projects, such as water supply, irrigation, power plants, etc. The formation of an air-entraining vortex in the vicinity of an intake is considered to be a severe problem for water intake. The distance between the water surface level and the intake center level is called the submergence of a water intake. Suppose submergence is below a definite lowest level. In that case, air enters into the intake through an air-entraining vortex developing from the free surface, and that specific submergence is termed as critical submergence. Experiments were performed in a concrete flume of 9.47 m long, 0.5 m wide, and 0.6 m deep with an intake of size 0.04 m×0.04 m under uniform approach flow for different flow conditions. A three-dimensional Multiphase CFD Model was also developed for simulating critical submergence for the intakes. Reynolds-averaged Navier–Stokes (RANS) equation with Standard k-ω and SST k-ω turbulence models were used to simulate the fluid flow inside the test domain. These two models, together with the volume of fluid (VOF) two-phase (water-air) model, were found well capable to simulate the flow at critical submergence. Air entraining vortex at critical conditions was identified using phase volume fraction studies and surface streamlines. Multiphase CFD study helped to understand the flow structure and turbulence characteristics of the vortex flow at the vicinity of intakes. The interface between air-water phases has been simulated with better accuracy for identifying the multiphase interface interaction during the event of an air-entraining surface vortex formation. It should be noted that approach flow Froude number and intake flow Froude number play a vital role in observing critical submergence with both experimental and numerical considerations. A comparison of the numerical and experimental results with the selected turbulent model indicated that the multiphase numerical model is capable for simulating flow for air-entraining vortex formation at critical submergence with an 8 % error.