Author(s): Bhagwan Das; Zulfequar Ahamad; Pramod Kumar Sharma

Linked Author(s):

Keywords: Critical submergence; Hydraulic intakes; Open channel flow; Multiphase flow

Abstract: In this study, critical submergence for square water intakes in an open channel flow is investigated through experimental and numerical analyses. In the recent years, there have seen a significant increase in the importance of water diversion for water supply, irrigation, power plants, etc. It is considered a serious issue for water intake when an air-entraining vortex forms at an intake. The submergence of a water intake is the distance between the water surface level and the intake centre level. If submergence is below a certain minimum level, 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 conducted 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. The fluid flow inside the test domain was simulated using the Reynolds-averaged Navier-Stokes (RANS) equation along with the Standard k-ω and SST k-ω turbulence models. These two models, along with the volume of fluid (VOF) two-phase (water-air) model, were shown to be very effective in simulating the flow at critical submergence. Surface streamlines and phase volume fraction investigations were used to locate air entraining vortices under specific conditions. Multiphase CFD study assisted 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 was found that approach flow Froude number and intake flow Froude number play a significant role in formation of air-entraining vortices. A comparison of the numerical and experimental results showed that the multiphase numerical model is capable for simulating flow air-entraining vortex formation at critical submergence. Also, the modelling technique was validated with experimental data with good agreements with an error 8%.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1194-cd

Year: 2023