Flow Modeling in Symmetrically Narrowing Flood Plains

Abstract

Flooding situation in river is a complex phenomenon and affects the livelihood and economic condition of the region. The modelling of such flow is primary importance for a river engineers and scientists working in this field. As a result of topography changes along the open channels, designing the converging compound channel is an essential. Fluvial flows are strongly influenced by geometry complexity and large overall uncertainty on every single measurable property, such as velocity distribution on different sectional parameters like width ratio, aspect ratio and hydraulic parameter such as relative depth. The geometry selected for this study is that of a non-prismatic compound channel having converging flood plain. For the research work the parameters, the water depth, incoming discharge of the main channel and floodplains were varied. Continuous variation of channel geometry along the flow path associated with secondary currents makes the depth averaged velocity computation difficult. In this paper the variations of depth average velocities for five different sections in between the convergence region of the converging compound channel are compared by taking two different flow depth conditions. And also shear stress distribution at the walls and on the bed of two stage converging compound channel is calculated by doing experimentation in laboratory as bed shear forces are useful for the study of bed load transfer whereas wall shear forces presents a general view of channel migration pattern. Then the numerical method is applied to analyse the flow conditions in non-prismatic compound channel configurations, the results of calculations show good agreement with the experimental data. As numerical hydraulic models can significantly reduce costs associated with the experimental models, an effort has been made through the present investigation to determine the different flow characteristics of a converging compound channel such as velocity distribution, depth averaged velocity distribution, boundary shear etc. In this paper a complete three dimensional and two-phase CFD model for flow distribution in a converging compound channel is investigated by using Large Eddy Simulation (LES) model for solving the turbulence equation. This study aims to validate CFD simulations of free surface flow or open channel flow by using Volume of Fluid (VOF) method by comparing the data observed in hydraulics laboratory of the National Institute of Technology, Rourkela.