FLOW MODELLING OF NON PRISMATIC COMPOUND CHANNEL USING ANSYS

Abstract

Flooding situation1in river is1a complex phenomenon1and affects the livelihood1and economic condition1of the region. The1modeling of such flow1is primary importance for1a river engineers and scientists1working in this field. Water surface prediction1is an important task in flood1risk management. As a result of topography1changes along the open channels, designing the1converging compound channel1is an essential. Fluvial flows1are strongly influenced by geometry1complexity and large overall uncertainty1on every single measurable1property, such as velocity distribution1on different sectional parameters like width1ratio, aspect ratio and hydraulic parameter1such as relative depth. The geometry selected1for this study is that of a1prismatic compound channel1having converging flood1plain. For the research work1the parameters, the water1depth, incoming discharge of the main1channel and floodplains were1varied. This total topic represents1a practical method to predict1lateral depth-averaged velocity1distribution in a prismatic compound1channel. Compound section of a natural1channel generally comprises a1wider and rougher flood plain1than main channel. The flow1process in the open channel becomes more complicated1at over bank stages due to the different1hydraulic condition prevailing in the main1channel and the adjoining flood1plain. As the shallow flood1plains offer more resistance1to flow than the deep main channel, the1velocity tends to be higher1in deeper main channel than the shallow1flood plain. This variation of velocity1between deep main channel section and the adjoining1shallow flood plains raise the lateral1momentum transfer, which further complicates1the flow process. In the present work an experiment for the depth average velocity1at different points of the channel1cross section in lateral direction1is carried out by using1ADV, for a compound channel having width1ratio 2.923 V

with differential roughness1(the ratio of base n value of flood plain surface1roughness to main channel roughness)12.0833m^(-1/3)sec. The numerical model using ANSYS1fluent as a result of developing simulation1model for velocity and flow depth are compared with laboratory data for flow1in a compound channel that consists1of a main channel and symmetric flood plains1set at a fixed bed slope. Reasonable1agreement between the numerical results1and experimental data is shown for steady1uniform flow located at a section at a distance1of 8.5m from the start end. Computational Fluid Dynamics (CFD)1is often used to predict flow structures1in developing areas of a flow1field for the determination of velocity, pressure, shear1stresses, effect of turbulence and1others. This study aims to validate1CFD simulations of free surface flow or open channel1flow by using Finite Volume method by comparing1the data of the past research done in NIT Rourkela by K.K.Khatua.