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.

Nonuniform Flows in a Compound Open‐Channel: Assessment of a Hybrid RANS‐LES Approach

“…The second tool available is the Large Eddy Simulation (LES), which is used to investigate and describe the turbulent structure of uniform flows in straight compound open‐channels (Cater & Williams, 2008; Kara et al, 2012; Thomas & Williams, 1995; Xie et al, 2013). LES is also used to investigate flows in nonprismatic compound channel geometries, like a compound channel with converging FPs (Mohanta et al, 2015), meandering main channels (Moncho‐Esteve et al, 2018), and bridge abutments over FPs (Vui Chua et al, 2019). However, due to a relatively high computational cost related to spatial resolution requirements, most LES studies use periodic boundary conditions or focus on specific channel areas with precursor simulations to define the inlet flow (Vui Chua et al, 2019).…”

Validation of Computational Fluid Dynamics Approach of Lateral Velocity Profile Due to Curvature Effect on Floodplain Levee of Two-stage Meandering Channel

“…Various studies have investigated the lateral velocity profile, sharing of depth averaged velocity as well as shear force, transference of momentum, and discharge calculation in meandering compound channels ([1]; [2]; [3]; [4]; [5]; [6]; [7]; [8]; [9]; [10][11][12][13][14][15]). Also numerous investigations were carried out to examine the flow pattern at channel confluence considering various geometrical parameters by using numerical methods ( [16]; [17]; [18]; [19]; [20]; [21]; [22]; [23]; [24]; [25][26][27]). Kiely [4] and McKeogh and Kiely [28] investigated on compound channels and concluded that the high turbulence intensities were seen in floodplain area of compound meandering channel than straight compound channel in longitudinal direction.…”

“…Afzal et al [34] studied the roughness factor and turbulent effect in roughed pipe and channels through power law of velocity profile. Lane et al [26] performed CFD analysis by changing bed topography and roughness on gravel-bed River and also evaluated wall roughness height in individual cells based on cell porosity and technological capabilities. Carney et al [27] investigated natural channels with substantial bed roughness to offer a strategy to mitigate the coarse bed utility through CFD analysis.…”

“…Mohanta et.al. [25][26][27] studied non-uniform flow and their effect on velocity and boundary shear distribution through experimental as well as Large Eddy Simulation (LES) turbulence model in numerical CFD approach on converging compound channel. The semi-logarithmic relationship between velocity and distance from the wall is characterised as the 'law of wall,' which exists outside the laminar zone.…”