Authors: MEHDI ADJAMI, MEHDI SHAFIEEFAR, ALİ AKBAR SALEHI NEYSHABORI
Abstract: As a compound channel is characterized by a deep main channel flanked by relatively shallow floodplains, the interaction between the faster fluid velocity in the main channel and the slower moving flow on the floodplains causes shear stress at their interface, which significantly distorts flow and boundary shear stress patterns. The distortion implies that the flow field in rivers is non-homogeneously turbulent, and that lateral transport of fluid momentum and suspended sediment are influenced by the characteristics of flow in rivers. The nature of the mechanism of lateral transport needs to be understood for the design of engineering schemes that rely upon realistic flow. Furthermore, the flow in rivers is also almost turbulent. This means that the fluid motion is highly random, unsteady, and 3-dimensional. Thus, the flow cannot be properly predicted by using approximate analytical solutions to the governing equations of motion. With the complexity of the problem, the solution of turbulence is simplified with mathematical equations. The newly developed Large Eddy Simulation 2DH FLOWER_-SD model was used to solve the turbulence problem. The successive over-relaxation method was employed to solve the numerical computation based on finite difference discretization. The model was applied to compound channels with smooth roughness. Some organized large eddies were observed in the boundary between the main channel and flood channel. At this boundary the transverse velocity profile exhibited a steep gradient, which induced significant mass and momentum exchange, acted as a source of vorticity, and generated high Reynolds stresses.
Keywords: Large eddy simulation, Compound channel, Turbulent flow, Navier-Stokes equations
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