NUMERICAL MODELING OF FLOW IN MEANDERING COMPOUND OPEN CHANNELS

Secondary currents are important mechanisms in open channels, having major contribution in flow field and its corresponding parameters including boundary shear stress and depth-averaged velocity. Compound open channels involve extra plan form vortices in the flow field. Curved open channels generate especial vortices due to the effects of centrifugal force. Precise modeling of secondary currents in curves and meanders is a very important issue in practical applications. Using open source ``OpenFOAM'' software, the flow field in a meandering channel with compound cross section is simulated herein. Reynolds averaged Navier-Stocks equations (RANS) are solved. Applying appropriate boundary conditions over the free-surface, the simpleFoam solver has been used to model the two-phase air-water flow interface, assuming a steady flow condition, and a symmetry boundary condition. The experimental data from FCF belonging to University of Birmingham is selected for verification and validation of the present numerical results. Two turbulent models of Realizable k−varepsilon and SST k−omega are applied. Lateral velocity profiles at the cross sections indicate that at each wave-length of a meander, a vortex forms in the main channel at the apex, directing towards the outer bank near the bed and towards the inner bank near the water free-surface. The secondary current patterns, achieved for curved compound open channels differ from those of the simple channels. This is partly due to the interaction of shear stresses occurring at the interfaces between the main channel and the floodplains. Deviation of paths of the main channel and floodplains, downstream of each apex, results in entering the flow from inner bank to the main channel and exiting the flow from the main channel to the outer bank. These flow patterns shift the flow from inner- to the outer bank, downstream of each apex. Therefore, a helicoidally secondary current pattern forms, growing in size and strength farther downstream of the apex region.