NUMERICAL SIMULATION OF MEANDERING OPEN CHANNEL FLOWS
Usman Ghani*, Naeem Ijaz* and Daulat Khan**
ABSTRACT
Flooding occurs worldwide and causes huge loss to human life and property. There is an ever increasing danger of floods due to global warming. The overbank flow studies are important for understanding flow behavior and bed shear stresses during floods and for devising flood protection strategies. This study is based on three dimensional numerical simulation of overbank flows in meandering channels. Four different flow cases were considered. The cases vary from each other in the sense of bed slope and overbank flow depth. There were two overbank flow depths for each bed slope. In this study a rectangular main channel flanked by floodplains on both sides has been considered. The simulation was carried out by solving 3D continuity and Reynolds averaged Navior Stokes equations using a finite volume based numerical code. The turbulence closure was achieved through standard k - turbulence model. A comparison of simulated primary depth averaged velocities and conveyance capacities of main channel with experimental results were made and good agreement was achieved. The simulations were also made for stream-wise velocities and secondary velocity vectors over different sections along the meander wavelength for the four cases to enhance the understanding of the primary and secondary flow fields and boundary shear stresses using numerical simulation. It was observed that the direction of secondary currents depends upon flow depth and their strength increases with increasing depth of flow. In compound channel flow cases, the overbank flow velocities are stronger than the inbank flow field. The bed shearing stresses at the apex of the meander were also found to have been under the influence of flow depth and secondary circulations. It was also established that standard - turbulence model which is incapable of simulating straight channels flows can simulate meandering channels to good accuracy.
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December 2012
Vol 31 No 2 (2012)
