Numerical Investigation of Secondary Flow Structures in a Gravel Bed Asymmetric Compound Channel

The efficiency of a water management system is determined largely based on its water conveyance capacity through canals. Any reduction in this capacity may result in consumers not getting sufficient water resources. Amongst many factors affecting the conveyance capacity of an open channel, one of the most significant impacts is the generation of secondary currents. The secondary flow cells are generated due to the lateral and vertical component of flow velocities. There have been many experimental and analytical investigation performed to understand the effect of secondary flow cells. However, to overcome such rigorous and time-consuming experimental procedures, numerical simulations can be applied using computational fluid dynamics (CFD). In this present study, numerical simulations have been performed to understand the impact of secondary current cells in an asymmetric compound channel. Amongst many turbulence models available in ANSYS Fluent software package, k-ω turbulence model has been selected because of its capability to provide good results with less computing resources. The numerically simulated results are validated with theoretical models. It has been observed that the numerical results confirmed well with the theoretical models. Three types of vortices, namely longitudinal vortex, free surface vortex, and bottom vortex are observed in the channel cross-section. As the flow depth increases, the vortices are shifted towards the interface of main channel and flood plain and also, they are decreased with increase of relative depth, which clearly agrees with theoretical studies. This study will be helpful to the hydraulic engineers and researchers working on the conveyance capacity of channels.