Author(s): Usman Ghani; Xiaonan Tang
Linked Author(s): Usman Ghani, Xiaonan Tang
Keywords: Numerical modelling; Checker-board bed configuration; Periodic boundary condition; Roughness; Open channel flow
Abstract: Boundary condition setting is prerequisite and most important in numerical modelling of computational fluid dynamics. If boundary conditions used in the simulation work are not a true representative of the actual flow situation, then results obtained will be unrealistic. One of the boundary conditions that can be used in open channel flows is periodic boundary condition. This boundary condition can reduce CPU time by running a small computational domain rather than a large domain. However it can only be used in certain cases such as when the flow has the same features periodically. In this paper the periodic boundary condition has been used to examine its suitability at the inlet and outlet of a flow domain chosen for two different heterogeneous bed configurations in open channel flow. One bed formation consisted of two parallel longitudinal strips of smooth and rough beds while the other one was a checker-board like bed configuration. A 3D numerical code FLUENT has been used which solves three dimensional Reynolds Averaged Navior-Stokes equations using finite volume technique. It was revealed that the periodic boundary condition results in fully developed flow phenomenon in a very small computational domain. This boundary condition captured the periodicity of the flow structure. For comparison, the same simulation work was undertaken using commonly used boundary conditions, i. e. velocity inlet and pressure outlet boundary conditions along with actual length of the channel, which usually has large computational domain. The simulation made using both boundary conditions yielded similar results. This study shows that the periodic boundary condition is an appropriate boundary condition to be used for modelling flow in bed formations with varying lateral roughness in open channel flows.
Year: 2013