Analysis of flow field in open channels with a backward facing step

Computational examinations were performed on flow field in an open channel having a single backward facing step with a constant water depth of 1.5 m. The effects of the expansion ratio and the flow velocity on the reattachment length are investigated by employing two different expansion ratios of 1.5 and 2, and eight diverse flow velocities of 0.5, 1, 2, 3, 4, 5, 7.5 and 10 ms-1 in the computational fluid dynamic (CFD) simulations. Analyses were performed by using two equation turbulence closure models, namely, standard k-ε, RNG k-ε, realizable k-ε, Wilcox's k-ω and SST k-ω. Commercially available CFD software, ANSYS FLUENT, was used for simulations. The analyses have revealed that the reattachment length increases with increase in the expansion ratio, the flow velocity and the Reynolds number. The results acquired for both expansion rates and eight unlike flow velocities have shown insignificant differences from one turbulence closure model to the other. Keywords: Backward facing step, Reattachment length, expansion ratio, k-ε model, k- ω model, FLUENT.