Numerical Analysis of Turbulent Flow over a Backward-facing Step in an Open Channel

Abstract

Computational examinations of the flow field in an open channel having a single Backward--Facing Step (BFS) with a constant water depth of 1.5 m were performed. The e ects of the expansion ratio, and the flow velocity along the reattachment length, were investigated by employing two di erent expansion ratios of 1.5 and 2, and eight various flow velocities of 0.5, 1, 2, 3, 4, 5, 7.5 and 10 m/sec in the Computational Fluid Dynamic (CFD) simulations. Commercially available CFD software, ANSYS FLUENT, was used for calculations. The simulation outcomes were verified using experimental results. Moreover, analyses were performed by using two equation turbulence closure models, K-ɛ family (standard, RNG and realizable), and K-ω family (Wilcox’s and SST K-ω). The analyses have revealed that the reattachment length increases with an increase in the expansion ratio, the flow velocity and the Reynolds number. The results obtained for two expansion rates and eight di erent flow velocities have shown insignificant di erences between one turbulence closure model and the others. Furthermore, it was observed that both velocity and expansion ratios have an e ect on the reattachment zone size.