Numerical Study of Backward Facing Step Flow over Various Step Angles and Expansion Ratios

Abstract

To study the flow over hydraulic structures such as weirs, dams, sluice gates, etc., a single-sided backward-facing step is a fundamental configuration in order to investigate the flow pattern including turbulence structures, separation, and reattachment length. The separation zone plays an important role on the energy dissipation and scouring after the steps. In this study, two-dimensional numerical simulations of flow over the backward-facing step with various step angles and expansion ratios have been carried out. An open source program OpenFOAM was used for the computation. RANS approach was applied for turbulence calculation, in order to determine a better approach for a specific application. Numerical results have been validated against Ruck et al and Nakagawa et als experiments. The step angles varied from 10 to 45 degree. The results showed a good agreement with experiments on the major flow patterns, however at the low Reynolds number flow, RANS model showed a worse agreement. For the real application, Sejong weir was chosen as a case study. In this study, the reattachment length was increased as the step angle increases.