Two-dimensional analysis of flow patterns around a single backward-facing step

Abstract

A depth-averaged two-dimensional (2D) numerical model is applied to predict the flow over a single backward-facing step. The model is established using the finite-volume method on a curvilinear grid. The 2D basic governing shallow water equations used in the generalized curvilinear coordinate system are solved. This paper focuses on the generation of shockwaves and hydraulic jumps downstream of the step, in addition to the depth of the supercritical stream immediately downstream of the step. Such flow features occur because of the sudden change in the geometry of the channel, such as the abrupt expansion in the flow cross-section. The backwater effect due to in the water depth downstream the step is also considered. Six experimental cases are carried out with a water-free-fall step, a partially submerged step and fully submerged step. By comparing the numerical results with observed laboratory experimental results, the model is capable of reproducing the above-mentioned flow features, and shows a good agreement with the measured data. This study analyses the flow over a backward-facing step, better knowledge of which can reduce flood risk problems in urban rivers.

Keywords:

• Two-dimensional numerical model
• backward-facing step
• shockwaves
• hydraulic jumps