Abstract
Gabion weirs are environmentally friendly hydraulic structures that regulate floods and reduce bottom erosion by controlling flow velocity. This study aims to simulate the flow over gabion stepped weirs numerically. A three-dimensional simulation has been conducted using ANSYS Fluent software (ANSYS 2021 R1). A computational fluid dynamics (CFD) model utilizing the volume of fluid (VOF) technique with (Standard, RNG, and Realizable) k-Ɛ, and Standard k-ω turbulence models have been used. A laboratory-scale of gabion stepped model with a downstream slope of (1:1, 1:2, and 1:3 V: H), and porosity (0.42) was used to verify the numerical models, for three operational discharges (3.08E-3, 23.26E-3, and 52.63E-3) m3/s. The downstream velocity was used to verify the numerical models. The results showed that all models agree with the experimental data. The root means square error (RMSE) values ranged between 0.14 and 0.309 and the determination of coefficient (R2) values ranged between 0.965 and 0.812, where the standard k-Ɛ model was the most representative of the flow condition and downstream velocity. The Turbulent Kinetic Energy (TKE) of a stepped gabion weir with a porosity of 0.42 and a slope of 1:2 was predicted. The results showed that the TKE values increased in the lower regions at the skimming flow regime, where the k-ω model showed the highest turbulence levels compared to the other models. Moreover, at the nappe flow regime, TKE peaks on the weir steps due to the generated eddies, while low discharges (through-flow regime) showed relatively stable flow. Furthermore, according to predicted streamlines, the porous medium reduces the flow velocity and the emergence of up-and-down flow at the weir crest. The effect of turbulence and seepage increases at high discharge, while turbulence decreases and flow lines become straighter at low discharge.