Numerical Simulation of the Effect of Channel bed Slope on the Hydraulic Performance of Sharp-Crested Rectangular Side Weir with Subcritical and Supercritical Regimes

Side weirs are types of hydraulic structures, which are used for different purposes in water transmission systems. In most of the construction operations of irrigation channels and water transfer, based on the topographic conditions of the land, the bottom of the channels is sloped. The purpose of this research is to numerically investigate the changes in the slope of the bottom bed and evaluate the performance of the side weirs in flood conditions and supercritical and subcritical flow regimes. To simulate the flow, CFD method and FLOW-3D® software and RNG turbulence model were used. By examining the surface profile of the flow passing through the weirs at different bed slopes, it was observed that in a fixed slope, in the subcritical flow regime, the surface profile trend is increasing from the beginning to the end of the weir, and decreasing in the supercritical flow regime. As the slope of the main channel bed increases, the level of flow passing over the weir decreases. On average, by changing the regime from subcritical to supercritical, the weir efficiency decreased by 11.21%. Increasing the bed slope decreased the weir efficiency and discharge coefficient in the subcritical flow regime up to 14.54% and in the supercritical flow regime up to 9.26%. The increase in discharge coefficient with the increase of the weir height varied between 4.6 and 7.8 percent. With the increase of the slope of the channel bed, the velocity along the weir in the subcritical and supercritical flow regimes increased by 10.88 and 6.17%, respectively, and the transverse velocity decreased by 22.23 and 4.8 percent, respectively for the subcritical and supercritical flow regimes.