Affection of Side Contraction on Discharge Coefficient in Chimney Weir using Numerical Simulation

Quadratic weir is one of the unique types of available thin plate weirs that can be used for flow measuring in water transmission channels, irrigation networks and urban runoff networks because of its unique capabilities. In this research with the aim of investigation the effect of side contraction ratio on discharge coefficient of this weir, the flow through a quadratic proportional (chimney) weir in a rectangular channel with 10 bed widths and with side openness ratios of 10 to 100 percent, is simulated in 3D by ANSYS FLUENT software and has been calibrated using similar laboratory results. After measuring of water depth at the upstream channel for different passing discharges in each channel widths, The average of discharge coefficient in range of water depth between two to three times the height of triangle basin was calculated and results showed that in side openness ratio between 10 to 30%, the discharge coefficient value was 0.6 with no change, but with the increase in the cross-sectional openness ratio from 30% to 100%, the discharge coefficient increased and its final value in the 100% openness was 0.65. Finally an experimental relationship was proposed to correct the discharge coefficient based on the side openness ratio.