The purpose of this study is to investigate the flow pattern and discharge coefficient of sluice gate with the non-suppressed sill in experimental and numerical conditions. For this purpose, the sill of a rectangular cube in widths of 7.5, 10, 15, and 20 cm was installed under the sluice gate. Experimental results showed that placing a non-suppressed sill under the sluice gate by creating a failure in the flow lines causes a different flow pattern compared to the without sill state. Deviation of streamlines after colliding with the sill causes the formation of V-shaped currents. The discretization of equations for simulations were performed using VOF method. After selecting a cell with a size of 0.07 cm as the optimal cell, the RNG turbulence model was used. The results of the numerical simulation showed an acceptable agreement with the experimental results. Thus, the place of formation of V-shaped currents was transferred downstream of the sluice gate by increasing the width of the sill and the inflow discharge. The results of the study of the discharge coefficient showed that the placement of the sill with a width of 7.5 and 20 cm, increased the discharge coefficient by an average of 5.3% and 15.5% in the experimental model and 4.7% and 16% in the numerical simulation. This relationship is without sill state and with sill state with root mean square error of 0.967 and 0.968, respectively, estimated the discharge coefficient of the sluice gate.
