عنوان مقاله [English]
In the present study, the effect of sill on the discharge coefficient (Cd) of radial gates in a free flow condition has been investigated. Variable geometric parameters of these sills are length, upstream slope, downstream slope and sill height. In addition, the effect of sill location on Cd was investigated so that in case 1, with an open gate, the sill was located in front of the gate. In case 2, the sill is located under the gate and not in front of it. In total, 43 physical models of different shapes of sills and different sizes of sills were used. The results showed that when the radial gate is open and sills are in front of the gates (case 1), the sill operates as a barrier and reduces Cd. But in case 2, the semicircle shape has a better performance and increases Cd by about 30%. Also, the rectangular and trapezoidal sills always increase Cd. In these sills, increases in Cd depend on the sill length to its height (L/Z). Small values of L/Z increase the discharge coefficient up to 25%. Finally, for circular and semicircular sill shapes, two regression equations were presented which can be used by designers.