Discharge Characteristics of Semicylindrical-Edged Vertical Sluice Gates

Sluice gates are used in open channels, such as irrigation canals, as an undershot structure for letting out controlled discharges and regulating the upstream water level. This necessitates a precise estimation of the coefficient of discharge (Cd) for both free and submerged flow conditions. The addition of a semicylindrical drum as a lip to the upstream side of a vertical gate is seen to significantly increase Cd, and this paper investigates its characteristics with changing drum diameter. Data on channel velocity and gate pressure obtained from experiments carried out on a physical model are used to validate a computational fluid dynamics model, which is then repeatedly run to generate further data for relating changes in Cd to varying flow parameters. The contraction coefficient (Cc) is seen to increase by 43.2–52.3% upon adding a semicylindrical lip, which may be explained by the zero streamline angle at the edge of the lip. The relation between simulated Cc and Cd for three semicylindrical lips confirms that an increase in Cd with increasing lip diameter is primarily due to the improved straightness of the streamlines, as evidenced by the simulated velocity components at the gate opening. Meanwhile, reduction in energy loss due to turbulence plays a secondary role in increasing Cd. As a corollary, for a given Froude number of flow at the gate, the difference in upstream and downstream heads under submerged flow conditions reaches a maximum for a gate without a lip and reduces with increasing lip diameters. It is also observed that, for a given lip diameter, Cd reduces if the semicylinder is truncated to a quarter of a circle sector and decreases further for smaller arc angles.