Experimental determination of contraction coefficient and velocity coefficient for radial gates with elliptical lips

摘要

Radial gates are widely used to control the flow in irrigation channels and spillways. Radial gates require lower hoisting force and have better discharge characteristics in partial gate openings. The accurate discharge measurement through a radial gate is a challenging problem especially in submerged flow conditions. The coefficient of contraction C-c is an important parameter for accurate discharge measurement in open channels. In this study, an attempt has been made to determine the coefficient of contractionC(c) and velocity coefficient C-v for radial gates both for free flow and submerged flow conditions. The flow emanating from a gate is similar to the wall jet emerging from a nozzle. The C-c and C-v values under free and submerged flow conditions are obtained from the measured jet velocity and the discharge. The coefficient of discharge values under submerged flow conditions show large variations with submergence and hence discharge characteristics needs to be improved for better control of flow. Hence, experiments are conducted so as to improve the discharge characteristics by modifying the exit geometry of the radial gate by attaching a quarter of an elliptical lip. Three different geometries of elliptical lips were attempted and the results show reasonable increase in the contraction coefficient.