Effects of a conical enlarging shaft on hydraulic performances of siphon-shaft spillways

Abstract Siphon-shaft spillways can discharge large amounts of water down to the crest level in a narrow reservoir thanks siphonic pressures. However, cavitational pressures siphon-shaft limit operating head these spillways. An enlargement at shaft mouth reduce vacuum and velocities within flows, thereby removing risk cavitation occurring. In this study, four different enlarging profiles with various coning angles 0°, 10°, 15°, 20° were applied spillway model eliminate shaft. These models are analyzed three dimensions by computational fluid dynamics based on RANS turbulence coupled Volume Fluid (VOF) method simulate motion. The numerical uncertainties simulation calibrated some experimental results techniques literature. showed that conical profile significantly decreased siphon-shaft. Thus, use considerably reduced numbers along surface increased performance about 11%.