Developing and testing a novel pressure-controlled hydraulic profile for siphon-shaft spillways

The operating heads of the siphon-shaft spillways are limited by cavitational pressure due to low siphonic pressure inside the spillway shaft. Therefore, these low pressures inside the shaft must be eliminated to control the cavitation. An innovative idea is to enlarge the shaft cross-section upwards where siphonic pressure decreases. For this purpose, in this study, a new pressure-controlled siphon-shaft profile was developed analytically based on Bernoulli principle and cavitational pressure. The hydraulic performance of the profile is numerically tested by means of computational fluid dynamics (CFD). The numerical model used was validated with the results of a benchmark model, and the discretization errors were estimated based on a procedure recommended by American Society of Mechanical Engineers (ASME). The verified models used to analyze the novel hydraulic design together with the classical Wagner profile originally applied to shaft/morning glory spillways. The analysis results indicated that the pressure-controlled siphon-shaft profile is quite effective in terms of cavitation protection and hydraulics performance for siphon-shaft spillways.