Abstract
Siphon-shaft spillways are constituted by covering above a shaft spillway with a hood that creates siphonic pressure. This study focused on the aeration the flow through the aerator holes placed on the hood to prevent cavitational damage in high-head siphon-shaft spillways. Three-dimensional computational fluid dynamics (CFD) technique using finite-volume method to solve Reynolds-averaged Navier–Stokes (RANS) equations for the incompressible viscous and turbulent fluids motion was performed to analyze the full-scaled two-phase numerical models. The volume of fluid (VOF) scheme was used to simulate two-phase (water–air) flow, by defining the volume fraction for each of the fluids throughout the solution domain. The accuracy of the numerical model was tested using a procedure recommended by American Society of Mechanical Engineers (ASME) for CFD applications. The numerical results showed that the aeration is highly effective in reducing siphon sub-pressures and cavitation. The optimal relative aeration diameter of 0.45 provided sufficient air entrainment to protect from cavitation and did not decrease the discharge performance too much.
Highlights
Siphon spillways are used to pass more discharges at lower crest head than free napped spillways through its siphonic sub-atmospheric pressures
There is no risk of cavitation, there is no need for air entrainment, and at the same time the discharge capacity does not reduce due to air intake
Page 11 of 12 165 the risk of cavitation were analyzed by the reliable computational fluid dynamics (CFD) models
Summary
Siphon spillways are used to pass more discharges at lower crest head than free napped spillways through its siphonic sub-atmospheric pressures. Siphon spillways have the advantage of a great sensitivity at the rise of the water upstream level and the great discharge per length of sill (Houichi et al 2009). Siphon-shaft spillway as a hybrid type combines the advantages of siphon and shaft spillways. Since the velocities in the cross section are higher due to the siphon effect, the same flow discharge can be transferred with smaller sections in siphon-shaft spillways compared to the shaft spillways. The weir discharge is not affected by the water level in the reservoir as much as free over-flow spillways. Vortex effects are less than free surface shaft weirs, as the siphon head prevents the free vortex. There are some disadvantages such as limited capacity, so it is recommended to plan it with an auxiliary spillway to be used when necessary (Agiralioglu, 1977)
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