HYDRAULIC CHARACTERISTICS OF FLOW IN SIPHON SPILLWAY BASED ON NUMERICAL MODELING

Spillways are used in dam projects to convey flood flows and prevent destructive damages of downstream hydraulic systems, while the construction of other types of spillways is restricted, or there is a need to pass great values of flood discharge with a limited head. Siphon spillway is a kind of dam spillways employed in a number of dam reservoirs. This spillway is applied while the space for constructing other types of spillways is restricted, or when there is a need to pass great values of flood discharge with a limited head. One of the most important defects of this spillway is a complicated fluid-structure interaction due to the establishment of different flow regimes inside the spillway. This situation becomes more complicated when the spillway is not connected to the dam, working individually. Despite the importance of the operation of these hydraulic structures, there is a lack of comprehensive research to investigate the hydraulic behavior of these structures and the flow field around and inside them. In the present study, different unsteady flow regimes including sub-atmospheric flow, two-phase flow, and black-water flow and their effects on the hydraulic characteristics of siphon spillways were investigated. For this purpose, ANSYS CFX software was applied to simulate the flow field in such spillways. To validate the obtained flow regimes, via numerical modeling, experimental results of the former studies were used. Results indicated that the pressure fluctuations were mostly greater beneath the inlet and throat of the spillway compared to the other sections.