Hydraulic characteristics of flow over stepped and chute spillways (case study: Zirdan Dam)

Abstract

Stepped spillways are suitable and economical options for high-storage dams that require significant energy dissipation, structural adaptation to roller-compacted concrete dams, and spontaneous flow aeration. In this study, a numerical analysis of the hydraulic characteristics for the skimming flow regime of the stepped spillway of Zirdan Dam is carried out. A comparison between the flow characteristics for stepped and smooth spillways is provided. By preparing numerical models of the spillway using the k-ε RNG turbulence model and the multiphase mixture method, a hydraulic analysis of the flow was completed. To verify the performance of the numerical model, field data were collected and used for validation. The results show that the presence of steps along the spillway cause a significant reduction in the length of the boundary layer and faster aeration occurs. In a stepped spillway, the cavitation index is higher than the critical limit along the entire length of the spillway. Thus, the risk of cavitation and destruction is negligible. On the other hand, with a smooth spillway, the possibility of cavitation may occur. This negative effect (negative pressures) occurs 56 m from the crest of the spillway on the downstream side. HIGHLIGHTS The presence of steps along the spillway causes a significant reduction in the length of the boundary layer.; In a stepped spillway, the cavitation index is higher than the critical limit along the entire length of the spillway.; The negative pressures occur 56 m from the crest of the spillway on the downstream side.; The difference in energy dissipation on the stepped and smooth spillway is 47%.;

Keywords

• cavitation index
• energy dissipation
• numerical modeling
• stepped spillway
• turbulence model