Exploring Two-Phase Flow Dynamics: Experimental Investigations and Computational Modeling in Smooth and Stepped Chutes

Cavitation damage to concrete structures is common in dam spillways. Cavitation can lead to cracks on the concrete surface which further increases the risk of damage to concrete by means of sulfate attack, freeze-thaw, alkali-silica reaction, and others. Cavitation damage occurs on concrete surfaces when discontinuities or irregularities are encountered in the path of high speed water flow. Stepped spillways are suitable, economic options for high-volume storage dams that require significant energy dissipation, for structural adaptations to roller-compacted concrete dams, and to promote spontaneous flow aeration. In this study, numerical analysis of the hydraulic characteristics for the skimming flow regime of over the stepped spillway of the Zirdan Dam is carried out. A comparison between the flow characteristics for stepped and smooth spillways is provided. By preparing numerical models using the k-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 was 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. For the design discharge, the difference in energy dissipation for the stepped and smooth spillway is 47%.