An experimental investigation of the influence of zigzag walls in the stilling basin on the hydraulic jump's properties

Objective: The objective of this study is to assess how stilling basin wall geometry (smooth vs. zigzag) affects hydraulic jump behavior and energy dissipation.It also investigates whether zigzag walls improve supercritical-to-subcritical flow conversion, reduce downstream scour, and support shorter, more efficient basin designs. Method: The study used two stilling basin models in a hydraulic flume at the University of Babylon: Case ۱ with smooth walls and blocks, and Case ۲ with zigzag walls and the same blocks. Twenty-two runs (۱۱ per case) were tested with discharges of ۱۰–۲۰ L/s, maintaining supercritical inlet Froude numbers of ۴.۳۰–۵.۷۰, and energy dissipation and downstream Froude numbers were measured for comparison. Results: The results indicate that the average relative energy dissipation reached ۶۱.۱% in Case ۱ and ۶۴.۹% in Case ۲, demonstrating a ۳.۸% increase attributed to zigzag wall geometry. Additionally, energy dissipation in the smooth-wall basin exhibited high sensitivity to changes in Fr₁, with a ۲۸.۱% variation across the tested Froude range, whereas the zigzag configuration showed much more stable performance, with only ۵.۱% variation. Case ۲ also generated lower downstream Froude numbers (Fr₂ between ۰.۴۶ and ۱.۲۰), reflecting better subcritical flow conditions. The free surface profile differed notably between cases, with Case ۲ showing lower water depths in the center than near the side walls, while Case ۱ maintained nearly uniform depths across the width. Conclusions: The study concludes that zigzag side walls significantly enhance and stabilize hydraulic energy dissipation, leading to more favorable downstream flow regimes and reduced scour potential, which directly benefits dam safety. The lower Fr₂ values observed in Case ۲ confirm improved compatibility with natural river flow conditions. The higher dissipation efficiency also suggests that zigzag geometry can help reduce the required length of stilling basins, offering a design advantage in both performance and economy. Although the zigzag walls create a non-uniform free surface profile, this behavior contributes positively to increased energy losses. Overall, the findings support the adoption of zigzag walls with middle blocks as an effective option for optimizing stilling basin performance and reducing structural dimensions.

کلیدواژه ها:

energy dissipater ، free surface profile ، Hydraulic jump ، spillway ، Stilling basin