CFD modeling of the effect of various characteristics of Semi-Circular Labyrinth side weirs on the discharge coefficient

Side weirs are fundamental components in open-channel hydraulic systems, serving critical functions such as regulating excess flow, enabling controlled water diversion, and mitigating flood risks in both agricultural and urban environments. Their design directly influences the efficiency and safety of water conveyance infrastructure. Among various configurations, labyrinth side weirs particularly those with curved geometries offer enhanced discharge capacities due to increased effective crest length within limited channel space. This study evaluates how the crest height of a two-sided, semi-circular labyrinth side weir affects both the discharge coefficient and the water surface profile. The investigation is conducted in three dimensions using Ansys Fluent software. Side weirs with three, four, and five cycles; 10, 15, and 20 cm heights; and an opening length of 40 cm are used. The discharge coefficient and water surface profiles are analyzed and compared to experimental results. The calculated values showed a strong agreement with the experimental data, and the error ranged from 0% to 7.5%. Based on the findings, each 20% decrease in side weir height causes the level drop to decrease by 15%. Also, the side weir discharge coefficient decreases with increasing side weir height and upstream Froude number; furthermore, the discharge coefficient increases with rising numbers of labyrinth cycles. Therefore, a five-cycle, semi-circular side weir with a height of 10 cm has a higher discharge coefficient than the other studied spillways. These results contribute valuable insights for hydraulic engineers engaged in the design and optimization of side weirs, offering evidence-based guidance for improving flow regulation structures. The findings support the adoption of geometrically efficient labyrinth designs in water management projects where spatial constraints and flow variability are key considerations.