Hydraulic of curved type-B piano key weirs characteristics under free flow conditions

Piano-key weirs (PKWs) have gained importance in recent years as an alternative to conventional weirs for controlling the flow of water in dam rehabilitation projects. PKWs have several advantages over conventional weirs, including a larger discharge capacity, improved hydraulic performance, reduced construction costs, and better resilience against extreme hydrological events. There have been several studies in recent years that have focused on optimizing the design of curved PKWs to enhance their hydraulic characteristics. Curving the conventional weir crest has been shown to be an effective way to increase its discharge capacity and improve hydraulic performance compared to conventional weirs. The aim of this study is to investigate the hydraulic characteristics of PKWs to improve their discharge capacity. The study focuses on the 2-unit and 4-unit types of the curved Type-B PKWs (central convergence angles of 90° and 130°) under various head conditions. Experimental and numerical methods were used to analyze the water surface profiles, flow streamlines, and velocity fields. The results showed that curved weirs have better discharge capacity compared to non-curved types. The numerical results were in agreement with experimental data and revealed that the 130° PKW had a higher discharge coefficient under low-head conditions due to reduced contraction of streamlines in the inlet keys and reduced scale of separation bubbles entering the inlet keys. The results also demonstrated that under low-head conditions, the discharge coefficients of 2-unit and 4-unit 130° PKWs respectively increased by 17.69% and 18.85%, when compared to conventional weir performance, respectively. These findings can be useful for dam rehabilitation projects to improve the control of flow rates and water surface profile upstream of the weir.