Analysis of energy loss in a C-type trapezoidal Piano key weir with outlet key jumps

Piano key weirs are a type of long-crested weirs with a light foundation and a high discharge coefficient. Due to the high efficiency of these weirs, it is essential to find ways to increase their energy dissipation and ultimately reduce scour. This study investigated the energy dissipation of piano key weirs with a jump in their outlet keys. A laboratory experiment was conducted using a trapezoidal piano key weir with three discharges of 0.3, 0.35, and 0.4 cubic meters per second. Two jumps with radii of 0.21 and 0.15 meters and jump heights of 0.14 and 0.075 meters were also used. The results showed that the energy dissipation increased with increasing jump radius. The energy dissipation in the weir with a jump radius of 0.21 meters and in the weir with a jump radius of 0.15 meters is approximately 3.8% and 2.5% higher, respectively, than in the weir without a jump. The average energy dissipation in weirs with jump radii of 0, 0.15, and 0.21 meters was 54.1%, 55.4%, and 56.2%, respectively. With increasing jump radius and jump height, the discharge coefficient decreases. The discharge coefficient in piano key weirs with jump radii of 0.21 and 0.15 meters is reduced by 10.9% and 3.9%, respectively, compared to the weir without a jump. The use of a jump in the outlet keys of a weir can throw the flow forward of the weir toe. This can be effective in reducing scour.