Numerical simulation of aeration impact on the performance of a-type rectangular and trapezoidal piano key weirs

One of the challenges associated with Piano Key Weirs (PKWs) is the nappe oscillation of the flow passing over them. Aeration of the flow has been identified as an effective method to mitigate this oscillation. This study aimed to explore the impact of varying dimensionless aerator ratios (defined as the ratio of the aerator area to the projected area of the inlet key face) and their positions on the flow dynamics and discharge efficiency of Type-A rectangular and trapezoidal PKWs, RPKW and TPKW respectively. To this end, PKWs were numerically modeled under various aeration conditions and upstream heads. In the modeled geometry, an aerator duct was positioned beneath the inlet apex and either pressurized or natural aeration was applied as its boundary condition. The study also investigated the streamlines of the incoming flow and the potential spots for installing splitters (as alternatives to aerators) on the overhang corners. Additionally, the effects of aeration on the discharge coefficient were examined for Type-A of RPKW and TPKW. The findings indicated a maximum permissible aeration level in PKWs, suggesting that aerators should not be oversized in this weir. Further, the study reveals that in TPKW, the aeration ratio does not have much effect on the discharge efficiency, hence the installation of an aerator is not recommended. In contrast, for RPKW, an aeration ratio up to a maximum of 3% is suggested. It was also observed that aeration influenced the trajectory of the water jet and the oscillation of the nappe in PKWs.