Author(s): X. Shen; M. Oertel

Linked Author(s): Mario Oertel

Keywords: Cycle number; Energy dissipation; Flow characteristics; Piano key weir; Scale effect

Abstract: In the past two decades, increasing numbers of piano key weirs (PKW) have been constructed due to their sufficient hydraulic performance and optimized space requirements. Extensive experiments and numerical studies have been carried out to identify the optimal geometry and maximize the discharge capacity. However, less attention has been paid to address energy dissipation processes and the flow structure downstream, especially for in-channel applications. Within the present study, symmetrical trapezoidal piano key weir models were fabricated in two model sizes with different cycle numbers via a 3D printing technique. Both models were tested under equivalent hydraulic conditions to investigate the potential influence of the cycle number and model size regarding energy dissipation processes and the flow structure downstream of the weir. Data show identical downstream residual energy for both investigated weirs, indicating that a model with 30 cm weir height and single cycle is able to deliver reasonable results in terms of total energy dissipation. However, the flow structure downstream of the weir was observed to differ with actual weir size and cycle number, indicating that small-scaled models with an insufficient cycle number may not be able to represent a similar outflow characteristic as the prototype. Sufficient cycle number was found to be beneficial for a more stable downstream flow condition. To facilitate practical design of geometrically similar weirs, observational insights of downstream flow condition development have been provided and analytical equations have been proposed for localization of aerated flow region as well as residual energy estimation.

DOI: https://doi.org/10.26077/2d70-9137

Year: 2022