Author(s): Biruk Belay; Mario Oertel

Linked Author(s): Biruk Belay

Keywords: Piano key weir; Sidewall; Standing wave; Void fraction

Abstract: Piano key weirs offer significant advantages in terms of hydraulic efficiency due to enhanced discharge capacity and energy dissipation. Nappe interactions (within the outlet keys) and plunging jets (from the inlet keys) into a downstream pool are the critical events that lead to a highly turbulent and aerated flow. This experimental study investigates the influence of piano key weir orientation relative to the flow direction on the resulting basic air-water flow properties. Two-phase flow measurements were performed for two different weir orientations: one with a wall-adjacent inlet key and the other with a wall-adjacent outlet key. The measurements were taken at locations longitudinally adjacent to the sidewall and cross-sectionally near the inlet and outlet keys. The outcomes showed that the orientation of the weir relative to the flow direction affects the nature of the sidewall standing waves. This induced significant differences in the cross-sectional void fraction distributions and the characteristic air-water flow depths. Compared to the wall-adjacent outlet key configuration, the orientation with the wall-adjacent inlet key induced stronger sidewall standing waves with a relatively higher characteristic air-water flow depth and a smaller depth-averaged void fraction near the sidewall. These standing waves re-directed the flux of air bubbles in the transversal direction and superimposed the void fraction to the next outlet key at the inner side. In the case of the wall-adjacent outlet key orientation, the influence of sidewall standing waves on the overall cross-sectional two-phase flow properties was relatively minimal. Overall, the outcomes of this experimental investigation highlighted that the orientation of a piano key weir relative to the flow direction could dictate the required sidewall heights, which could be relevant information at design stages, especially close to jet impact zones.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1993-cd

Year: 2025