Author(s): Biruk Belay; Mario Oertel
Linked Author(s): Biruk Belay, Mario Oertel
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 conducted in the aerated region longitudinally adjacent to the sidewall, and cross-sectionally in front of the neighboring outlet and inlet keys for two different weir orientations with (1) a wall-adjacent inlet key, and (2) a wall-adjacent outlet key. The outcomes showed that the orientation of the weir relative to the flow direction highly affects the nature of the sidewall standing waves. This induced significant differences in the cross-sectional void fraction distributions and the characteristic flow depths. In comparison, the orientation with the wall-adjacent inlet key induced stronger sidewall standing waves with a higher characteristic mixture flow depth and reduced depth-averaged void fraction near the sidewall. The 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. Conversely, 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 less adverse. 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.
Year: 2025