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Air-entrainment and detrainment processes in tailrace channels downstream of Pelton turbines were investigated in a physical laboratory model of the new hydropower plant Veytaux 2, Switzerland. These processes are mainly influenced by the emergent jet velocity of the Pelton turbine and the resulting air entrainment to the water cushion due to high-speed jet impact. The air demand in the turbine housing, and the air concentration and velocity distributions in the tailrace channel are analyzed. The project-specific results are generalized by additional investigations involving a simplified model geometry. A comparison with previous model and prototype data is presented. The results indicate that the deaeration length relative to the tailwater flow depth depends mainly on the jet Froude number made up by the emergent jet velocity relative to the tailwater propagation velocity, plus the water discharge, the tailwater cross-sectional area, and the presence or absence of a flow straightener at the tailrace-channel entrance. [ABSTRACT FROM AUTHOR]