Trajectories and air flow features of ski jump-generated jets

ABSTRACT

Ski jumps are frequently applied as spillways of high dams. The resulting jet impact location on the plunge pool surface is often distant from the dam toe so that the latter is protected from scouring. Furthermore, the jet disintegrates and disperses prior to its impact, thereby reducing the specific energy addition to the plunge pool. The present research addresses four aspects, based on three physical modelling campaigns: (1) geometry of upper and lower jet trajectories; (2) virtual jet take-off angles for the trajectory computations; (3) average and minimum cross-sectional air concentrations along the jet; and (4) general jet air concentration profiles. It is shown that the trajectory parabola may also be applied for negative jet take-off angles, and that these are smaller than the bucket angle. As for the air concentration distribution along the jet, tests indicate that the latter depends exclusively on the relative jet black-water core length.

Keywords:

• Air concentration
• flip bucket
• jet
• ski jump
• trajectory

Acknowledgements

Dr Valentin Heller, Imperial College London, is kindly acknowledged for having made available the raw data of his research to the authors. The authors further thank Dr Lukas Schmocker, Basler und Hofmann AG Zurich, and Mr Andrea A. Balestra, formerly ETH Zurich, now at Lombardi Engineering Minusio, for having provided their data sets.