Saltos En Sky

Ski Jump Hydraulics

J. Hydraul. Eng. 2005.131:347-355.
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Valentin Heller1; Willi H. Hager, F.ASCE2; and Hans-Erwin Minor3
Abstract: Ski jumps are a major element of each dam spillway becausethese are the only structures able to accomplish satisfactory
energy dissipation for takeoff velocities in excess of some 20 m / s. This research aims to add to several hydraulic problems with ski jumps
that have not yet been systematically solved so far. Based on an experimental campaign, the following problems were addressed: 1
pressure head maximum and pressure distribution along acircular-shaped flip bucket; 2 takeoff characteristics for a certain bucket
deflection and a relative bucket curvature including the jet trajectories of both the lower and the upper nappes; 3 impact characteristics
in a prismatic tailwater channel with details of shock wave formation and height of recirculation depth; 4 energy dissipation across the
ski jump, from the upstream channel to downstream of jetimpact; and 5 choking flow conditions by the flip bucket. These results
demonstrated the significant effect of the approach Froude number, the relative bucket curvature and the bucket angle. The results allow
immediate application to the design of ski jumps in hydraulic engineering.
DOI: 10.1061/ ASCE 0733-9429 2005 131:5 347
CE Database subject headings: Hydraulic jump; Spillways; Velocity; Energydissipation; Hydraulic engineering.

Introduction
Energy dissipation downstream of large dams is a serious concern. Trajectory spillways or so called ski jumps are employed
whenever the velocity at the dam foot is in excess of typically
20 m / s because of problems with stilling basins in terms of cavitation, abrasion and uplift Vischer and Hager 1995 . Ski jumps
are currently widely usedbecause they appear to be the only
hydraulic element allowing for the technically sound and the hydraulically safe control of large quantities of hydraulic excess
energy during flood season.
Although ski jumps were introduced in the 1930s in France,
several questions have so far not been systematically addressed.
Out of the thousands of structures erected worldwide, most were
model-testedregardless of a general design. Standard information
such as from the U.S. Corps of Engineers or from the U.S. Bureau
of Reclamation is not available. A summary of major dam designs
with a ski jump was used to define the main parameters of the
present research Varshney and Bajaj 1970; Rajan and Shivashankara Rao 1980; Shivashankara Rao 1982 . Therefore, a research
project was conducted atVersuchsanstalt für Wasserbau, Hydrology und Glaciology VAW, ETH Zurich to fill in this gap. The
present research may be considered a continuation of Juon and
Hager 2000 , where isolated aspects of prismatic ski jump hydraulics were investigated.
This research was conducted in a prismatic channel in which a
circular-shaped flip bucket was inserted. It intended to answer
1
Diploma Student, VAW,ETH-Zentrum, CH-8092 Zurich,
Switzerland.
2
Professor, VAW, ETH-Zentrum, CH-8092 Zurich, Switzerland.
3
Professor, VAW, ETH-Zentrum, CH-8092 Zurich, Switzerland.
Note. Discussion open until October 1, 2005. Separate discussions
must be submitted for individual papers. To extend the closing date by
one month, a written request must be filed with the ASCE Managing
Editor. The manuscript for thispaper was submitted for review and possible publication on May 21, 2004; approved on December 9, 2004. This
paper is part of the Journal of Hydraulic Engineering, Vol. 131, No. 5,
May 1, 2005. ©ASCE, ISSN 0733-9429/2005/5-347–355/$25.00.

specifically three questions: 1 definition of jet trajectories for a
black water approach flow; 2 energy dissipation across a ski
jump; and 3 choking flow...