Numerical Simulation of Ski-Jump Hydraulic Behavior

The hydraulic behavior of ski jumps is investigated numerically using the OpenFOAM digital library. A number of ski-jump cases has been simulated by following the RANS approach (Reynolds Averaged Navier-Stokes equations), using the k-ω SST closure model, and the VoF technique (Volume of Fluid) for the tracking of the free surface. Particular attention is given to the pressure distributions in the zone of impact of the falling jet, and to the length of the jet itself, as defined as the distance along the x-direction between the point of maximum dynamic pressure head, and the origin of the reference frame. A chart is proposed reporting the correlation line (and correspondent formal expression) between the approach Froude numbers and the lengths of the jets, in the limit of other parameters tested. The chart may serve as a useful tool for the determination of the length of the jet taking off from the bucket, starting from the value of the approach Froude number.

The hydraulics of ski jumps is an issue of great importance in dam construction, the former being in practice the only existing solution as related to the dissipation of energy from high-speed spillway ows from large dams. Inspite of the fact that thousands of dams have been built all over the world in the years, and besides the reporting of specic case studies, the general hydraulic behavior of the ski jumps has been scarcely investigated. In the present work, the hydraulic behavior of ski jumps is investigated numerically using the OpenFOAM digital library [1]. A number of skijump cases has been simulated numerically following the RANS (Reynolds Averaged Navier-Stokes equations) approach, using the kappa-omega SST closure model [2] and ther VoF technique (Volume of Fluid) for the tracking of the ow free surface [3]. The numerical procedure appears to be a rather favourable option to overcome the complexities always associated to experimental measurements. Particular attention is given to the forces, to the pressure distribution in the zone of impact of the falling jet, and to the length of the jet itself. The issue of the length of the falling jet is particularly considered, as dened as the distance along the x- direction between the point of maximum dynamic pressure head in the zone of impact of the jet along the centerline of the tailwater channel, and the origin of the reference system. A chart is proposed, reporting the correlation lines (and correspondent formal expressions) between the approach Froude numbers and the lengths of the jets, in the limit of the range of other parameters tested. The chart may serve as a useful tool to determine the length of the jet taking o from the bucket, starting from the value of the approach Froude number.