Abstract
ABSTRACT The ski jump type spillway is present in large Brazilian dams. After the operation of this type of spillway, a scour hole is originated downstream of the spillway toe, complementing the energy dissipation system, because the jet is cushioned by the waterbed. As the excavation of the scour hole evolves, its shape changes, with the induction of different behaviors of the jet flow within the waterbed. The importance of this scientific study is due to the fact that scour holes downstream of ski jump spillways are in constant transformation, which can cause changes in the patterns of dynamic pressures caused on the bottom. Unexpected erosions can cause instability in the submerged slopes of the pit, jeopardizing the foundation of the dam. In this work it was proceeded physical experiments, by sectional modeling (2D), in two reduced models of 1:50 and 1:100 scales, considering two stages of erosion depths in solid bottom (fixed). It was analyzed the impact site of the jet flow on the bottom, which has the major mean dynamic pressure. As result, it was possible to identify the scale effect in the pressure coefficient between the two models tested, which allowed the adjustment of trend lines that aid to estimate the pressures that occur in prototypes, increasing safety in operation of ski jump spillways.
Highlights
The ski jump spillway (Figure 1) is a compact structure designed to release the dam overflow
The impact kinetic energy of the plunging jet against the bottom of the scour hole is measured in terms of dynamic pressure (Pd), that is, correspond
In the present work the scale effect was verified in the dynamic pressures that occur on the bottom of the scour hole, between two models in small scale, sectional (2D): a model 1:50 and another 1:100
Summary
The ski jump spillway (Figure 1) is a compact structure designed to release the dam overflow In this dissipation system, the flow digs in the river bed a scour hole, which has its shape dependent on the rock bed resistance as on the efforts caused by the jet. Marques et al (2013a) studied the distribution of the pressures due to jet impact in flat bottom geometry with the formation of a submerged hydraulic jump. In their analysis, by making comparisons with Pinto’s (1994) formula, they observed that the hydraulic parameters used to describe the pressures do not respond in the same way to these two incident jet conditions: with and without water cushion
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