PHYSICAL MODELLING AND DESIGN ESTIMATION OF INSTANTANEOUS PRESSURES IN STILLING BASINS

摘要

This paper deals on the estimation of peak values of pressure fluctuations in stilling basins, by means of systematic experimental data from laboratory tests on free hydraulic jump over an horizontal floor. This "design curves" can be applied to a particular spillway structure, which don't have all the geometric characteristics concerning the laboratory device. For this comparison the Yacyretá Dam main stilling basin, in the Paraná River, was selected. The spillway has very large specific discharge and relative small chute. In order to evaluate the degree of approximation predicted by the preliminary estimation based on pressure fluctuations on a two-dimensional free hydraulic jump on an horizontal floor related to the Yacyretá Dam stilling basin (which has spillway piers upstream, floor with a certain slope and an end sill), some statistic parameters were selected. The comparison was made for the r.m.s. amplitude of pressure fluctuations, the peak amplitudes for 0.1% and 99.9% of probability to be exceeded by more negative values and the skewness of the probability density function of pressure amplitudes. Although the differences between the basic research data and the real structure values, the proposed estimation provide useful information for the preliminary design of stilling basins. The structure must be verified by means of a Froudian hydraulic model at a generous length scale.