Efeito de escala em modelos físicos reduzidos de vertedouros em degraus

Abstract

Spillways are safety devices for dams, members of the overflow group, whose function is to discharge excess water. Due to damage observed by the flow in contact with the structure upstream of dams, in the dissipation basin, conventional chute spillways are being replaced by stepped spillways. The main interest in the usage and improvement of this structure is due to the large energy dissipation caused by the macro-roughness of the steps. The high flow speeds, along the consequent pressure drop, trigger negative pressures which favor erosion due to cavitation effects on the concrete. The present study aims to identify the scaling effect associated with the pressure loads measured in stepped spillways, through comparison of three physical models of scales 1:10, 1:15, and 1:30. The experimental methodological base used three physical models, with different reduction scales, of a hypothetical prototype with step height of 0.9m. Measurements of average and instant pressure loads were performed, through the use of piezometers and pressure transducers, inserted in the corner of the steps, on the face of the landing and the mirror. From the data collected, the behavior of the pressure loads registered along the chute were evaluated under the condition that the flow rate was equivalent between the models. The analytical methodology nondimensionalized the starting aeration position and the pressure loads along the chute, with different coefficients consolidated in the literature, so that comparison between the models was possible, as well as with other studies. The errors related to the pressure transducers were verified, as well as the frequencies of occurrence of extreme pressure load values, through non-exceedance probability curves. With the results reached in this study, it was possible to identify that there are scaling effects associated with the collected data in the models used, especially in the one with the largest scaling factor, 1:30.