Longitudinal distribution of extreme pressures in a hydraulic jump downstream of a stepped spillway

Abstract

The overflow system of a dam safely controls the water level of a reservoir. The design of these structures should predict the damage caused by the action of the turbulent flow to which they are subject to. The combination formed by a stepped spillway followed by a stilling basin promotes a considerable portion of the energy dissipation in the actual chute of the stepped spillway but it is not sufficient to completely avoid the risk of damaging the basin. In this paper, we analyze the longitudinal distribution of extreme pressures in a stilling basin downstream of a stepped spillway. The study was based on the instant pressure data from the tests carried out in a physical model in the Laboratório de Obras Hidráulicas in IPH/UFRGS. Thus, it was found that the pressure behavior is similar to that observed in studies involving smooth chute spillways, except in the area surrounding the base of the stepped spillway, where high pressure fluctuations may occur. This happens as a result of the impact caused by the flow in the dissipation structure, which is not observed downstream of smooth chute spillways due to the existence of a vertical concordance curve between the spillway and the stilling basin.

Combination of experimental and numerical approaches to determine the main characteristics of skimming flow in stepped spillways

“…To analyze the effect of possible errors of measurement of extreme pressures commonly adopted in projects (P 0.1% and P 99.9% ), due to the uncertainties in the position of the transducer in the steps, experimental data of pressure measured with transducers by Sanagiotto & Marques (2008) were used in this study. The standard deviation values (σ d ) and statistical probability distribution coefficients N 0.1% and N 99.9% were calculated, respectively, using Equations 11 and 12, following the same methodology used in studies of extreme pressures in hydraulic jumps (Novakoski et al, 2017b;Teixeira, 2008…”

“…The physical hydraulic structure used in this work is described in Sanagiotto (2003), Sanagiotto & Marques (2008) and Gomes (2006) and is very similar to the structure used in other studies (Conterato, 2011(Conterato, , 2014Conterato et al, 2015;Novakoski et al, 2017aNovakoski et al, , 2017bOsmar et al, 2018), with small differences in the approach channel and the channel downstream of the steps.…”

Predictive Modeling the Free Hydraulic Jumps Pressure through Advanced Statistical Methods

“…The results showed that maximum pressure fluctuations were identified at the center of the vertical curve and assume values of 1% of the flow kinetic energy at the terminal tangency point of the curve. Novakoski et al [30] investigated extreme pressures with different probabilities (P* k% ) on a smooth basin downstream of a stepped spillway. The results showed that the values of P* 0.1% and P* 99.9% have lower and higher values than the values observed downstream of the smooth chute, in the region near the spillway toe, respectively.…”

A Novel Comparative Statistical and Experimental Modeling of Pressure Field in Free Jumps along the Apron of USBR Type I and II Dissipation Basins

“…Farhoudi et al [19] studied the pressure fluctuations around some chute blocks in a St. Anthony Fall (SAF) type dissipation basin. Novakoski et al [20] showed that the negative pressures in the zone near the spillway toe represent the risk of cavitation in the dissipation basin. They concluded that the extreme pressures with the probabilities of occurrence equal to 0.1% and 1% require careful assessment.…”