Abstract
ABSTRACT The operation of stepped spillways is limited by a range of discharges due to the risk of occurrence of the cavitation phenomenon and erosion on its steps. Since there is a demand for spillways with the possibility of overflow of greater discharges, the designs seek to increase the air concentration of the flow, which can occur through the installation of piers in the spillway in order to protect the structure from the above mentioned damage. The aim of this work is to analyze flow characteristics and extreme minimum and maximum pressures with non-exceedance probability of 0.1% and 99.9% acting next to the step edges of the spillway with aeration induced by piers through an experimental analysis in a physical model. Based on the results obtained, flow behavior was defined and equations for predicting the extreme pressures that occur along the stepped spillway with aeration induced by piers were proposed.
Highlights
Stepped spillways are characterized by the significant energy dissipation that occurs during the passage of the flow through the chute due to the macroroughness imposed by the steps
For the induced aeration, the specific flow exerts less influence on the PSAP, i.e. the PSAP remains practically constant with the increase of the specific flow, oscillating between the longitudinal positions 1.80 and 1.90 m. These results indicate that the lower air incorporation affected the behavior of the superficial aeration, since the PSAP has occurred on the second step from the deflector, regardless of the unit discharge tested, which makes PSAP occur in a practically constant longitudinal position
Based on the evaluation of the flow behavior characteristics of the physical model of a stepped spillway, it has been found that flow with induced aeration differs from the behavior of the natural aeration
Summary
Stepped spillways are characterized by the significant energy dissipation that occurs during the passage of the flow through the chute due to the macroroughness imposed by the steps. As the unit discharge increases, the inception point of natural aeration moves downstream, exposing a larger region of the structure to such risks. Several studies on stepped spillways were developed to understand the flow behavior and hydrodynamic efforts that occur along the stepped chute, such as the studies published by Povh et al (2004), Sánchez-Juny et al (2007, 2008), Arantes et al (2009), Takahashi & Ohtsu (2012), Conterato et al (2015), Estrella et al (2015), Xu et al (2015), Dai Prá et al (2016), Zhang & Chanson (2016, 2017, 2018), Osmar et al (2018) and Nóbrega et al (2020). Based on the knowledge of hydrodynamic pressures on the steps, studies found the implementation of stepped spillways to be limited to a range of discharges due to the risk of cavitation damage
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