Abstract
ABSTRACT Stepped spillways can dissipate a great amount of energy during the flow passage over the chute, however these structures have limited operation due to the risk of cavitation damage. The induced aeration may protect the concrete chute through the air concentration near the channel bottom. Furthermore, some research studies have indicated that the presence of air in flows may reduce the mean pressures. The present research aims to analyze mean pressures, air entrainment coefficient and flow behavior over a stepped spillway with aeration induced by two different deflectors, comparing the results to natural aeration flow. Despite the jet impact influence, the induced aeration does not change significantly the mean pressures compared to natural aeration flow. The air entrainment coefficient, as well as the jet impact position, is higher for the deflector with the longer extension and, although air bubbles can be seen throughout the extension of the chute due to the air entrainment through the inferior flow surface, the induced aeration did not anticipate the boundary layer inception point position.
Highlights
Stepped spillways are structures that provide the security of the dam allowing energy dissipation, which reduces the dimensions of the downstream stilling basin
Considering the above-mentioned, the present paper aims to analyze mean pressures, the air entrainment coefficient and the flow behavior over a stepped spillway, considering aeration induced by a deflector and an air supply chamber
The mean pressures (Pm) measured at the edge of vertical (V) and horizontal (H) faces of the steps with natural aeration (NA) and induced aeration with the two deflectors tested are presented in Figure 5, considering the two extreme specific discharges tested (0.20 and 0.50 m2/s)
Summary
Stepped spillways are structures that provide the security of the dam allowing energy dissipation, which reduces the dimensions of the downstream stilling basin. Despite the advantage of energy dissipation and ease of construction of stepped spillways, these structures cannot be utilized with specific discharges over approximately 15 m2/s, according to Amador et al (2009), Gomes (2006) and Novakoski et al (2018). This limit was proposed considering the risk of the occurrence of cavitation, a phenomenon related to low pressure flows and high velocities, and which may cause serious damage to hydraulic structures. According to the authors, considering a 40 MPa concrete, 3% of air concentration is needed to eliminate cavitation damage. Some studies have demonstrated that the presence of air in the flow may increase the pressures in it, which reduces the risk of cavitation occurrence. Dong et al (2007) measured the mean pressures in a closed conduit with velocities between 20 and 50 m/s and air concentrations between 0 and 14%, concluding that the air concentration increase causes a significant elevation in the mean pressures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
