Artificial aeration of stepped spillways by crest piers and flares for the mitigation of cavitation damage

Koen, Jaco; Bosman, D.E.; Basson, G. R.

doi:10.17159/2309-8775/2019/v61n2a3

Cited by 9 publications

(10 citation statements)

References 8 publications

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“…The growth in concentration is due to the early onset of air entrainment into the flow by the standing wave and the longitudinal vortices generated by the crest pier. This phenomenon has also been observed for stepped spillways [40,41]. The graphs indicate that bottom air concentration varied in a continuous fashion along the spillway length.…”

Section: Resultssupporting

confidence: 71%

“…From the present investigation and the studies presented by Calitz [40] and Koen [41], it can be stated that crest piers can help in either eliminating or reducing the risk of cavitation damage in smooth and steeped spillways. The crest piers induce artificial aeration by the formation of longitudinal vortex, standing and shock waves that introduce a greater percentage of air on the spillway bottom, when compared to the spillway without pier.…”

Section: Resultssupporting

confidence: 58%

“…Nowadays, aerators are extensively used in spillways all around the world to prevent cavitation damage. In the same way, more recently, between 2015 and 2017, Calitz [40] and Koen [41] studied the artificial aeration on stepped spillways by using various crest pier designs. They found that the bullnose pier practically eliminated the risk of cavitation damage, allowing increasing the unit discharge capacity.…”

Section: Introductionmentioning

confidence: 98%

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Experimental Investigation of Artificial Aeration on a Smooth Spillway with a Crest Pier

Luna-Bahena

Pozos‐Estrada

Ortiz-Martínez

et al. 2018

Water

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Crest piers placed on overflow spillways induce standing waves at the downstream end of them and the supercritical flow expands after flowing past the rear of the pier. The expanding flow from each side of a pier will intersect and form disturbances or shock waves that travel laterally as they move downstream and eventually reach the chute sidewalls. Recently, investigations regarding crest piers are related with artificial aeration on stepped spillways to eliminate the risk of cavitation damage. However, there is a lack of studies on standing and shock waves in smooth spillways concerning the air entrainment into the flow in presence of crest piers. This paper presents the study of the combined effect on air entrainment of a crest pier and an aerator on the bottom of a smooth spillway (configuration 1). For comparison, experimental tests were developed in the spillway without pier, that is in presence of aerator only (configuration 2). The configuration 1 results show that the air concentration distribution on the spillway bottom across the width and length of the chute increases in comparison with configuration 2, reducing even more the risk of cavitation damage and enhancing the safety of the hydraulic structure.

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Section: Resultssupporting

confidence: 71%

Section: Resultssupporting

confidence: 58%

Section: Introductionmentioning

confidence: 98%

See 1 more Smart Citation

Experimental Investigation of Artificial Aeration on a Smooth Spillway with a Crest Pier

Luna-Bahena

Pozos‐Estrada

Ortiz-Martínez

et al. 2018

Water

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“…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, 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.…”

Section: Introductionmentioning

confidence: 99%

Influence of aeration induced by piers on the starting position of the flow aeration and extreme pressures in stepped spillways

Priebe

Ferla

Novakoski

et al. 2021

RBRH

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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.

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“…This phenomenon has been described before by Moñino [9] and Kramer [10]. Moreover, several studies have analyzed the effect of emulsionated flows in spillways with artificial aeration, as in Luna-Bahena [11] and Koen [12]. There are different proposals for energy dissipation mechanisms in open channel flows, depending on the regime analyzed.…”

Section: Introductionmentioning

confidence: 72%

Experimental Analysis of the Influence of Aeration in the Energy Dissipation of Supercritical Channel Flows

Rebollo

López

Garrote

et al. 2019

Water

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Energy dissipation structures play an important role in flood risk management. Many variables need to be considered for the design of these structures. Aeration has been one of the more studied phenomena over the last years, due to its influence in the performance of hydraulic structures. The purpose of the work presented in this article is to experimentally characterize the effects of aeration on boundary friction in supercritical and fully turbulent flows. The physical model used to analyze the aeration effects consists of a spillway chute 6.5 m high and a stilling basin of 10 m length and 2 m high. A pump and compressor supply the water-air mixture and are controlled at the entrance by valves and flowmeters. The ensuing channel is monitored to determine the velocity profile and air concentration of the flow into the stilling basin. The average values of both variables and Manning’s coefficient along the channel are used to determine the relation between air concentration and energy dissipation by friction. A velocity increase with greater air entrainment has been found in all scenarios since friction is the main energy dissipation mechanism in open channels flow. Finally, an equation is proposed to characterize this evolution based on the results obtained.

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Artificial aeration of stepped spillways by crest piers and flares for the mitigation of cavitation damage

Cited by 9 publications

References 8 publications

Experimental Investigation of Artificial Aeration on a Smooth Spillway with a Crest Pier

Experimental Investigation of Artificial Aeration on a Smooth Spillway with a Crest Pier

Influence of aeration induced by piers on the starting position of the flow aeration and extreme pressures in stepped spillways

Experimental Analysis of the Influence of Aeration in the Energy Dissipation of Supercritical Channel Flows

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