Air entrainment and safety against cavitation damage in stepped spillways over RCC dams

Matos, Jorge; Quintela, António de Carvalho; Juny, Martí Sánchez; Dolz, Josep

doi:10.1201/9781003078609-12

Cited by 10 publications

(6 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The influence of the chute angle φ was previously found by [4] and slightly lower values were obtained in the present study. The results agreed well with Cai = 0.20 found by [58,60] for φ = 53.1°.…”

Section: Reference Tests Without Aeratorsupporting

confidence: 89%

See 1 more Smart Citation

Performance and Design of a Stepped Spillway Aerator

Terrier¹,

Pfister

Schleiss

2022

Water

View full text Add to dashboard Cite

Stepped spillways are frequently limited to specific discharges under around 30 m2/s due to concerns about potential cavitation damages. A small air concentration can prevent such damages and the design of bottom aerators is well established for smooth chutes. The purpose of this study is to systematically investigate the performance of a deflector aerator at the beginning of stepped chutes. Six parameters (chute angle, step height, approach flow depth, approach flow Froude number, deflector angle and deflector height) are varied in a physical model. The spatial air concentration distribution downstream of the aerator, the cavity sub-pressure, water discharge and air discharges are measured. The results describe the commonly used air entrainment coefficient, the jet length, as well as the average and bottom air concentration development to design an aerator. The lowest bottom air concentration measured in all tests is higher than the air concentration recommended in literature to protect against cavitation damages. And, unlike smooth chutes, there appears to be no significant air detrainment downstream of the jet impact. One deflector aerator seems therefore sufficient to provide protection of a stepped spillway.

show abstract

Section: Reference Tests Without Aeratorsupporting

confidence: 89%

“…The mixture flow depth hi at the inception point showed a good agreement with literature [4,6,58,59] (Figure 3a). The two tests slightly below the general trend are the tests with Fo = 7.5 and s = 0.06 m. At this Froude number, the flow was decelerating when reaching the steps (increasing hw).…”

Section: Reference Tests Without Aeratorsupporting

confidence: 86%

Performance and Design of a Stepped Spillway Aerator

Terrier¹,

Pfister

Schleiss

2022

Water

View full text Add to dashboard Cite

show abstract

“…The pressure distributions in Figures 13 and 14 indicate that the negative pressure does not occur near the step bed, while we can see the negative pressure adjacent the vertical face of the step. All pressure results in the horizontal and vertical directions in the flat stepped spillway are similar to Matos and Quintela (2000), Chakib (2013) and Chakib and Mohammed (2015). Therefore, cavitation phenomenon is more likely to occur on the vertical face of the step.…”

Section: Tudy Of Inception Point Void Fractionmentioning

confidence: 65%

Study of inception point, void fraction and pressure over pooled stepped spillways using Flow-3D

Morovati

Eghbalzadeh

2018

Int Jnl of Num Meth for HFF

View full text Add to dashboard Cite

Purpose -While many stepped spillways geometry design guidelines were developed for flat steps, designing pooled steps might be an appropriate alternative to spillways working more efficiency. This paper aims to deal with the inception point of air-entrainment and void fraction in the different height of the pools. Following that, pressure distribution was evaluated in aerated and non-aerated regions under the effect of different heights of the pools and slopes through the use of the FLOW-3D software. Comparison of obtained numerical results with experimental ones was in good agreement for all discharges used in this study. Pools height had the insignificant effect on the inception point location. The value of void fraction was more affected in lower discharges in comparison with higher ones. Negative pressure was not seen over the crest of spillway (non-aerated region), and the maximum pressure values were obtained for pools with 15 cm height along the crest in each discharge. In all slopes, negative pressure was not formed near the step bed in the pooled and flat stepped spillways. However, negative pressure was formed in more area near the vertical face in the flat stepped spillway compared with the pooled stepped spillway which increases the probability of cavitation phenomenon in the flat stepped chute.Design/methodology/approach -A pooled stepped spillway was used in order to evaluate pressure, void fraction, and inception point. Also, different height of the pools was used. Numerical simulation of this study was fulfilled through Flow-3D software. The obtained results indicated that pools can affect two-phase flow characteristics including pressure, void fraction and inception point.Findings -Over the crest, negative pressure was not seen. Pressure values were different for all used heights and the maximum ones obtained for 15 cm height. Also, pooled stepped played a more effective role in reducing the negative pressure points compared with flat cases. Inception point location was more affected in nappe and transition flow regimes in comparison with skimming flow regime particularly for 9 and 15 cm heights.Originality/value -The research results of Felder et al. (2012a) from the University of Queensland were used to numerically simulate the flow over the pooled stepped spillway.

show abstract

“…Various formulae have been proposed for estimating the location and flow properties at the point of inception in steeply sloping stepped chutes, typical of RCC dams, as well as the main flow properties upstream and downstream of that location, such as [6,39,41,42,44,[48][49][50]. Herein, the formulae developed based on the experimental work gathered on a 1V:0.75H sloping chute [51][52][53] were adopted.…”

Section: Skimming Flow On Steep Slopes: Main Regions and Flow Propertiesmentioning

confidence: 99%

“…The mean water velocity is given as U = q/d. Air concentration close to the pseudo-bottom, downstream of the point of inception [50,51]:…”

Section: Skimming Flow On Steep Slopes: Main Regions and Flow Propertiesmentioning

confidence: 99%

Extreme Pressures and Risk of Cavitation in Steeply Sloping Stepped Spillways of Large Dams

Matos

Novakoski

Ferla

et al. 2022

Water

View full text Add to dashboard Cite

Stepped spillways have been increasingly used to handle flood releases from large dams associated with hydropower plants, and it is important to evaluate the fluctuating pressure field on the steps. Hydraulic model investigations were conducted on three 53° (1V:0.75H) sloping and relatively large-stepped chutes to characterize the mean, fluctuating, and extreme pressures acting on the most critical regions of the step faces, near their outer edges. The pressure development along the chutes is presented, generally indicating an increase of the modulus of pressure coefficients up to the vicinity of the point of inception of air entrainment, and a decrease further downstream. The extreme pressure coefficients along the spillway are fitted by an empirical formula, and the critical conditions potentially leading to cavitation on prototypes are calculated. The correlation between the cavitation index and the friction factor is also applied for predicting the onset of cavitation on prototypes, and the results are compared with the pressure data-based method. Generally, the results obtained from those methods yield typical values for the cavitation index in the vicinity of the point of inception, varying approximately from 0.8 to 0.6, respectively. In light of these results, maximum unit discharges of about 15–20 m2/s are considered advisable on 53° sloping large-stepped spillways without artificial aeration, for step heights ranging from 0.6 to 1.2 m. For much higher unit discharges, a considerable reach of the spillway may potentially be prone to the risk of cavitation damage.

show abstract

Air entrainment and safety against cavitation damage in stepped spillways over RCC dams

Cited by 10 publications

References 0 publications

Performance and Design of a Stepped Spillway Aerator

Performance and Design of a Stepped Spillway Aerator

Study of inception point, void fraction and pressure over pooled stepped spillways using Flow-3D

Extreme Pressures and Risk of Cavitation in Steeply Sloping Stepped Spillways of Large Dams

Contact Info

Product

Resources

About