Flow Characteristics of Skimming Flows in Stepped Channels

Ohtsu, Iwao; Yasuda, Youichi; Takahashi, Masayuki

doi:10.1061/(asce)0733-9429(2004)130:9(860)

Cited by 161 publications

(94 citation statements)

References 13 publications

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“…The findings were comparable to a number of earlier studies (Chanson 1995, Ohtsu et al 2004, Felder and Chanson 2009a. Some similar flow regimes were observed on the pooled stepped spillway (Fig.…”

Section: Flow Patternssupporting

confidence: 91%

“…A number of embankment dam stepped spillways were built with a range of design and construction techniques, including gabions, Reno mattresses, reinforced earth, pre-cast concrete slabs and roller compacted concrete (RCC) (Chanson 1995). The stepped profile allows an increased rate of energy dissipation on the spillway chute , Ohtsu et al 2004) and the design engineers must assess accurately the turbulent kinetic energy dissipation down the staircase chute, in particular for the large discharges per unit width corresponding to the skimming flow regime. A characteristic feature of skimming flows is the high level of turbulence and free-surface aeration (Rajaratnam 1990, Peyras et al 1992, Chanson 1994.…”

Section: Introductionmentioning

confidence: 99%

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Flow aeration, cavity processes and energy dissipation on flat and pooled stepped spillways for embankments

2013

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The design floods of several reservoirs were recently re-evaluated and the revised spillway outflow could result in dam overtopping with catastrophic consequences for some embankment structures. Herein a physical study was performed on flat and pooled stepped spillways with a slope typical of embankments ( = 26.6°) and four stepped configurations: a stepped spillway with flat horizontal steps, a pooled stepped spillway, and two stepped spillways with in-line and staggered configurations of flat and pooled steps. The focus of the study was on the flow aeration, air-water flow properties, cavity flow processes, and energy dissipation performances. The results demonstrated the strong aeration of the flow for all configurations. On the in-line and staggered configurations of flat and pooled steps, the flow was highly three-dimensional. The residual head and energy dissipation rates at the stepped chute downstream end were calculated based upon the detailed air-water flow properties. The results showed that the residual energy was the lowest for the flat stepped weir. The data for the stepped spillway configuration with in-line and staggered configurations of flat and pooled steps showed large differences in terms of residual head in the transverse direction. Altogether the present results showed that, on a 26.6 slope stepped chute, the designs with in-line and staggered configurations of flat and pooled steps did not provide any advantageous performances in terms of energy dissipation and flow aeration, but they were affected by three-dimensional patterns leading to some flow concentration.

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Section: Flow Patternssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Flow aeration, cavity processes and energy dissipation on flat and pooled stepped spillways for embankments

2013

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“…For a chute slope of θ ¼ 21.8°(1V∶2.5H), the residual head was smallest within the range 14°≤ θ ≤ 26.6°, suggesting an optimum embankment dam design for this slope. These observations were consistent with the observations of Ohtsu et al (2004) and Gonzalez and Chanson (2006). • The discussers questioned if the distance between the inception point of air entrainment and the downstream end of the spillway was long enough to be in the uniform (equilibrium) flow region.…”

supporting

confidence: 79%

Closure to “Simple Design Criterion for Residual Energy on Embankment Dam Stepped Spillways” by Stefan Felder and Hubert Chanson

Felder

Chanson

2017

J. Hydraul. Eng.

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“…In the last two decades, extensive experimental research has been developed to characterize the flow on conventional stepped spillways for chute slopes typical of either embankment or concrete dams downstream of the inception point of air entrainment, including the assessment of variables such as air concentration and velocity distribution [4,9,24,26,37,42,57,63,67,71] or the pressure field on the steps [2,4,41,74,85]. Empirical models have been developed for predicting the main air-water flow properties along the chute by Hager and Boes [45], Matos [57], Chanson [25], Boes and Hager [9,10], Meireles [65], Renna [71] and Ohtsu et al [67].…”

Section: Introductionmentioning

confidence: 99%

Laboratory measurements and multi-block numerical simulations of the mean flow and turbulence in the non-aerated skimming flow region of steep stepped spillways

2010

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We present and discuss the results of a comprehensive study addressing the non-aerated region of the skimming flow in steep stepped spillways. Although flows in stepped spillways are usually characterized by high air concentrations concomitant with high rates of energy dissipation, the non-aerated region becomes important in small dams and/or spillways with high specific discharges. A relatively large physical model of such spillway was used to acquire data on flow velocities and water levels and, then, well-resolved numerical simulations were performed with a commercial code to reproduce those experimental conditions. The numerical runs benefited from the ability of using multi-block grids in a Cartesian coordinate system, from capturing the free surface with the TruVOF method embedded in the code, and from the use of two turbulence models: the k−ε and the RNG k−ε models. Numerical results are in good agreement with the experimental data corresponding to three volumetric flow rates in terms of the time-averaged velocities measured at diverse steps in the spillway, and they are in very satisfactory agreement for water levels along the spillway. In addition, the numerical results provide information on the turbulence statistics of the flow. This work also discusses important aspects of the flow, such as the values of the exponents of the power-law velocity profiles, and the characteristics of the development of the boundary layer in the spillway.

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Flow Characteristics of Skimming Flows in Stepped Channels

Cited by 161 publications

References 13 publications

Flow aeration, cavity processes and energy dissipation on flat and pooled stepped spillways for embankments

Flow aeration, cavity processes and energy dissipation on flat and pooled stepped spillways for embankments

Closure to “Simple Design Criterion for Residual Energy on Embankment Dam Stepped Spillways” by Stefan Felder and Hubert Chanson

Laboratory measurements and multi-block numerical simulations of the mean flow and turbulence in the non-aerated skimming flow region of steep stepped spillways

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