Self-aeration and turbulence in a stepped channel: Influence of cavity surface roughness

Takahashi, Masayuki; Gonzalez, Carlos A.; Chanson, Hubert

doi:10.1016/j.ijmultiphaseflow.2006.07.001

Cited by 24 publications

(16 citation statements)

References 11 publications

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“…6B). The trends for both flow regions were observed for all data sets in the present study and the results were consistent with results of some earlier studies (CHANSON and TOOMBES 2002, TAKAHASHI et al 2006, CHANSON and CAROSI 2007, FELDER and CHANSON 2009). …”

supporting

confidence: 93%

“…The arrangement ( Fig. 2 and 3) permitted to record the air-water flow properties within the whole cavity and it was deemed appropriate since the single-tip probe output signal is little affected by the orientation of the probe with the flow (SENE 1984, CHANSON 1988. .…”

Section: Felder S and Chanson H (2011) "Air-water Flow Propertimentioning

confidence: 99%

“…To date, in absence of prototype data, most physical measurements have been performed in laboratory with phase detection intrusive probes at step edges (MATOS et al 2000, TAKAHASHI et al 2006. There is little information on the air-water cavity flows but for the ones provided by BOES (2000), MATOS et al (2001) and GONZALEZ and CHANSON (2004) (Table 1).…”

Section: Introductionmentioning

confidence: 99%

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Air–water flow properties in step cavity down a stepped chute

Felder

Chanson

2011

International Journal of Multiphase Flow

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For the last three decades, the research into skimming flows down stepped chutes was driven by needs for better design guidelines. The skimming flow is characterised by some momentum transfer from the main stream to the recirculation zones in the shear layer developing downstream of each step edge. In the present study some physical modelling was conducted in a relatively large facility and detailed air-water flow measurements were conducted at several locations along a triangular cavity. The data implied some self-similarity of the main flow properties in the upper flow region, at step edges as well as at all locations along the step cavity. In the developing shear layer and cavity region (i.e. y/h < 0.3), the air-water flow properties presented some specific features highlighting the development of the mixing layer downstream of the step edge and the strong interactions between cavity recirculation and mainstream skimming flows. Both void fraction and bubble count rate data showed a local maximum in the developing shear layer, although the local maximum void fraction was always located below the local maximum bubble count rate. The velocity profiles had the same shape as the classical monophase flow data. The air-water flow properties highlighted some intense turbulence in the mixing layer that would be associated with large shear stresses and bubbleturbulence interactions.

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supporting

confidence: 93%

Section: Felder S and Chanson H (2011) "Air-water Flow Propertimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Air–water flow properties in step cavity down a stepped chute

Felder

Chanson

2011

International Journal of Multiphase Flow

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“…1 , Takahashi et al 2006, Meireles and Matos, 2009, Pfister and Hager 2011, Meireles et al 2012. It is often referred to as the surface inception point because it is noted as the location were aeration is first visually observed on the water surface.…”

Section: Inception Pointmentioning

confidence: 99%

Flow depth and energy coefficient relationships for stepped spillways

Hunt¹,

Kadavy²

2014

Hydraulic Structures and Society - Engineering Challenges and Extremes

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“…REMARKS Importantly, the present approach was restricted to rectangular, prismatic stepped chutes with smooth horizontal steps, constant step heights and constant bed slopes like most early studies. The effects of step roughness were recently tested (Takahashi et al 2006). The results were counter-intuitive.…”

Section: Self-similaritymentioning

confidence: 99%

Physical Modelling, Scale Effects, and Self-Similarity of Stepped Spillway Flows

Chanson

2008

World Environmental and Water Resources Congress 2008

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Stepped spillway flows are characterised by significant turbulent dissipation on the chute associated with strong free-surface aeration. Herein the validity of the Froude similitude is tested by re-analysing three experimental data sets corresponding to moderate slopes typical of embankment dams and storm waterways ( = 3.4 to 22°). The measurements included distributions of void fraction, bubble count rate, interfacial velocity, turbulence intensity, bubble chord sizes, and integral turbulent length and time scales which were scaled with a 2:1 undistorted geometric scaling ratio. The criterion selection for scale effects is a critical issue. Major differences (i.e. scale effects) were observed in terms of bubble count rates, bubble chord sizes, turbulence levels and integral turbulent length scales although little scale effects were seen in terms of void fraction and velocity distributions. The findings suggested that most physical results, including the rate of energy dissipation and re-aeration, cannot be extrapolated to prototype flow conditions without significant scale effects. A complementary approach may be based upon self-similarity, since self-similar relationships were observed systematically at both macroscopic and microscopic levels. Keywords : Stepped spillways, Air-water flow properties, Physical modelling, Scale effects, Self-similarity, Froude similitude. INTRODUCTIONStepped spillways are typically designed to increase the rate of energy dissipation on the (stepped) chute and to reduce the size of the downstream energy dissipator. At large discharges, skimming flows on stepped spillways are characterised by a significant rate of turbulent dissipation associated with strong free-surface aeration (Fig. 1). Although research in the hydraulics of stepped spillways has been very active during the last three decades (Chanson 1995,2001, Matos and Chanson 2006, the fundamental issues of dynamic similarity and scale effects were rarely discussed. How confidently can we extrapolate laboratory results to prototype spillways ? Detailed air-water flow measurements are re-analysed systematically. The data were recorded in three large-size stepped chute facilities with slopes = 3.4º, 16º and 22º, and step heights h = 0.05 m to 0.143 m. Detailed turbulence data were collected in the large-size channels with a stepped invert, including turbulence levels and turbulent time and length scales. The results are used to test the validity of the Froude similarity and to assess the scale effects and the experimental distortion to prototype stepped spillways.

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Self-aeration and turbulence in a stepped channel: Influence of cavity surface roughness

Cited by 24 publications

References 11 publications

Air–water flow properties in step cavity down a stepped chute

Air–water flow properties in step cavity down a stepped chute

Flow depth and energy coefficient relationships for stepped spillways

Physical Modelling, Scale Effects, and Self-Similarity of Stepped Spillway Flows

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