Hydraulics of skimming flows on stepped chutes: The effects of inflow conditions?

Chanson, Hubert

doi:10.1080/00221686.2006.9521660

Cited by 46 publications

(25 citation statements)

References 15 publications

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“…Rajaratnam 1990) assumed that uniform equilibrium flow conditions were achievable, Chanson's (1994aChanson's ( ,2006a observations implied some interactions between adjacent steps. Several recent studies observed a see-saw pattern in the air-water properties next to the downstream end of the chute (Chanson and Toombes 2001, Chanson and Toombes 2002a, Yasuda and Chanson 2003, Gonzalez and Chanson 2004, Felder and Chanson 2009a.…”

Section: Skimming Flowmentioning

confidence: 99%

Free-Surface Aeration, Turbulence, and Energy Dissipation on Stepped Chutes with Triangular Steps, Chamfered Steps, and Partially Blocked Step Cavities

Zhang¹

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The present thesis work contains investigations of the two-phase flow properties and energy dissipation mechanisms in a 45° steep chute lined with various types of stepped macro-roughness, including one configuration with triangular flat steps, one with chamfered steps, and three with partial step cavity blockages. The study was conducted in large-size physical models with an emphasis on the skimming flow regime subject to minimal scale effects. Detailed two-phase flow patterns were documented using an ultra-high-speed video camera and processed with advanced computer vision techniques. Both the developing clear-water flow region and the fully-developed aerated flow region were investigated.In the clear water flow region, the free-surface curvature was pronounced notably at smaller A novel setup consisting of a dual-tip phase detection probe and a total pressure transducer was proposed to enable separation of the water-phase properties from the mixture. The system allowed a better assessment of the water phase turbulence properties, which displayed similar levels of fluctuations to those in the clear water flow region. The same setup was used to appraise the energy dissipation performance of each model, with an average level of 50% energy dissipation found in all but the chamfered chute at large discharges. Direct total head measurements by the transducer appeared to be of superior quality compared to those inferred from phase-detection probe data alone, which were shown to have typically overestimated the energy dissipation potential.iii Comparison between different models revealed relatively larger sensitivities of the free-surface aeration than of the energy dissipation performance to the roughness density and the step shape.Sharp edges with a smaller roughness density appeared to improve air-entrainment, which could be linked to the state of vortex shedding determined by the roughness. The chamfered steps increased the skin friction contribution to the total drag, which was associated with a delayed onset of aeration and an energy dissipation performance that scaled poorly with an increasing discharge. Overall, the flow processes more resembled those over obstacles, which might demand investigations on an individual basis.iv Declaration by authorThis thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis.

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Section: Skimming Flowmentioning

confidence: 99%

Free-Surface Aeration, Turbulence, and Energy Dissipation on Stepped Chutes with Triangular Steps, Chamfered Steps, and Partially Blocked Step Cavities

Zhang¹

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“…where f e = Darcy friction factor estimated based upon experimental air-water flow friction factor data , Chanson 2006. If the flow does not reach normal flow conditions before the downstream end of the spillway, the flow is gradually varied downstream of the inception point of air entrainment.…”

Section: Hydraulic Design Considerationsmentioning

confidence: 99%

Embankment dam spillways and energy dissipators

Chanson¹

2013

Labyrinth and Piano Key Weirs II

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“…At the step edges, the vertical velocity distribution in the turbulent boundary layer can be approximated by a power law [8][9][10][11], and data obtained in bed-roughened flows show that there is a region above the roughness layer where the smooth boundary upstream of the steps still adequately describes the vertical velocity distribution [12][13][14]. This transition boundary layer will be used to investigate and characterize the roughness parameters and the development of turbulent boundary layer.…”

Section: Introductionmentioning

confidence: 99%

Application of Displacement Height and Surface Roughness Length to Determination Boundary Layer Development Length over Stepped Spillway

Cheng

Gulliver

Zhu

2014

Water

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Abstract:One of the most uncertain parameters in stepped spillway design is the length (from the crest) of boundary layer development. The normal velocity profiles responding to the steps as bed roughness are investigated in the developing non-aerated flow region. A detailed analysis of the logarithmic vertical velocity profiles on stepped spillways is conducted through experimental data to verify the computational code and numerical experiments to expand the data available. To determine development length, the hydraulic roughness and displacement thickness, along with the shear velocity, are needed. This includes determining displacement height d and surface roughness length z0 and the relationship of d and z0 to the step geometry. The results show that the hydraulic roughness height ks is the primary factor on which d and z0 depend. In different step height, step width, discharge and intake Froude number, the relations d/ks = 0.22-0.27, z0/ks = 0.06-0.1 and d/z0 = 2.2-4 result in a good estimate. Using the computational code and numerical experiments, air inception will occur over stepped spillway flow as long as the Bauer-defined boundary layer thickness is between 0.72 and 0.79. OPEN ACCESSWater 2014, 6 3889 Keywords: displacement height; surface roughness length; stepped spillway; boundary layer development; numerical simulations; logarithmic law; inception of air entrainment

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Hydraulics of skimming flows on stepped chutes: The effects of inflow conditions?

Cited by 46 publications

References 15 publications

Free-Surface Aeration, Turbulence, and Energy Dissipation on Stepped Chutes with Triangular Steps, Chamfered Steps, and Partially Blocked Step Cavities

Free-Surface Aeration, Turbulence, and Energy Dissipation on Stepped Chutes with Triangular Steps, Chamfered Steps, and Partially Blocked Step Cavities

Embankment dam spillways and energy dissipators

Application of Displacement Height and Surface Roughness Length to Determination Boundary Layer Development Length over Stepped Spillway

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