Development of the interfacial air layer in the non-aerated region of high-velocity spillway flows. Instabilities growth, entrapped air and influence on the self-aeration onset

Valero, Daniel; Bung, Daniel B.

doi:10.1016/j.ijmultiphaseflow.2016.04.012

Cited by 52 publications

(30 citation statements)

References 54 publications

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“…where σaw is the surface tension between air and water, r1 and r2 are the two principle radii of curvatures of the free-surface deformation, and Ad is the surface deformation area. Valero and Bung (2016) extended this formulation by including stresses in the air superlayer flow. They also noted that by including the effects induced by an air superlayer the triggering velocity for viscous KelvinHelmholtz instability is substantially reduced.…”

Section: Free-surface Aerationmentioning

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: Free-surface Aerationmentioning

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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“…Waves have been also observed in the non-aerated region of spillway flows (Anwar 1994, Felder and Chanson 2014, Valero and Bung 2015, Zhang and Chanson 2016. Valero and Bung (2015) observed the dynamics of these waves in the inception point location and Valero and Bung (2016) described the different types of waves, pointing out the role of air-water friction in the wave generation when high velocity flows take place. Another clear evidence of free-surface turbulencedue to the underlying hydrodynamic processes -can be observed in hydraulic jumps (Chanson and Brattberg 2000), which have been also investigated previously using ultrasonic sensors (Chachereau andChanson 2011, Wang andChanson 2015a).…”

Section: Introductionmentioning

confidence: 99%

“…Naturally, sensors interference can also happen between ultrasonic sensors and temperature effect must be contemplated, but non-intrusiveness can represent an advantage. Main benefits of other techniques can be met by ultrasonic sensors, but its performance has to be carefully assessed to ensure reliable non-intrusive measurements of free-surface profiles, free-surface fluctuations, free-surface correlation time scales, free-surface wave celerity and frequencies (Murzyn and Chanson 2009, Chachereau and Chanson 2011, Bung 2013, Felder and Chanson 2014, Valero and Bung 2016. Additionally, how the footprint relates to the measurement has not been still assessed.…”

Section: Introductionmentioning

confidence: 99%

On the estimation of free-surface turbulence using ultrasonic sensors

Zhang

Valero

Bung

et al. 2018

Flow Measurement and Instrumentation

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Accurate determination of free-surface dynamics has attracted much research attention during the past decade and has important applications in many environmental and water related areas. In this study, the free-surface dynamics in several turbulent flows commonly found in nature were investigated using a synchronised setup consisting of an ultrasonic sensor and a high-speed video camera. Basic sensor capabilities were examined in dry conditions to allow for a better characterisation of the present sensor model. The ultrasonic sensor was found to adequately reproduce free-surface dynamics up to the second order, especially in two-dimensional scenarios with the most energetic modes in the low frequency range. The sensor frequency response was satisfactory in the sub-20 Hz band, and its signal quality may be further improved by low-pass filtering prior to digitisation. The application of the USS to characterise entrapped air in high-velocity flows is also discussed.

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“…Experimental data on air concentrations and different semi-empirical relations can be found in Wang Inlet boundary layers (water and air): the supercritical flow impacting the hydraulic jump develops from farther upstream as long as its extension allows. Two boundary layers take place, the water boundary layer that can affect the hydraulic jump characteristics [44,70]-and thus it is common to distinguish between partially developed and fully developed inlet flows-and the interfacial air layer flow [72], which could affect the hydraulic jump air entrained quantities according to Ervine [71]. For the supercritical water boundary layer development, several methods exist, such as Castro-Orgaz and Hager [73] and Castro-Orgaz [74] based on spillway prototype scale velocity profiles.…”

mentioning

confidence: 99%

“…For the supercritical water boundary layer development, several methods exist, such as Castro-Orgaz and Hager [73] and Castro-Orgaz [74] based on spillway prototype scale velocity profiles. For the interfacial air flow, the only data-set was collected by Valero and Bung [72], which also discussed on the occurring free surface instabilities in supercritical flows that were suggested by Ervine [71] to affect the entrained quantities. A general framework for the computation of the free surface perturbations can be found in Valero and Bung [75].…”

mentioning

confidence: 99%

Numerical Simulation of Hydraulic Jumps. Part 1: Experimental Data for Modelling Performance Assessment

Valero

Viti

Gualtieri

2018

Water

Self Cite

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Hydraulic jumps have been the object of extensive experimental investigation, providing the numerical community with a complete case study for models’ performance assessment. This study constitutes an exhaustive literature review on hydraulic jumps’ experimental datasets. Both mean and turbulent parameters characterising hydraulic jumps are comprehensively discussed, presenting at least a reference to one dataset. Three studies stand out over other datasets due to their completeness. Using them as reference for model validation may ensure homogeneous and comparable performance assessment for the upcoming numerical models. Experimental inaccuracies are also addressed, allowing the numerical modeller to understand the uncertainties of reduced physical models and its limitations. Part 2 presents the three-dimensional numerical investigations to date and their main achievements.

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Development of the interfacial air layer in the non-aerated region of high-velocity spillway flows. Instabilities growth, entrapped air and influence on the self-aeration onset

Cited by 52 publications

References 54 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

On the estimation of free-surface turbulence using ultrasonic sensors

Numerical Simulation of Hydraulic Jumps. Part 1: Experimental Data for Modelling Performance Assessment

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