Interaction between free-surface aeration and total pressure on a stepped chute

Zhang, Gangfu; Chanson, Hubert

doi:10.1016/j.expthermflusci.2015.12.011

Cited by 16 publications

(4 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Equation (3) predicts a quasi-parabolic relationship between bubble frequency and mean void fraction across the gas-liquid column, thus a pseudo linear relation between the root mean square of the instantaneous void fraction and the bubble frequency. An extended solution yields a relationship between bubble frequency and interfacial turbulence intensity (Zhang and Chanson 2016).…”

Section: Basic Considerations On Gas-liquid Structurementioning

confidence: 99%

On void fraction and flow fragmentation in two-phase gas-liquid free-surface flows

Zhang

Chanson

2019

Mechanics Research Communications

Self Cite

View full text Add to dashboard Cite

In free-surface flows, the interactions between high-velocity liquid and atmosphere may lead to strong gas-liquid mixing and complex multiphase flow interactions. In this study, the void fraction power spectrum density (PSD) is used to provide an alternative view of the airwater flow composition. The high frequency range of the PSD curve reflects contributions of small chord times, while the low frequency range contains contributions of both small and large chord times. Likewise, the interactions between the smallest bubbles contribute approximately uniformly to the entire frequency range of the spectrum, while any interaction involving large bubbles/drops will be modulated by 1/f 2. It is shown that the void fraction spectra are a powerful tool in providing an alternative view of the air-water flow composition.

show abstract

Section: Basic Considerations On Gas-liquid Structurementioning

confidence: 99%

On void fraction and flow fragmentation in two-phase gas-liquid free-surface flows

Zhang

Chanson

2019

Mechanics Research Communications

Self Cite

View full text Add to dashboard Cite

show abstract

“…The crest was made of smooth, painted marine ply. The discharge was deduced from integration of velocity profiles measured on the crest (Zhang and Chanson 2016b ).…”

Section: Inflow Conditionsmentioning

confidence: 99%

Air-water flow properties in stepped chutes with modified step and cavity geometries

Zhang

Chanson

2018

International Journal of Multiphase Flow

Self Cite

View full text Add to dashboard Cite

Skimming air-water flow properties were investigated in a stepped chute configured with triangular steps, chamfered steps, and partially blocked step cavities. The turbulent interactions between air and water were examined using a synchronised system consisting of a dual-tip phase-detection probe and a pressure transducer mounted side-by-side. In comparison to uniform triangular steps, the chamfered steps were found to cause a reduction in air entrainment and an increase in mean velocity gradient next to the pseudo-bottom. Partial cavity blockages appeared to have little effect on air entrainment, but were linked to an increased presence of large-scale structures in the overflow, which likely resulted from a reduction in mutual sheltering between adjacent step elements. The results indicated that modifications of step and cavity geometries might have significant implications on stepped chute design.

show abstract

“…The signal was amplified and low-pass filtered at a cut off frequency of 2 kHz before digitisation by a NI DAQ (NI USB-6251 BNC) acquisition system. A sampling frequency of 5 kHz was selected to minimise information loss (Wang et al 2014, Zhang et al 2016b). The sampling parameters used for the total pressure transducer are summarised in Table 2.3.…”

Section: Inflow Conditionsmentioning

confidence: 99%

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

Zhang¹

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Interaction between free-surface aeration and total pressure on a stepped chute

Cited by 16 publications

References 40 publications

On void fraction and flow fragmentation in two-phase gas-liquid free-surface flows

On void fraction and flow fragmentation in two-phase gas-liquid free-surface flows

Air-water flow properties in stepped chutes with modified step and cavity geometries

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

Contact Info

Product

Resources

About