scholarly journals Air–Water Properties in Rectangular Free-Falling Jets

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1593
Author(s):  
José M. Carrillo ◽  
Patricio R. Ortega ◽  
Luis G. Castillo ◽  
Juan T. García
Keyword(s):  
Water Flow ◽  
Inner Core ◽  
Current Knowledge ◽  
Air Entrainment ◽  
Lateral Spread ◽  
Phase Detection ◽  
Flow Properties ◽  
Entire Cross Section ◽  
Water Properties ◽  
Free Falling

This study analyzes the air–water flow properties in overflow nappe jets. Data were measured in several cross-sections of rectangular free-falling jets downstream of a sharp-crested weir, with a maximum fall distance of 2.0 m. The flow properties were obtained using a conductivity phase-detection probe. Furthermore, a back-flushing Pitot-Prandtl probe was used in order to obtain the velocity profiles. Five specific flows rates were analyzed, from 0.024 to 0.096 m3/s/m. The measurements of the air–water flow allowed us to characterize the increment of the air entrainment during the fall, affecting the flow characteristic distributions, reducing the non-aerated water inner core, and increasing the lateral spread, thereby leading to changes in the jet thickness. The results showed slight differences between the upper and lower nappe trajectories. The experimental data of the jet thickness related to a local void fraction of 50% seemed to be similar to the jet thickness due only to gravitational effects until the break-up length was reached. The amount of energy tended to remain constant until the falling distance was over 15 times greater than the total energy head over the weir crest, a distance at which the entrained air affected the entire cross-section, and the non-aerated core tended to disappear. The new experiments related with air–water properties in free-falling jets allow us to improve the current knowledge of turbulent rectangular jets.

scholarly journals Experimental Characterization of Air Entrainment in Rectangular Free Falling Jets

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1773
Author(s):  
José M. Carrillo ◽  
Patricio R. Ortega ◽  
Luis G. Castillo ◽  
Juan T. García
Keyword(s):  
Phase Change ◽  
Water Flow ◽  
Void Fraction ◽  
Cross Sections ◽  
Scale Effects ◽  
Air Entrainment ◽  
Phase Detection ◽  
Detection Probe ◽  
Relative Differences ◽  
Free Falling

This experimental study presents an analysis of the air–water flow in rectangular free-falling jets. The measurements were obtained downstream of a 1.05 m wide sharp-crested weir. The properties of the air–water flow were registered in several cross-sections of the nappe. A conductivity phase detection probe was employed, sampling at 20 kHz. Three different specific flows were considered, with energy head over the crest of 0.080, 0.109 and 0.131 m to avoid scale effects. To analyze the flow properties, air–water parameters during the fall, such as the phase change spatial distribution, air–water phase change of frequency, Sauter mean diameter, bubble chord length, turbulent intensities and spectral analyses, were studied. The jet thickness behaviors (inner jet core and free surface) were also analyzed in the falling jet. The jet thickness related to a void fraction of 90% seems to be similar to the theoretical proposal obtained by Castillo et al. (2015), while the jet thickness related to a void fraction of 10% seems to be similar to the jet thickness due to gravitational effects. The results show relative differences in the behavior of the upper and lower sides of the nappe. The experimental data allow us to improve on and complement previous research.

scholarly journals Experimental investigations of air entrainment in transition and skimming flows down a stepped chute

2002 ◽  
Vol 29 (1) ◽  
pp. 145-156 ◽  
Author(s):  
H Chanson ◽  
L Toombes
Keyword(s):  
Free Surface ◽  
Water Flow ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Transition Flow ◽  
Flow Properties ◽  
Flow Measurements ◽  
Surface Aeration ◽  
Stepped Chute ◽  
Uniform Equilibrium

Stepped spillways have been used for about 3500 years. The last few decades have seen the development of new construction materials, design techniques, and applications, for example, embankment overtopping protection systems. Although it is commonly acknowledged that free-surface aeration is significant in stepped chutes, experimental data are scarce, often limited to very steep slopes (α ~ 50°). This paper presents an experimental study conducted in a large-size stepped chute (α = 22°, h = 0.1 m, W = 1 m). Observations demonstrate the existence of a transition flow pattern for intermediate flow rates between nappe and skimming flows. Detailed air–water flow measurements were conducted in both transition and skimming flows, immediately downstream of the inception point of free-surface aeration where uniform equilibrium flow conditions were not achieved. In skimming flows, a complete characterization is developed for the distributions of void fraction, bubble count rate, and velocity, and flow resistance data are compared with other studies. Transition flows exhibit significantly different air–water flow properties. They are highly aerated, requiring the design of comparatively high chute sidewalls.Key words: stepped spillway, air entrainment, two-phase flow properties, skimming flow, transition flow.

scholarly journals Turbulence characteristics in skimming flows on stepped spillways

2008 ◽  
Vol 35 (9) ◽  
pp. 865-880 ◽  
Author(s):  
G. Carosi ◽  
H. Chanson
Keyword(s):  
Energy Dissipation ◽  
Water Flow ◽  
Time Scales ◽  
Bubbly Flow ◽  
Stepped Spillway ◽  
Phase Detection ◽  
Flow Properties ◽  
Flow Measurements ◽  
Stepped Spillways ◽  
Turbulent Characteristics

The stepped spillway design is characterized by an increase in the rate of energy dissipation on the chute associated with a reduction of the size of the downstream energy dissipation system. This study presents a thorough investigation of the air–water flow properties in skimming flows with a focus on the turbulent characteristics. New measurements were conducted in a large-size facility (θ = 22°; step height, h = 0.1 m) with several phase-detection intrusive probes. Correlation analyses were applied to estimate the integral turbulent length and time scales. The skimming flow properties presented some basic characteristics that were qualitatively and quantitatively in agreement with previous air–water flow measurements in skimming flows. Present measurements showed some relatively good correlation between turbulence intensities T u and turbulent length and time scales. These measurements also illustrated large turbulence levels and large turbulent time and length scales in the intermediate region between the spray and bubbly flow regions.

scholarly journals Modeling of Kinetics of Air Entrainment in Water Produced by Vertically Falling Water Flow

2014 ◽  
Vol 20 (3) ◽  
Author(s):  
Adelė VAIDELIENĖ ◽  
Arvaidas GALDIKAS ◽  
Paulius TERVYDIS
Keyword(s):  
Water Flow ◽  
Air Entrainment ◽  
Kinetics Of

Flow over a stepped chute with and without macro-roughness elements

2004 ◽  
Vol 31 (5) ◽  
pp. 880-891 ◽  
Author(s):  
Mehmet Ali Kökpinar
Keyword(s):  
Water Flow ◽  
High Speed ◽  
Length Distribution ◽  
Air Entrainment ◽  
Air Concentration ◽  
Bubble Frequency ◽  
Two Phase ◽  
Air Bubble ◽  
Roughness Elements ◽  
Stepped Chute

High-speed two-phase flows over a 30° stepped flume were experimentally investigated using macro-roughness elements. The roughness elements included combinations of steps and horizontal strips. Local values of air concentration, air bubble frequency, and mean chord lengths were measured by a fiber-optical instrumentation system in the air–water flow region. The range of unit discharge of water was varied from 0.06 to 0.20 m2/s. Three step configurations were studied: (i) without macro-roughness elements, (ii) with macro-roughness elements on each step, and (iii) with macro-roughness elements on each second step (AMR configuration). The results were compared in terms of onset flow conditions and internal air–water flow parameters such as local air concentration, mean air bubble chord length distribution, and air bubble frequency in the skimming flow regime. It was observed that the AMR configuration produced the maximum free-surface aeration among the other configurations. This alternative step geometry has potential for less cavitation damage than conventional step geometry because of the greater air entrainment.Key words: stepped chute, air-entrainment, air-water flow properties, macro-roughness elements, skimming flow.

On the applicability of Washburn law: study of mercury and water flow properties in cement-based materials

2004 ◽  
Vol 37 (2) ◽  
pp. 107-113 ◽  
Author(s):  
A. Aït-Mokhtar ◽  
O. Amiri ◽  
P. Dumargue ◽  
A. Bouguerra
Keyword(s):  
Water Flow ◽  
Flow Properties ◽  
Cement Based Materials
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