A Condition for an Air Entrainment by Breaking the Surface Waves at the Free Surface

2005 ◽  
Author(s):  
Ho-Yun Nam ◽  
Jong-Man Kim ◽  
Byoung-Hae Choi ◽  
Jong-Hyeun Choi
Keyword(s):  
Free Surface ◽  
Surface Wave ◽  
Water Flow Rate ◽  
Air Entrainment ◽  
Vessel Diameter ◽  
Test Facility ◽  
Critical Conditions ◽  
Air Bubble ◽  
Water Test ◽  
Entrained Air

An experimental study has been carried out to measure the critical conditions for the inception of an air entrainment by breaking the surface wave at the free surface in the water test facility. The experimental parameters are the vessel diameter, the nozzle diameter, the mean water-level and the water flow rate. More than 400 experimental data which show whether the air is entrained or not at a given experimental condition are obtained, and an experimental correlation that describes the air entrainment condition is developed. The correlation is described by the ratio between the diameter and height of the vessel, the ratio between the diameter of the nozzle and the height of the vessel, the modified Froude number and a modified Weber number. In this experiment two cases of air entrainment are observed. One case is that the air entrainment occurred due to the destruction of the surface wave from the center, and the other case is due to the crash of the water wave to the vessel wall. Theses two cases occur irregularly and the entrained air bubble distributes uniformly in the water.

Effect of Entrained Air on Cavitation Damage

1974 ◽  
Vol 1 (1) ◽  
pp. 97-107 ◽  
Author(s):  
S. O. Russell ◽  
G. J. Sheehan
Keyword(s):  
High Velocity ◽  
Additional Data ◽  
Air Entrainment ◽  
Test Facility ◽  
Hydraulic Structures ◽  
Cavitation Damage ◽  
Water Flows ◽  
Velocity Flow ◽  
High Head ◽  
Entrained Air

When water flows at high velocity over a surface, quite small boundary irregularities may trigger cavitation which can, in turn, cause extensive damage. Concrete surfaces downstream from high head outlet gates are particularly vulnerable to cavitation damage.Operating experience and previous experimental work suggest that cavitation damage can be greatly reduced and, in some cases, eliminated by entrained air in the water.Experiments were carried out with a special high head test facility in Vancouver to obtain additional data on the effect of air entrainment. These tests confirmed its effectiveness. In this paper, previous evidence is reviewed, the experiments are described, and the results presented. Finally suggestions are made about the design of hydraulic structures which involve high velocity flow.

Hydraulic design of intake structures of deeply located underground tunnel systems

1999 ◽  
Vol 39 (9) ◽  
pp. 137-144 ◽  
Author(s):  
K. Toda ◽  
K. Inoue
Keyword(s):  
Free Surface ◽  
Energy Dissipation ◽  
Vortex Flow ◽  
Air Entrainment ◽  
Swirling Flows ◽  
Underground Storage ◽  
Hydraulic Design ◽  
Literature Reviews ◽  
Entrained Air ◽  
Air Control

This paper deals with hydraulic effects of intake structures of underground storage or tunnel systems from the aspect of energy dissipation and entrained air control. First, through the literature reviews, the advantage of vortex-flow dropshaft type is confirmed. Next, with the analytical solutions of free-surface swirling flows in vertical dropshaft, the energy dissipation effects of vortex-flow dropshaft are examined and some results of practical use are obtained. Also, the relation between the dropshaft shape and air entrainment is studied and the excellent of the helicoidal-ramp dropshaft is clarified. Based on the above results, the directions of the hydraulic designs of drop structures are proposed.

A RELAP5/MOD3 Model for the Estimation of Air Pull-Through for a Draining Tank

2004 ◽  
Author(s):  
D. S. Lucas ◽  
R. Riemke
Keyword(s):  
Air Entrainment ◽  
Air Bubble ◽  
Vortex Model ◽  
Pull Through ◽  
Entrained Air

An air pull-through vortex model was implemented in RELAP5/MOD3 to investigate air-entrainment from a draining tank. Surge tanks covered by an air bubble are vulnerable to the entrainment of air into the liquid. If such a system is connected to a pump the possibility of entrained air from draining resulting in cavitation and pump degradation is possible.

scholarly journals Experimental Investigations of Free-Surface Aeration in the Developing Flow of Two-Dimensional Water Jets

1998 ◽  
Vol 120 (4) ◽  
pp. 738-744 ◽  
Author(s):  
T. Brattberg ◽  
H. Chanson ◽  
L. Toombes
Keyword(s):  
Free Surface ◽  
Flow Region ◽  
Air Entrainment ◽  
Experimental Investigations ◽  
Two Dimensional ◽  
Air Bubble ◽  
Surface Aeration ◽  
Water Jets ◽  
Developing Flow ◽  
Air Diffusion

Turbulent water jets discharging into the atmosphere are often characterized by a substantial amount of free-surface aeration. The effects can be detrimental or beneficial. In any case, the knowledge of the air entrainment mechanisms is essential for an optimum design. New experimental data are presented in the developing flow region of two-dimensional water jets discharging into air. The results indicate that the air diffusion takes place rapidly downstream of the nozzle and it is nearly independent of the momentum transfer process. Further, the distribution of air bubble frequency may be related to the air content distribution by a parabolic relationship.

Competition of roller rotation and horizontal crossflow to control the free surface cusp-induced air entrainment

2021 ◽  
Vol 33 (11) ◽  
pp. 112114
Author(s):  
Santosh Kumar Panda ◽  
Basanta Kumar Rana ◽  
Parmod Kumar
Keyword(s):  
Free Surface ◽  
Air Entrainment

Large amplitude progressive interfacial waves

1979 ◽  
Vol 93 (3) ◽  
pp. 433-448 ◽  
Author(s):  
Judith Y. Holyer
Keyword(s):  
Free Surface ◽  
Surface Wave ◽  
Surface Waves ◽  
Large Amplitude ◽  
Phase Speed ◽  
Maximum Height ◽  
Interfacial Waves ◽  
Free Surface Waves ◽  
Lower Fluid ◽  
Over The Top

This paper contains a study of large amplitude, progressive interfacial waves moving between two infinite fluids of different densities. The highest wave has been calculated using the criterion that it has zero horizontal fluid velocity at the interface in a frame moving at the phase speed of the waves. For free surface waves this criterion is identical to the criterion due to Stokes, namely that there is a stagnation point at the crest of each wave. I t is found that as the density of the upper fluid increases relative to the density of the lower fluid the maximum height of the wave, for fixed wavelength, increases. The maximum height of a Boussinesq wave, which has the density almost the same above and below the interface, is 2·5 times the maximum height of a surface wave of the same wavelength. A wave with air over the top of it can be about 2% higher than the highest free surface wave. The point at which the limiting criterion is first satisfied moves from the crest for free surface waves to the point half-way between the crest and the trough for Boussinesq waves. The phase speed, momentum, energy and other wave properties are calculated for waves up to the highest using Padé approximants. For free surface waves and waves with air above the interface the maximum value of these properties occurs for waves which are lower than the highest. For Boussinesq waves and waves with the density of the upper fluid onetenth of the density of the lower fluid these properties each increase monotonically with the wave height.

scholarly journals Reoxidation Processes Prediction in Gating System by Numerical Simulation for Aluminium Alloys

2017 ◽  
Vol 17 (3) ◽  
pp. 23-26 ◽  
Author(s):  
M. Brůna ◽  
D. Bolibruchová ◽  
R. Pastirčák
Keyword(s):  
Free Surface ◽  
Aluminium Alloys ◽  
Oxide Films ◽  
Front Tracking ◽  
Gating System ◽  
Liquid Aluminium ◽  
Surface Time ◽  
Filling Pattern ◽  
Entrained Air ◽  
Flow Experiments

Abstract Pouring of liquid aluminium is typically accompanied by disturbance of the free surface. During these disturbances, the free surface oxide films can be entrained in the bulk of liquid, also pockets of air can be accidentally trapped in this oxide films. The resultant scattering of porosity in castings seems nearly always to originate from the pockets of entrained air in oxide films. Latest version of ProCast software allows to identify the amount of oxides formed at the free surface and where they are most likely to end-up in casts. During a filling calculation, ProCast can calculate different indicators which allow to better quantify the filling pattern. The fluid front tracking indicator “Free surface time exposure” has the units [cm2*s]. At each point of the free surface, the free surface area is multiplied by the time. This value is cumulated with the value of the previous timestep. In addition, this value is transported with the free surface and with the fluid flow. Experiments to validate this new functions were executed.

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.

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