NUMERICAL INVESTIGATION OF THE INTERACTION MECHANISM OF TWO BUBBLES

2010 ◽  
Vol 21 (01) ◽  
pp. 33-49 ◽  
Author(s):  
HAN WANG ◽  
ZHEN-YU ZHANG ◽  
YONG-MING YANG ◽  
HUI-SHENG ZHANG
Keyword(s):  
Numerical Experiments ◽  
Bubble Radius ◽  
Interaction Mechanism ◽  
Incompressible Fluids ◽  
Liquid Jet ◽  
Liquid Region ◽  
Liquid Density ◽  
Large Pressure ◽  
Large Pressure Gradient ◽  
Two Bubbles

In the frame of inviscid and incompressible fluids without taking into consideration of surface tension effects, the axisymmetric evolution of two buoyancy-driven bubbles in an infinite and initially stationary liquid are investigated numerically by VOF method. The numerical experiments are performed for two bubbles with same size, with the following one being half of the leading one, and with the leading one being half of the following one, and for different bubble distances. The ratio of gas density to liquid density is 0.001. It is found by numerical experiment that when the distance between the two bubbles is greater than or equal to one and half of the bigger bubble radius, the interaction is very weak and the two bubbles evolute like isolated ones rising in an infinite liquid. When the two bubbles come closer, the leading bubble itself evolutes like an isolated one rising in an infinite liquid. However, due to the smaller distance between the two bubbles, large pressure gradient forms in the liquid region near the top of the following bubble, which causes the upward stretch of its top part no matter what sizes of the two bubbles are. When the distance between the two bubbles is less than or equal to three-tenth of the bigger bubble radius, before the liquid jet behind the leading bubble fully developed, the top part of the following bubble has already been sucked into the leading one, giving a pear-like shape. Soon after the following bubble merges with the leading one. It is also found that for the smaller bubble, its transition to toroidal is always faster than that of the bigger one because of its smaller size. The mechanism of the above phenomena has been analyzed numerically.

Isothermal Bubble Motion Through a Rotating Liquid

1972 ◽  
Vol 94 (1) ◽  
pp. 187-192 ◽  
Author(s):  
D. L. Schrage ◽  
H. C. Perkins
Keyword(s):  
Radial Direction ◽  
Terminal Velocity ◽  
Distilled Water ◽  
Analytical Prediction ◽  
Bubble Motion ◽  
Large Pressure ◽  
Rotating Liquid ◽  
Angular Velocities ◽  
Large Pressure Gradient ◽  
Good Agreement

An analytical and experimental study of isothermal bubble motion through a liguid which is itself in motion is presented. Both analytical and experimental results are reported for the velocities and trajectories of oxygen bubbles moving through a liquid annulus which is rotating at angular velocities ranging from 500 to 1500 rpm. Results are presented for both distilled water and glycerin. The analytical prediction of the trajectories and velocities showed good agreement with the experimental data. It was found that the bubbles, which were injected at the exterior of the liquid annulus, spiralled inward rapidly and, due to the large pressure gradient in the radial direction, did not reach a constant or terminal velocity.

scholarly journals Estimation of High-Speed Liquid-Jet Velocity Using a Pyro Jet Injector

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Naohisa Takagaki ◽  
Toru Kitaguchi ◽  
Masashi Iwayama ◽  
Atsushi Shinoda ◽  
Hiroshige Kumamaru ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
High Speed ◽  
Liquid Jet ◽  
Liquid Density ◽  
Liquid Viscosity ◽  
Ejection Velocity ◽  
Piston Motion ◽  
Ansys Fluent ◽  
Piston Displacement ◽  
Jet Velocity

AbstractThe high-speed liquid-jet velocity achieved using an injector strongly depends on the piston motion, physical property of the liquid, and container shape of the injector. Herein, we investigate the liquid ejection mechanism and a technique for estimating the ejection velocity of a high-speed liquid jet using a pyro jet injector (PJI). We apply a two-dimensional numerical simulation with an axisymmetric approximation using the commercial software ANSYS/FLUENT. To gather the input data applied during the numerical simulation, the piston motion is captured with a high-speed CMOS camera, and the velocity of the piston is measured using motion tracking software. To reproduce the piston motion during the numerical simulation, the boundary-fitted coordinates and a moving boundary method are employed. In addition, we propose a fluid dynamic model (FDM) for estimating the high-speed liquid-jet ejection velocity based on the piston velocity. Using the FDM, we consider the liquid density variation but neglect the effects of the liquid viscosity on the liquid ejection. Our results indicate that the liquid-jet ejection velocity estimated by the FDM corresponds to that predicted by ANSYS/FLUENT for several different ignition-powder weights. This clearly shows that a high-speed liquid-jet ejection velocity can be estimated using the presented FDM when considering the variation in liquid density but neglecting the liquid viscosity. In addition, some characteristics of the presented PJI are observed, namely, (1) a very rapid piston displacement within 0.1 ms after a powder explosion, (2) piston vibration only when a large amount of powder is used, and (3) a pulse jet flow with a temporal pulse width of 0.1 ms.

scholarly journals Barycentric Rational Collocation Method for the Incompressible Forchheimer Flow in Porous Media

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Qingli Zhao ◽  
Yongling Cheng
Keyword(s):  
Porous Media ◽  
Numerical Analysis ◽  
Collocation Method ◽  
Numerical Stability ◽  
Numerical Experiments ◽  
Convergence Rates ◽  
Incompressible Fluids ◽  
Flow In Porous Media ◽  
The Matrix ◽  
Forchheimer Flow

Barycentric rational collocation method is introduced to solve the Forchheimer law modeling incompressible fluids in porous media. The unknown velocity and pressure are approximated by the barycentric rational function. The main advantages of this method are high precision and efficiency. At the same time, the algorithm and program can be expanded to other problems. The numerical stability can be guaranteed. The matrix form of the collocation method is obtained from the discrete numerical schemes. Numerical analysis and error estimates for velocity and pressure are established. Numerical experiments are carried out to validate the convergence rates and show the efficiency.

Small Scale Flow Structure Evolution During Mechanical Heart Valve Closure

2013 ◽  
Author(s):  
J. Mousel ◽  
H. S. Udaykumar ◽  
K. B. Chandran
Keyword(s):  
Heart Valves ◽  
Thrombus Formation ◽  
Mechanical Heart Valve ◽  
Structure Evolution ◽  
Small Scale ◽  
Leakage Flows ◽  
Large Pressure ◽  
Large Pressure Gradient ◽  
Valve Position ◽  
Systolic Phase

Despite half a century of use, mechanical heart valves still require further research to reduce the non-physiologic nature of the flow field, which is the source of potential medical complications, of which the most serious complication is thrombus formation [1]. In the systolic phase of the flow, excessive fluid stresses are generated by the non-physiologic flow patterns [2, 3]. In the closed valve position, a large pressure gradient is imposed across the device which leads to the generation of strong and damaging small-scale leakage flows that entrain platelets such that they are exposed to elevated stresses for excessive time durations [4–6].

The Fluid Mechanics of Membrane Filtration

2007 ◽  
Author(s):  
Jack S. Hale ◽  
Alison Harris ◽  
Qilin Li ◽  
Brent C. Houchens
Keyword(s):  
Membrane Filtration ◽  
Concentration Polarization ◽  
Membrane Surface ◽  
Convective Transport ◽  
Contaminated Water ◽  
Permeate Flux ◽  
Large Pressure ◽  
Cake Layer ◽  
Large Pressure Gradient ◽  
Concentration Polarization Layer

Reverse osmosis and nanofiltration membranes remove colloids, macromolecules, salts, bacteria and even some viruses from water. In crossflow filtration, contaminated water is driven parallel to the membrane, and clean permeate passes through. A large pressure gradient exists across the membrane, with permeate flow rates two to three orders of magnitude smaller than that of the crossflow. Membrane filtration is hindered by two mechanisms, concentration polarization and caking. During filtration, the concentration of rejected particles increases near the membrane surface, forming a concentration polarization layer. Both diffusive and convective transport drive particles back into the bulk flow. However, the increase of the apparent viscosity in the concentration polarization layer hinders diffusion of particles back into the bulk and results in a small reduction in permeate flux. Depending on the number and type of particles present in the contaminated water, the concentration polarization will either reach a quasi-steady state or particles will begin to deposit onto the membrane. In the later case, a cake layer eventually forms on the membrane, significantly reducing the permeate flux. Contradictive theories suggest that the cake layer is either a porous solid or a very viscous (yield stress) fluid. New and refined models that shed light on these theories are presented.

scholarly journals Interaction between two spherical bubbles rising in a viscous liquid

2011 ◽  
Vol 673 ◽  
pp. 406-431 ◽  
Author(s):  
YANNICK HALLEZ ◽  
DOMINIQUE LEGENDRE
Keyword(s):  
Stokes Equations ◽  
Bubble Diameter ◽  
Bubble Radius ◽  
Three Dimensional ◽  
Potential Effect ◽  
Navier Stokes ◽  
General Description ◽  
Wake Effect ◽  
Spherical Bubbles ◽  
Two Bubbles

The three-dimensional flow around two spherical bubbles moving in a viscous fluid is studied numerically by solving the full Navier–Stokes equations. The study considers the interaction between two bubbles for moderate Reynolds numbers (50 ≤ Re ≤ 500, Re being based on the bubble diameter) and for positions described by the separation S (2.5 ≤ S ≤ 10, S being the distance between the bubble centres normalised by the bubble radius) and the angle θ (0° ≤ θ ≤ 90°) formed between the centreline and the direction perpendicular to the direction of the motion. We provide a general description of the interaction extending the results obtained for two bubbles moving side by side (θ = 0°) by Legendre, Magnaudet & Mougin (J. Fluid Mech., vol. 497, 2003, p. 133) and for two bubbles moving in line (θ = 90°) by Yuan & Prosperetti J. Fluid Mech., vol. 278, 1994, p. 325). Simple models based on physical arguments are given for the drag and lift forces experienced by each bubble. The interaction is the combination of three effects: a potential effect, a viscous correction (Moore's correction) and a significant wake effect observed on both the drag and the transverse forces of the second bubble when located in the wake of the first one.

The generation and collapse of a foam layer at the roof of a basaltic magma chamber

1989 ◽  
Vol 203 ◽  
pp. 347-380 ◽  
Author(s):  
Claude Jaupart ◽  
Sylvie Vergniolle
Keyword(s):  
Surface Tension ◽  
Volume Fraction ◽  
Bubble Radius ◽  
Critical Value ◽  
Simple Theory ◽  
Liquid Density ◽  
Foam Layer ◽  
Gas Flux ◽  
Basaltic Volcanoes ◽  
Foam Thickness

Basaltic volcanoes erupt in several different regimes which have not been explained. At Kilauea (Hawaii), eruption can take the form of either fire fountaining, where gas-rich jets propel lava clots to great heights in the atmosphere, or quiet effusive outflow of vesicular lava. Another regime is commonly observed at Stromboli, where large gas slugs burst intermittently at the vent. In an attempt to provide a unifying framework for these regimes, we investigate phenomena induced by degassing in a reservoir which empties into a small conduit. Laboratory experiments are done in a cylindrical tank topped by a thin vertical tube. Working liquids are silicone oils and glycerol solutions to investigate a range of viscosity and surface tension. Gas bubbles are generated at the tank bottom with known bubble diameter and total gas flux. The bubbles rise through the tank and accumulate in a foam layer at the roof. Depending on the behaviour of this foam layer, three different regimes can be distinguished: (i) steady horizontal flow of the foam leading to bubbly flow in the conduit; (ii) alternating regimes of foam build-up and collapse leading to the eruption of a single, large gas pocket; (iii) flow of the foam partially coalesced into larger gas pockets leading to intermittent slug flow in the conduit. These regimes have natural counterparts in basaltic volcanoes.A simple theory is proposed to explain regimes (i) and (ii). The bubbles in contact with the roof deform under the action of buoyancy forces, developing flat contact areas whose size increases as a function of foam thickness. Maximum deformation corresponds to a critical thickness hc = 2σ/ερlgR, where σ is the coefficient of surface tension, ρl the liquid density, g the acceleration due to gravity, R the bubble radius and ε the gas volume fraction in the foam. The foam thickness is determined by a balance between the input of bubbles from below and the output into the conduit, and is proportional to (μlQ/ε2 ρlg)¼, where μl is the liquid viscosity and Q the gas flux. A necessary and sufficient condition for collapse is that it exceeds the critical value hc. In a liquid of given physical properties, this occurs when the gas flux exceeds a critical value which depends on viscosity, surface tension and bubble size. Experimental determinations of the critical gas flux and of the time between two events of foam collapse are in agreement with this simple theory.

Pesticide Accidents in Relation to Weather Conditions

1980 ◽  
Vol 7 (3) ◽  
pp. 219-222
Author(s):  
Don Fred ◽  
Edwin Kessler
Keyword(s):  
Wind Speed ◽  
Pressure Gradient ◽  
Strong Relationship ◽  
Weather Conditions ◽  
Strong Positive Correlation ◽  
Slight Tendency ◽  
Positive Correlation ◽  
Large Pressure ◽  
Large Pressure Gradient ◽  
Weak Wind

Research has shown that it is inadvisable to spray crops during either near-absolute calms or very windy conditions; therefore, we studied weather maps and reports of herbicide accidents to investigate the hypothesis that the strong positive correlation between largescale pressure gradient and wind-speed can be used to facilitate prediction of favourable spraying times in Oklahoma. We gave detailed study to the conditions of 10 May 1977, the date in that year when the most herbicide accidents were reported. Although a relatively large pressure gradient existed, there was only weak wind at the KTVY meteorologically instrumented tower (150 km distant from the area of the accidents). We also searched for a strong relationship between herbicide accidents and the pressure gradient through tabulations of daily gradients and accident reports. Only a slight tendency is shown for accidents to occur on days with larger gradients. Research and significant findings for this study were hampered by a lack of specificity and detail in accident reports.

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