scholarly journals Shapes and Rise Velocities of Single Bubbles in a Confined Annular Channel: Experiments and Numerical Simulations

Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 437
Author(s):  
Andrea Cioncolini ◽  
Mirco Magnini
Keyword(s):  
Numerical Simulations ◽  
Complex Shape ◽  
Annular Channel ◽  
Qualitative Behavior ◽  
Air Bubbles ◽  
Volume Of Fluid Method ◽  
Rise Velocity ◽  
Limited Evidence ◽  
Stagnant Water ◽  
Circular Tubes

Shapes and rise velocities of single air bubbles rising through stagnant water confined inside an annular channel were investigated by means of experiments and numerical simulations. Fast video imaging and image processing were used for the experiments, whilst the numerical simulations were carried out using the volume of fluid method and the open-source package OpenFOAM. The confinement of the annular channel did not affect the qualitative behavior of the bubbles, which exhibited a wobbling rise dynamic similar to that observed in bubbles rising through unconfined liquids. The effect of the confinement on the shape and rise velocity was evident; the bubbles were less deformed and rose slower in comparison with bubbles rising through unconfined liquids. The present data and numerical simulations, as well as the data collected from the literature for use here, indicate that the size, shape, and rise velocity of single bubbles are closely linked together, and prediction methods that fail to recognize this perform poorly. This study and the limited evidence documented in the literature indicate that the confinement effects observed in non-circular channels of complex shape are more complicated than those observed with circular tubes, and much less well understood.

Numerical simulation of free ascension and coaxial coalescence of air bubbles using the volume of fluid method (VOF)

2018 ◽  
Vol 161 ◽  
pp. 47-59 ◽  
Author(s):  
W. Abbassi ◽  
S. Besbes ◽  
M. Elhajem ◽  
H. Ben Aissia ◽  
J.Y. Champagne
Keyword(s):  
Numerical Simulation ◽  
Volume Of Fluid ◽  
Air Bubbles ◽  
Volume Of Fluid Method

Design of layered structure for thermal cloak with complex shape

2016 ◽  
Vol 30 (20) ◽  
pp. 1650256 ◽  
Author(s):  
Xuebo Yuan ◽  
Guochang Lin ◽  
Youshan Wang
Keyword(s):  
Numerical Simulations ◽  
Layered Structure ◽  
Complex Shape ◽  
Thermal Protection ◽  
Design Method ◽  
Two Dimensional ◽  
Spatial Transformation ◽  
Complex Shapes ◽  
Potential Applications ◽  
Thermal Cloaking

Thermal cloaks have potential applications in thermal protection and sensing, and those cloaks with complex shapes are much more efficient in application. Layered discretization is a valid way to realize thermal cloaks designed through spatial transformation which are usually nonhomogeneous and anisotropic. However, previous studies are limited to two-dimensional cylindrical ones. Based on the theories of spatial transformation and effective medium, a four-step design method for layered structure of thermal cloak with complex shape is proposed. It is expected to realize the designed layered structure by utilizing the existing regular materials. According to the numerical simulations, the thermal cloaking performances of layered structures are good and close to that of the perfect thermal cloaks. This study has provided an effective way for realizing thermal cloak with complex shape.

scholarly journals Terminal Velocity and Drag Coefficient of Single Air Bubbles in Stagnant Water Filling in Narrow Parallel Walls.

1996 ◽  
Vol 10 (2) ◽  
pp. 146-153 ◽  
Author(s):  
Akio TOMIYAMA ◽  
Shigeo HOSOKAWA ◽  
Masahiko EBARA ◽  
Yoshiharu MIYANAGA ◽  
Yoshio KAWAKUBO ◽  
...  
Keyword(s):  
Drag Coefficient ◽  
Terminal Velocity ◽  
Air Bubbles ◽  
Stagnant Water ◽  
Water Filling

3D Direct Numerical Simulation of Air Bubbles in Water at High Reynolds Number

2002 ◽  
Author(s):  
Mario Koebe ◽  
Dieter Bothe ◽  
Jan Pruess ◽  
Hans-Joachim Warnecke
Keyword(s):  
High Reynolds Number ◽  
Terminal Velocity ◽  
Direct Numerical Simulations ◽  
Air Bubbles ◽  
Volume Of Fluid Method ◽  
Wall Distance ◽  
Starting Conditions ◽  
Shedding Frequency ◽  
High Reynolds ◽  
Good Agreement

This article presents direct numerical simulations of single air bubbles and bubble pairs in water (with log Mo = −10.6) with a highly parallelized code based on the Volume Of Fluid method (VOF). Systematical simulations of terminal velocity of single bubbles with a diameter ranging from 0.5–15 mm (ReB = 200–3750) show good agreement with experimental data from Clift et al. Bubbles with a diameter of 8 mm show strong realistic surface deformations. Initial white noise has been added to all simulations to create realistic starting conditions. Rise paths of the bubbles depend strongly on the boundary conditions and the wall distance. Small wall distances reduce the path radii of the bubbles leading to an increased wake shedding frequency. For bubble pairs with wobbling surfaces the phenomenon of shedding of vortices from the edges of the bubbles is observed.

Under the influence of crowding effects: Stability, bifurcation and chaos control for a discrete-time predator–prey model

2019 ◽  
Vol 12 (04) ◽  
pp. 1950044 ◽  
Author(s):  
Muhammad Aqib Abbasi ◽  
Qamar Din
Keyword(s):  
Steady State ◽  
Numerical Simulations ◽  
Chaos Control ◽  
Chaotic Behavior ◽  
Control Technique ◽  
Qualitative Behavior ◽  
Flip Bifurcation ◽  
Predator Prey Model ◽  
Positive Steady State ◽  
Crowding Effects

The interaction between predators and preys exhibits more complicated behavior under the influence of crowding effects. By taking into account the crowding effects, the qualitative behavior of a prey–predator model is investigated. Particularly, we examine the boundedness as well as existence and uniqueness of positive steady-state and stability analysis of the unique positive steady-state. Moreover, it is also proved that the system undergoes Hopf bifurcation and flip bifurcation with the help of bifurcation theory. Moreover, a chaos control technique is proposed for controlling chaos under the influence of bifurcations. Finally, numerical simulations are provided to illustrate the theoretical results. These results of numerical simulations demonstrate chaotic long-term behavior over a broad range of parameters. The presence of chaotic behavior in the model is confirmed by computing maximum Lyapunov exponents.

scholarly journals A coupled surface-Cahn–Hilliard bulk-diffusion system modeling lipid raft formation in cell membranes

2016 ◽  
Vol 26 (06) ◽  
pp. 1149-1189 ◽  
Author(s):  
Harald Garcke ◽  
Johannes Kampmann ◽  
Andreas Rätz ◽  
Matthias Röger
Keyword(s):  
Numerical Simulations ◽  
Lipid Raft ◽  
System Modeling ◽  
Bulk Diffusion ◽  
Lipid Phase ◽  
Qualitative Behavior ◽  
Time Behavior ◽  
Relaxation Dynamics ◽  
Unsaturated Lipids ◽  
Long Time

We propose and investigate a model for lipid raft formation and dynamics in biological membranes. The model describes the lipid composition of the membrane and an interaction with cholesterol. To account for cholesterol exchange between cytosol and cell membrane we couple a bulk-diffusion to an evolution equation on the membrane. The latter describes the relaxation dynamics for an energy which takes lipid–phase separation and lipid–cholesterol interaction energy into account. It takes the form of an (extended) Cahn–Hilliard equation. Different laws for the exchange term represent equilibrium and nonequilibrium models. We present a thermodynamic justification, analyze the respective qualitative behavior and derive asymptotic reductions of the model. In particular we present a formal asymptotic expansion near the sharp interface limit, where the membrane is separated into two pure phases of saturated and unsaturated lipids, respectively. Finally we perform numerical simulations and investigate the long-time behavior of the model and its parameter dependence. Both the mathematical analysis and the numerical simulations show the emergence of raft-like structures in the nonequilibrium case whereas in the equilibrium case only macrodomains survive in the long-time evolution.

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