Influences of Fluidic Interfaces on the Formation of Fine Scale Structure by Chaotic Mixing

1996 ◽  
Vol 118 (1) ◽  
pp. 40-47 ◽  
Author(s):  
D. F. Zhang ◽  
D. A. Zumbrunnen
Keyword(s):  
Transient Flow ◽  
Viscosity Ratio ◽  
Creeping Flow ◽  
Chaotic Mixing ◽  
Two Dimensional ◽  
Fine Scale ◽  
Flow Conditions ◽  
Computationally Efficient ◽  
Periodically Driven ◽  
Transient Flow Fields

A numerical model has been developed of two-dimensional chaotic mixing of immiscieble Newtonian fluids. A computationally efficient numerical methodology is employed which is well-suited to complex, evolving interfaces. Mixing was confined to a rectangular cavity with periodically driven upper and lower surfaces. Interfacial forces and the transient flow fields in each phase were considered to assess specifically the influences on interfacial morphology of interfacial tension and phase viscosity ratio under creeping flow conditions. Predicted morphologies are compared to those of solidified specimens synthesized by chaotic mixing in companion studies.

Effects of Junction Angle and Viscosity Ratio on Droplet Formation in Microfluidic Cross-Junction

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Ich-Long Ngo ◽  
Sang Woo Joo ◽  
Chan Byon
Keyword(s):  
Droplet Size ◽  
Viscosity Ratio ◽  
Nanoparticle Synthesis ◽  
Droplet Formation ◽  
Two Dimensional ◽  
Flow Conditions ◽  
Hydrogel Bead ◽  
Water Fraction ◽  
Side Channels ◽  
Junction Angle

This study describes the dynamic behaviors of droplet formation in microfluidic cross-junction devices (MFCDs) based on a two-dimensional numerical model using the volume of fluid (VOF) method. The effects of the junction angle (ϕ = 30 to 90 deg) between the main and side channels and the viscosity ratios (β = 10−5 to 2.0) are considered. The numerical results indicate that the active area for droplet formation in the alternating digitized pattern formation (ADPF) generally increases with the decrease of ϕ at the same water fraction (wf). A junction angle of around 60 deg was predicted as the most efficient angle at which alternating droplets are still formed at lower capillary numbers (Ca). In addition, the droplet size in ADPF decreases as ϕ increases with the same flow conditions. When ϕ is less than 90 deg and prior to approaching the equilibrium state, there always exists a periodic deviation in the relative distance between droplets. The frequency of droplet generation in ADPF decreases as ϕ decreases, and it decreases more quickly when ϕ is less than 60 deg. In addition, the throughput of MFCDs can be controlled effectively as a function of ϕ, wf, and Ca. The droplet formation in MFCDs depends significantly on the viscosity ratio β, and the ADPF becomes a jetting formation (JF) when β is greater than unity. Furthermore, the droplet size in ADPF decreases with the increase of β. The understanding of droplet formation in MFCDs is very useful for many applications, such as nanoparticle synthesis with different concentrations, hydrogel bead generation, or cell transplantation in biomedical therapy.

Stokesian motion of a spherical particle near a right corner made by tangentially moving walls

2021 ◽  
Vol 927 ◽  
Author(s):  
Francesco Romanò ◽  
Pierre-Emmanuel des Boscs ◽  
Hendrik C. Kuhlmann
Keyword(s):  
Buoyancy Force ◽  
Settling Velocity ◽  
Slow Motion ◽  
Creeping Flow ◽  
Two Dimensional ◽  
Flow Conditions ◽  
Small Particles ◽  
Gravitational Settling ◽  
Dynamical Regimes ◽  
The Impact

The slow motion of a small buoyant sphere near a right dihedral corner made by tangentially sliding walls is investigated. Under creeping-flow conditions the force and torque on the sphere can be decomposed into eleven elementary types of motion involving simple particle translations, particle rotations and wall movements. Force and torque balances are employed to find the velocity and rotation of the particle as functions of its location. Depending on the ratio of the wall velocities and the gravitational settling velocity of the sphere, different dynamical regimes are identified. In particular, a non-trivial line attractor/repeller for the particle motion exists at a location detached from both the walls. The existence, location and stability of the corresponding two-dimensional fixed point are studied depending on the wall velocities and the buoyancy force. The impact of the line attractors/repellers on the motion of small particles in cavities and its relevance for corner cleaning applications are discussed.

Modelling solid transport in building drainage systems

1996 ◽  
Vol 33 (9) ◽  
pp. 9-16 ◽  
Author(s):  
John A. Swaffield ◽  
John A. McDougall
Keyword(s):  
Decision Making ◽  
Boundary Conditions ◽  
Numerical Solution ◽  
Water Conservation ◽  
Transient Flow ◽  
Drainage System ◽  
System Model ◽  
Flow Depth ◽  
Flow Conditions ◽  
Solid Transport

The transient flow conditions within a building drainage system may be simulated by the numerical solution of the defining equations of momentum and continuity, coupled to a knowledge of the boundary conditions representing either appliances discharging to the network or particular network terminations. While the fundamental mathematics has long been available, it is the availability of fast, affordable and accessible computing that has allowed the development of the simulations presented in this paper. A drainage system model for unsteady partially filled pipeflow will be presented in this paper. The model is capable of predicting flow depth and rate, and solid velocity, throughout a complex network. The ability of such models to assist in the decision making and design processes will be shown, particularly in such areas as appliance design and water conservation.

Direct simulation of evolution and control of three-dimensional instabilities in attachment-line boundary layers

1995 ◽  
Vol 291 ◽  
pp. 369-392 ◽  
Author(s):  
Ronald D. Joslin
Keyword(s):  
Boundary Layer ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Computationally Efficient ◽  
Simulation Results ◽  
Dimensional Simulation ◽  
Attachment Line

The spatial evolution of three-dimensional disturbances in an attachment-line boundary layer is computed by direct numerical simulation of the unsteady, incompressible Navier–Stokes equations. Disturbances are introduced into the boundary layer by harmonic sources that involve unsteady suction and blowing through the wall. Various harmonic-source generators are implemented on or near the attachment line, and the disturbance evolutions are compared. Previous two-dimensional simulation results and nonparallel theory are compared with the present results. The three-dimensional simulation results for disturbances with quasi-two-dimensional features indicate growth rates of only a few percent larger than pure two-dimensional results; however, the results are close enough to enable the use of the more computationally efficient, two-dimensional approach. However, true three-dimensional disturbances are more likely in practice and are more stable than two-dimensional disturbances. Disturbances generated off (but near) the attachment line spread both away from and toward the attachment line as they evolve. The evolution pattern is comparable to wave packets in flat-plate boundary-layer flows. Suction stabilizes the quasi-two-dimensional attachment-line instabilities, and blowing destabilizes these instabilities; these results qualitatively agree with the theory. Furthermore, suction stabilizes the disturbances that develop off the attachment line. Clearly, disturbances that are generated near the attachment line can supply energy to attachment-line instabilities, but suction can be used to stabilize these instabilities.

Dynamics of a non-spherical microcapsule with incompressible interface in shear flow

2011 ◽  
Vol 678 ◽  
pp. 221-247 ◽  
Author(s):  
P. M. VLAHOVSKA ◽  
Y.-N. YOUNG ◽  
G. DANKER ◽  
C. MISBAH
Keyword(s):  
Shear Rate ◽  
Shear Flow ◽  
Viscosity Ratio ◽  
Perturbation Expansion ◽  
Shear Plane ◽  
Creeping Flow ◽  
Regular Perturbation ◽  
Cell Dynamics ◽  
Initial Shape ◽  
Flow Equations

We study the motion and deformation of a liquid capsule enclosed by a surface-incompressible membrane as a model of red blood cell dynamics in shear flow. Considering a slightly ellipsoidal initial shape, an analytical solution to the creeping-flow equations is obtained as a regular perturbation expansion in the excess area. The analysis takes into account the membrane fluidity, area-incompressibility and resistance to bending. The theory captures the observed transition from tumbling to swinging as the shear rate increases and clarifies the effect of capsule deformability. Near the transition, intermittent behaviour (swinging periodically interrupted by a tumble) is found only if the capsule deforms in the shear plane and does not undergo stretching or compression along the vorticity direction; the intermittency disappears if deformation along the vorticity direction occurs, i.e. if the capsule ‘breathes’. We report the phase diagram of capsule motions as a function of viscosity ratio, non-sphericity and dimensionless shear rate.

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