scholarly journals Computational Study of the Dynamics of the Taylor Bubble

Fluids ◽  
2021 ◽  
Vol 6 (11) ◽  
pp. 389
Author(s):  
Evgenii L. Sharaborin ◽  
Oleg A. Rogozin ◽  
Aslan R. Kasimov
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Bubble Surface ◽  
Vortical Structures ◽  
Azimuthal Symmetry ◽  
Open Source Framework ◽  
Theoretical Predictions ◽  
Elongated Bubble ◽  
Dynamical Features

We perform high-resolution numerical simulations of three-dimensional dynamics of an elongated bubble in a microchannel at moderate Reynolds numbers up to 1800. For this purpose, we use the coupled Brinkman penalization and volume of fluid methods implemented in the open-source framework Basilisk. The new results are validated with available experimental data and compared with previous numerical and theoretical predictions. We extend existing results to regimes with significant inertia, which are characterized by intense deformations of the bubble, including cases with azimuthal symmetry breaking. Various dynamical features are analyzed in terms of their spatiotemporal characteristics, such as frequencies and wavelengths of the bubble surface undulations and vortical structures in the flow.

scholarly journals On the formation of the counter-rotating vortex pair in transverse jets

2001 ◽  
Vol 446 ◽  
pp. 347-373 ◽  
Author(s):  
L. CORTELEZZI ◽  
A. R. KARAGOZIAN
Keyword(s):  
Flow Field ◽  
Computational Study ◽  
Near Field ◽  
Three Dimensional ◽  
Vortex Pair ◽  
Transverse Jets ◽  
Vortical Structures ◽  
Jet In Crossflow ◽  
Dynamical Generation ◽  
Counter Rotating Vortex Pair

Among the important physical phenomena associated with the jet in crossflow is the formation and evolution of vortical structures in the flow field, in particular the counter-rotating vortex pair (CVP) associated with the jet cross-section. The present computational study focuses on the mechanisms for the dynamical generation and evolution of these vortical structures. Transient numerical simulations of the flow field are performed using three-dimensional vortex elements. Vortex ring rollup, interactions, tilting, and folding are observed in the near field, consistent with the ideas described in the experimental work of Kelso, Lim & Perry (1996), for example. The time-averaged effect of these jet shear layer vortices, even over a single period of their evolution, is seen to result in initiation of the CVP. Further insight into the topology of the flow field, the formation of wake vortices, the entrainment of crossflow, and the effect of upstream boundary layer thickness is also provided in this study.

Development of a three-dimensional free shear layer

1998 ◽  
Vol 369 ◽  
pp. 49-89 ◽  
Author(s):  
A. J. RILEY ◽  
M. V. LOWSON
Keyword(s):  
Shear Layer ◽  
Flow Instability ◽  
Delta Wing ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Free Shear Layer ◽  
Velocity Data ◽  
Sweep Angle ◽  
Vortical Structures

Experiments have been undertaken to characterize the flow field over a delta wing, with an 85° sweep angle, at 12.5° incidence. Application of a laser Doppler anemometer has enabled detailed three-dimensional velocity data to be obtained within the free shear layer, revealing a system of steady co-rotating vortical structures. These sub-vortex structures are associated with low-momentum flow pockets in the separated vortex flow. The structures are found to be dependent on local Reynolds number, and undergo transition to turbulence. The structural features disappear as the sub-vortices are wrapped into the main vortex core. A local three-dimensional Kelvin–Helmholtz-type instability is suggested for the formation of these vortical structures in the free shear layer. This instability has parallels with the cross-flow instability that occurs in three-dimensional boundary layers. Velocity data at high Reynolds numbers have shown that the sub-vortical structures continue to form, consistent with flow visualization results over fighter aircraft at flight Reynolds numbers.

scholarly journals A Computational Study on Mixing of Two-Phase Flow in Microchannels

2003 ◽  
Author(s):  
Farshid Bondar ◽  
Francine Battaglia
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Mixing Index ◽  
Wave Type ◽  
Two Phase ◽  
Chaotic Flows ◽  
Two Fluids ◽  
Passive Mixing ◽  
Better Than

The passive mixing of water and alcohol, as two fluids with different densities, is carried out computationally in three-dimensional microchannels. Four designs of microchannels are considered to investigate the efficiency of mixing for Reynolds numbers ranging between 6 and 96. In a straight-type microchannel, mixing is very poor. In a square-wave-type microchannel, mixing is marginally better than the straight one. Mixing in the serpentine-type and twisted-type microchannels develops considerable better than the first two microchannels, especially at higher Reynolds numbers. However, in the twisted microchannel, the mixing index is substantially larger compared to the serpentine microchannel for the Reynolds number of 35. The higher mixing index implies the occurrence of spatially chaotic flows with a higher degree of chaos compared to the case of the serpentine microchannel. The results are compared quantitatively and qualitatively in Eulerian and Lagrangian frameworks and a correlation between Lagrangian chaos and Eulerian chaos is concluded.

The decay of a swirling perturbation of pipe Poiseuille flow

2012 ◽  
Vol 23 (3) ◽  
pp. 373-394
Author(s):  
S. A. SHEPHERD
Keyword(s):  
Poiseuille Flow ◽  
Computational Study ◽  
Three Dimensional ◽  
Circulatory System ◽  
Reynolds Numbers ◽  
Decay Rates ◽  
Secondary Flows ◽  
Polynomial Eigenvalue Problem ◽  
Vertebrobasilar Junction ◽  
The Stability

Secondary flows consisting of two pairs of vortices arise when two fluid streams meet at a confluence, such as in the airways of the human lung during expiration or at the vertebrobasilar junction in the circulatory system, where the left and right vertebral arteries converge. In this paper the decay of these secondary flows is studied by considering a four-vortex perturbation from Poiseuille flow in a straight, three-dimensional pipe. A polynomial eigenvalue problem is formulated and the exact solution for the zero Reynolds numberRis derived analytically. This solution is then extended by perturbation analysis to produce an approximation to the eigenvalues forR≪ 1. The problem is also solved numerically for 0 ≤R≤ 2,000 by a spectral method, and the stability of the computed eigenvalues is analysed using pseudospectra. For all Reynolds numbers, the decay rate of the swirling perturbation is found to be governed by complex eigenvalues, with the secondary flows decaying more slowly asRincreases. A comparison with results from an existing computational study of merging flows shows that the two models give rise to similar secondary flow decay rates.

Amplification of three-dimensional perturbations during parallel vortex–cylinder interaction

2007 ◽  
Vol 573 ◽  
pp. 457-478
Author(s):  
X. LIU ◽  
J. S. MARSHALL
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Front Surface ◽  
Inviscid Flow ◽  
Reynolds Numbers ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Features ◽  
Volume Method ◽  
Proper Orthogonal

A computational study has been performed to examine the amplification of three-dimensional flow features as a vortex with small-amplitude helical perturbations impinges on a circular cylinder whose axis is parallel to the nominal vortex axis. For sufficiently weak vortices with sufficiently small core radius in an inviscid flow, three-dimensional perturbations on the vortex core are indefinitely amplified as the vortex wraps around the cylinder front surface. The paper focuses on the effect of viscosity in regulating amplification of three-dimensional disturbances and on assessing the ability of two-dimensional computations to accurately model parallel vortex–cylinder interaction problems. The computations are performed using a multi-block structured finite-volume method for an incompressible flow, with periodic boundary conditions along the cylinder axis. Growth of three-dimensional flow features is examined using a proper-orthogonal decomposition of the Fourier-transformed vorticity field in the azimuthal and axial directions. The interaction is examined for different axial wavelengths and amplitudes of the initial helical vortex waves and for three different Reynolds numbers.

scholarly journals Energy spectrum in the dissipation range of fluid turbulence

1997 ◽  
Vol 57 (1) ◽  
pp. 195-201 ◽  
Author(s):  
D. O. MARTÍNEZ ◽  
S. CHEN ◽  
G. D. DOOLEN ◽  
R. H. KRAICHNAN ◽  
L.-P. WANG ◽  
...  
Keyword(s):  
Energy Spectrum ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Fluid Turbulence ◽  
Theoretical Predictions ◽  
Dissipation Range ◽  
Good Agreement

High-resolution, direct numerical simulations of three-dimensional incompressible Navier–Stokes equations are carried out to study the energy spectrum in the dissipation range. An energy spectrum of the form A(k/kd)α exp[−βk/kd] is confirmed. The possible values of the parameters α and β, as well as their dependence on Reynolds numbers and length scales, are investigated, showing good agreement with recent theoretical predictions. A ‘bottleneck’-type effect is reported at k/kd≈4, exhibiting a possible transition from near-dissipation to far-dissipation.

Influence of Tip Shape on Structure of Wing-Tip Vortex at Low Reynolds Numbers

2009 ◽  
Author(s):  
Djavad Kamari ◽  
Mehran Tadjfar
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Tip Vortex ◽  
Low Reynolds Numbers ◽  
Naca0012 Airfoil ◽  
Wingtip Vortex ◽  
Wing Tip Vortex ◽  
Low Reynolds ◽  
Wing Tip

An important phenomenon in three-dimensional flow over a wing is the existence of wingtip vortex. It has significant effects on the aerodynamics of flying vehicles. In this computational study, we investigate the effects of geometry of the wingtip on the structure of the wing-tip vortices. Here, we consider a rectangular half-wing with NACA0012 airfoil as cross section. The aerodynamic coefficients and the flow-field variables are computed at low Reynolds numbers below 50,000. As the edge-shape parameter is increased the wing tip vortex is weakened. This influence is higher at higher values of Reynolds number. But, the increase of angle of attack does not change the shape or rate of this increase.

Influence of Reynolds Numbers on the Flow and Heat Transfer Around Row of Magnetic Obstacles

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Xidong Zhang ◽  
Guiping Zhu ◽  
Yin Zhang ◽  
Hongyan Wang ◽  
Hulin Huang
Keyword(s):  
Heat Transfer ◽  
Vortex Shedding ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Bluff Bodies ◽  
Vortical Structures ◽  
Magnetic Vortices ◽  
Electrically Conducting ◽  
Flow And Heat Transfer ◽  
Maximum Value

An incompressible electrically conducting viscous fluid flow influenced by a local external magnetic field may develop vortical structures and eventually instabilities similar to those observed in flows around bluff bodies (such as circular cylinder), denominated magnetic obstacle. The present investigation analyzes numerically the three-dimensional flow and heat transfer around row of magnetic obstacles. The vortex structures of magnetic obstacles, heat transfer behaviors in the wake of magnetic obstacles, and flow resistance are analyzed at different Reynolds numbers. It shows that the flow behind magnetic obstacles contains four different regimes: (1) one pair of magnetic vortices, (2) three pairs namely, magnetic, connecting, and attached vortices, (3) smaller vortex shedding from the in-between magnetic obstacles, i.e., quasi-static, and (4) regular vortex shedding from the row of magnetic obstacles. Furthermore, downstream cross-stream mixing induced by the unstable wakes can enhance wall-heat transfer, and the maximum value of percentage heat transfer increment (HI) is equal to about 35%. In this case, the thermal performance factor is more than one.

Experimental Investigation of the Wake of a Discontinuous Cylinder

2010 ◽  
Author(s):  
V. S. R. Mandava ◽  
Gregory A. Kopp ◽  
Joan Herrero ◽  
Francesc Giralt
Keyword(s):  
Structural Characteristics ◽  
Dominant Role ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Near Wake ◽  
Vortical Structures ◽  
Image Velocimetry ◽  
Entrainment Process ◽  
Thin Steel Plate

The effects of a discontinuous cylinder geometry on the near wake structures was investigated experimentally. This ‘discontinuous’ circular cylinder has gaps so that solid segments 5D long are followed by gaps 2.5D long, in a repeating pattern, where D is the diameter of the cylinder. A thin steel plate was used to hold all of the cylinder pieces together. Thus, a three-dimensional (3D) wake was created at the origin with the intent to force the near wake flow to have similar structural characteristics as the far wake behind an ‘infinite/continuous’ cylinder, i.e., a near wake flow with horseshoes or double rollers formed by rapid kinking of Ka´rma´n-like vortices. Since the kinetic energy associated with the fluctuations of these near-wake 3D vortical structures is high, the flow system is considered suitable to clarify the role of these velocity patterns in the entrainment process of wake flows, which is still the subject of controversy. Particle Image Velocimetry (PIV) and Hot-Wire Anemometry (HWA) techniques were used to analyze the flow at two Reynolds numbers, Re = 10000 and 4000, in the wake of the discontinuous cylinder up to x/D = 190 downstream. The development of double rollers resulting from the interaction between the high momentum flow through the gaps and the Ka´rma´n-like vortices formed behind the solid cylindrical segments was confirmed. The Strouhal number of the double rollers in the wake is 0.14. These vortices have a dominant role in the initial wake growth. Thus, the overall flow dynamics are similar to the momentum transfer that takes place at the scale of the intermittent turbulent bulges that protrude from the wake in the far region and that were reported to be associated with double rollers.

Computational Study of Flow and Mixing Characteristics of Turbulent Opposed Jets

2013 ◽  
Author(s):  
Tarek Abdel-Salam ◽  
Srikanth B. Pidugu
Keyword(s):  
Numerical Simulations ◽  
Computational Study ◽  
Combustion Process ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Equation Model ◽  
Turbulent Shear ◽  
Jet Flows ◽  
Turbulent Shear Flow ◽  
Mixing Characteristics

The turbulent mixing of jet flows is one of the important problems of turbulent shear flow due to its application in combustion process involving fuel-oxidizer combinations such as hydrogen-air and methane-air. Fluid dynamics of opposed jets is not completely clarified as there are questions unanswered about flow stability and structure. In the present work, three-dimensional numerical simulations were conducted to study flow and mixing characteristics of turbulent opposed-jets. The numerical simulations were carried out with a finite volume CFD code. Turbulence is treated with the two equation model, the k-ε model. Nozzle diameter (d) and nozzle separation (W) are kept constant and equals to 32mm. Also, different jet velocities (Uj) have been examined corresponding to Reynolds numbers of 4500 to 12,000. Both confined and unconfined cases were simulated.

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