Direct Numerical Simulation of Air Bubbles in Water/Glycerol Mixtures: Shapes and Velocity Fields

2003 ◽  
Author(s):  
Mario Koebe ◽  
Dieter Bothe ◽  
Hans-Joachim Warnecke
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Density Ratio ◽  
Quantitative Agreement ◽  
Velocity Fields ◽  
Creeping Flow ◽  
Computational Domain ◽  
Kolmogorov Length Scale ◽  
Aspect Ratios ◽  
Approximate Analytical Solutions

In this paper results of direct numerical simulation (DNS) of bubbles rising in viscous Newtonian liquids with high-density ratio are presented. The simulations are carried out with the highly parallelized code FS3D, which employs the Volume-of-Fluid (VOF) method. The high degree of parallization of the code allows high resolution of the computational domain, such that the Kolmogorov length scale inside the liquid phase is resolved for the simulations. For validation of the numerical results the terminal rise velocities, bubble shapes and flow fields are compared to experimental data as well as to approximate analytical solutions. For high Morton numbers terminal rise velocities and aspect ratios agree very well with experimental values. For lower Morton numbers there is an increasing difference between experimental and numerical rise velocities. The aspect ratios of ellipsoidal bubbles match both with experimental measurements and with theoretical values of Taylor and Acrivos. At very low Reynolds numbers (ReB < 1) the velocity fields in and outside of the bubble show good semi-quantitative agreement with the analytical creeping flow solution of Hadamard and Rybczynski.

scholarly journals Direct Numerical Simulation of Pore-Scale Trapping Events During Capillary-Dominated Two-Phase Flow in Porous Media

2021 ◽  
Author(s):  
Mosayeb Shams ◽  
Kamaljit Singh ◽  
Branko Bijeljic ◽  
Martin J. Blunt
Keyword(s):  
Numerical Simulation ◽  
Porous Media ◽  
Direct Numerical Simulation ◽  
Complex Geometry ◽  
Flow In Porous Media ◽  
Pore Scale ◽  
Contact Lines ◽  
Two Phase ◽  
X Ray ◽  
Aspect Ratios

AbstractThis study focuses on direct numerical simulation of imbibition, displacement of the non-wetting phase by the wetting phase, through water-wet carbonate rocks. We simulate multiphase flow in a limestone and compare our results with high-resolution synchrotron X-ray images of displacement previously published in the literature by Singh et al. (Sci Rep 7:5192, 2017). We use the results to interpret the observed displacement events that cannot be described using conventional metrics such as pore-to-throat aspect ratio. We show that the complex geometry of porous media can dictate a curvature balance that prevents snap-off from happening in spite of favourable large aspect ratios. We also show that pinned fluid-fluid-solid contact lines can lead to snap-off of small ganglia on pore walls; we propose that this pinning is caused by sub-resolution roughness on scales of less than a micron. Our numerical results show that even in water-wet porous media, we need to allow pinned contacts in place to reproduce experimental results.

scholarly journals Direct numerical simulation and large-eddy simulation of stationary buoyancy-driven turbulence

2009 ◽  
Vol 643 ◽  
pp. 279-308 ◽  
Author(s):  
D. CHUNG ◽  
D. I. PULLIN
Keyword(s):  
Numerical Simulation ◽  
Large Eddy Simulation ◽  
Direct Numerical Simulation ◽  
Density Ratio ◽  
Stationary Flow ◽  
Small Scale ◽  
Scalar Flux ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Active Scalar

We report direct numerical simulation (DNS) and large-eddy simulation (LES) of statistically stationary buoyancy-driven turbulent mixing of an active scalar. We use an adaptation of the fringe-region technique, which continually supplies the flow with unmixed fluids at two opposite faces of a triply periodic domain in the presence of gravity, effectively maintaining an unstably stratified, but statistically stationary flow. We also develop a new method to solve the governing equations, based on the Helmholtz–Hodge decomposition, that guarantees discrete mass conservation regardless of iteration errors. Whilst some statistics were found to be sensitive to the computational box size, we show, from inner-scaled planar spectra, that the small scales exhibit similarity independent of Reynolds number, density ratio and aspect ratio. We also perform LES of the present flow using the stretched-vortex subgrid-scale (SGS) model. The utility of an SGS scalar flux closure for passive scalars is demonstrated in the present active-scalar, stably stratified flow setting. The multi-scale character of the stretched-vortex SGS model is shown to enable extension of some second-order statistics to subgrid scales. Comparisons with DNS velocity spectra and velocity-density cospectra show that both the resolved-scale and SGS-extended components of the LES spectra accurately capture important features of the DNS spectra, including small-scale anisotropy and the shape of the viscous roll-off.

Direct numerical simulation of free falling sphere in creeping flow

2010 ◽  
Vol 24 (3-4) ◽  
pp. 109-120 ◽  
Author(s):  
Rupesh K. Reddy ◽  
Shi Jin ◽  
K. Nandakumar ◽  
Peter D. Minev ◽  
Jyeshtharaj B. Joshi
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Creeping Flow ◽  
Falling Sphere ◽  
Free Falling

Direct numerical simulation of a separated turbulent boundary layer

1998 ◽  
Vol 374 ◽  
pp. 379-405 ◽  
Author(s):  
Y. NA ◽  
P. MOIN
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Shear Stress ◽  
Turbulent Boundary Layer ◽  
Direct Numerical Simulation ◽  
Shear Layer ◽  
Stokes Equations ◽  
Pressure Fluctuations ◽  
Shear Stresses ◽  
Computational Domain

A separated turbulent boundary layer over a flat plate was investigated by direct numerical simulation of the incompressible Navier–Stokes equations. A suction-blowing velocity distribution was prescribed along the upper boundary of the computational domain to create an adverse-to-favourable pressure gradient that produces a closed separation bubble. The Reynolds number based on inlet free-stream velocity and momentum thickness is 300. Neither instantaneous detachment nor reattachment points are fixed in space but fluctuate significantly. The mean detachment and reattachment locations determined by three different definitions, i.e. (i) location of 50% forward flow fraction, (ii) mean dividing streamline (ψ=0), (iii) location of zero wall-shear stress (τw=0), are in good agreement. Instantaneous vorticity contours show that the turbulent structures emanating upstream of separation move upwards into the shear layer in the detachment region and then turn around the bubble. The locations of the maximum turbulence intensities as well as Reynolds shear stress occur in the middle of the shear layer. In the detached flow region, Reynolds shear stresses and their gradients are large away from the wall and thus the largest pressure fluctuations are in the middle of the shear layer. Iso-surfaces of negative pressure fluctuations which correspond to the core region of the vortices show that large-scale structures grow in the shear layer and agglomerate. They then impinge on the wall and subsequently convect downstream. The characteristic Strouhal number St=fδ*in/U0 associated with this motion ranges from 0.0025 to 0.01. The kinetic energy budget in the detachment region is very similar to that of a plane mixing layer.

Direct Numerical Simulation of Mass Transfer from Spherical Bubbles: the Effect of Interface Contamination at Low Reynolds Numbers

2006 ◽  
Vol 4 (1) ◽  
Author(s):  
Adil Dani ◽  
Arnaud Cockx ◽  
Pascal Guiraud
Keyword(s):  
Numerical Simulation ◽  
Mass Transfer ◽  
Direct Numerical Simulation ◽  
Reynolds Numbers ◽  
Solid Sphere ◽  
Creeping Flow ◽  
Spherical Bubbles ◽  
Cap Model ◽  
Liquid Mass Transfer ◽  
Low Reynolds

The gas-liquid mass transfer from bubbles is estimated by Direct Numerical Simulation for fully contaminated bubbles behaving as solid spheres, partially contaminated spherical bubbles and clean spherical bubbles. Partial contamination of bubble interface is accounted by the Stagnant Cap Model to show the effect of the surfactant on hydrodynamic and mass transfer at low Reynolds number. Hydrodynamics results are validated by comparison with other works of the literature. The numerical mass transfer is then analysed in term of local and averaged Sherwood numbers. The comparison of DNS results with classical relations gives the good scaling of Sherwood with Pe1/3 and Pe1/2 respectively for solid sphere and clean bubble in creeping flow. For partially contaminated bubble and after validation of simulated drag coefficient, the effect of the contamination on mass transfer is shown for several Peclet numbers. A correlation for Sherwood number in function of contamination angle is then proposed in creeping flow.

Direct Numerical Simulation of an Open-Cell Metallic Foam through Lattice Boltzmann Method

2015 ◽  
Vol 18 (3) ◽  
pp. 707-722 ◽  
Author(s):  
Daniele Chiappini ◽  
Gino Bella ◽  
Alessio Festuccia ◽  
Alessandro Simoncini
Keyword(s):  
Numerical Simulation ◽  
Porous Media ◽  
Direct Numerical Simulation ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Media Analysis ◽  
Metallic Foam ◽  
Computational Domain ◽  
Open Cell ◽  
Boltzmann Method

AbstractIn this paper Lattice Boltzmann Method (LBM) has been used in order to perform Direct Numerical Simulation (DNS) for porous media analysis. Among the different configurations of porous media, open cell metallic foams are gaining a key role for a large number of applications, like heat exchangers for high performance cars or aeronautic components as well. Their structure allows improving heat transfer process with fruitful advantages for packaging issues and size reduction. In order to better understand metallic foam capabilities, a random sphere generation code has been implemented and fluid-dynamic simulations have been carried out by means of a kinetic approach. After having defined a computational domain the Reynolds number influence has been studied with the aim of characterizing both pressure drop and friction factor throughout a finite foam volume. In order to validate the proposed model, a comparison analysis with experimental data has been carried out too.

scholarly journals Direct Numerical Simulation of Turbulent Flows Laden with Droplets or Bubbles

2019 ◽  
Vol 51 (1) ◽  
pp. 217-244 ◽  
Author(s):  
Said Elghobashi
Keyword(s):  
Numerical Simulation ◽  
Numerical Methods ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Surface Deformation ◽  
Direct Numerical Simulations ◽  
Solid Particles ◽  
Length Scale ◽  
Single Droplet ◽  
Kolmogorov Length Scale

This review focuses on direct numerical simulations (DNS) of turbulent flows laden with droplets or bubbles. DNS of these flows are more challenging than those of flows laden with solid particles due to the surface deformation in the former. The numerical methods discussed are classified by whether the initial diameter of the bubble/droplet is smaller or larger than the Kolmogorov length scale and whether the instantaneous surface deformation is fully resolved or obtained via a phenomenological model. Also discussed are numerical methods that account for the breakup of a single droplet or bubble, as well as multiple droplets or bubbles in canonical turbulent flows.

Instability waves in a low-Reynolds-number planar jet investigated with hybrid simulation combining particle tracking velocimetry and direct numerical simulation

2010 ◽  
Vol 655 ◽  
pp. 344-379 ◽  
Author(s):  
TAKAO SUZUKI ◽  
HUI JI ◽  
FUJIO YAMAMOTO
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Particle Tracking ◽  
Particle Tracking Velocimetry ◽  
Hybrid Simulation ◽  
Velocity Fields ◽  
Computational Time ◽  
Spatial Problem ◽  
Instability Waves ◽  
Planar Jet

Instability waves in a laminar planar jet are extracted using hybrid unsteady-flow simulation combining particle tracking velocimetry (PTV) and direct numerical simulation (DNS). Unsteady velocity fields on a laser sheet in a water tunnel are measured with time-resolved PTV; subsequently, PTV velocity fields are rectified in a least squares sense so that the equation of continuity is satisfied, and they are transplanted to a two-dimensional incompressible Navier–Stokes solver by setting a multiple of the computational time step equal to the frame rate of the PTV system. As a result, the unsteady hybrid velocity field approaches that of the measured one over time, and we can simultaneously acquire the unsteady pressure field. The resultant set of flow quantities satisfies the governing equations, and their resolution is comparable to that of numerical simulation with the noise level much lower than the original PTV data. From hybrid unsteady velocity fields, we extract eigenfunctions using bi-orthogonal decomposition as a spatial problem for viscous instability. We also investigate stability/convergence characteristics of the hybrid simulation referring to linear stability analysis.

Direct Numerical Simulation of Naturally Evolving Free Circular Jet

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Trushar B. Gohil ◽  
Arun K. Saha ◽  
K. Muralidhar
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Direct Numerical Simulation ◽  
Near Field ◽  
Helical Structure ◽  
Far Field ◽  
Computational Domain ◽  
Reynolds Stresses ◽  
Self Similarity ◽  
Moderate Reynolds Number

Direct numerical simulation (DNS) of incompressible, spatially developing circular jets at a moderate Reynolds number of 1030 is performed to understand the details of the evolution of the flow field. The axisymmetric shear layer rolls up in the near field of the jet forming vortex rings. The rings tilt as they convect downstream before becoming turbulent in the far field. The evolution of vortical structures reveals the presence of a helical structure in the flow field along with the occurrence of vortex pairing. The time-averaged streamwise velocity distribution shows self-similarity in the far field. The cross-streamwise distribution of the Reynolds stresses also shows weak self-similarity downstream as the flow is not fully developed within the streamwise length of the computational domain. A detailed comparison with experiments is carried out and the computed time-averaged as well as statistical data shows excellent match with the experimental results. Numerical simulation also reveals various transitions during flow evolution in the streamwise direction.

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