Transport by Two-Dimensional Random Velocity Fields : Effective Dispersion Coefficients of a Finite Plume

1994 ◽  
pp. 113-126 ◽  
Author(s):  
Gedeon Dagan
Keyword(s):  
Velocity Fields ◽  
Two Dimensional ◽  
Dispersion Coefficients ◽  
Random Velocity ◽  
Effective Dispersion

Gaseous dispersion in laminar flow through a circular tube

1965 ◽  
Vol 284 (1399) ◽  
pp. 540-550 ◽  
Keyword(s):  
Circular Tube ◽  
Dispersion Coefficient ◽  
Straight Tube ◽  
Laminar Regime ◽  
Thermal Conductivity Detector ◽  
Longitudinal Dispersion Coefficient ◽  
Dispersion Coefficients ◽  
Effective Dispersion ◽  
Flow Through ◽  
Gaseous Dispersion

The dispersion of a pulse of ethylene injected into nitrogen, flowing in the laminar régime through straight and curved tubes, has been investigated at pressures of 1.0 and 4.4 atm. From the study of the concentration profiles with a thermal conductivity detector (katharometer) it is found that the experimental results for gas velocities between 1.00 and 16.00 cm/s agree well with the analytical solution to this problem for a straight tube given by Sir Geoffrey Taylor and extended by Aris. In particular, at low velocities, the effective dispersion coefficients tend to the molecular diffusivities. The presence of a bend slightly reduces the effective longitudinal dispersion coefficient and the introduction of constrictions enhances it. Data are also given on a number of other gas pairs. It is concluded that measurements of dispersion provide an accurate and simple way of studying diffusion in gas mixtures.

Upscaling of pore-scale mixing and reaction through effective dispersion coefficients

2021 ◽  
Author(s):  
Alexandre Puyguiraud ◽  
Lazaro Perez ◽  
Juan J. Hidalgo ◽  
Marco Dentz
Keyword(s):  
Green Function ◽  
Molecular Diffusion ◽  
Early Time ◽  
Hydrodynamic Dispersion ◽  
Pore Scale ◽  
Dispersion Coefficients ◽  
Incomplete Mixing ◽  
Effective Dispersion ◽  
Structure Heterogeneity ◽  
Field Heterogeneity

<p>We utilize effective dispersion coefficients to capture the evolution of the mixing interface between two initially segregated species due to the coupled effect of pore-scale heterogeneity and molecular diffusion. These effective dispersion coefficients are defined as the average spatial variance of the solute plume that evolves from a pointlike injection (the transport Green function). We numerically investigate the effective longitudinal dispersion coefficients in two porous media of different structure heterogeneity  and through different Péclet number regimes for each medium. We find that, as distance traveled increases (or time spent), the solute experiences the pore-scale velocity field heterogeneity due to advection and transverse diffusion, resulting in an evolution of the dispersion coefficients. They evolve from the value of molecular diffusion at early time, then undergo an advection dominated regime, to finally reach the value of hydrodynamic dispersion at late times. This means that, at times smaller than the characteristic diffusion time, the effective dispersion coefficients can be notably smaller than the hydrodynamic dispersion coefficient. Therefore, mismatches between pore-scale reaction data from experiment or simulations and Darcy scale predictions based on temporally constant hydrodynamic dispersion can be explained through these differences. We use the effective dispersion coefficients to approximate the transport Green function and to quantify the incomplete mixing occurring at the pore-scale. We evaluate the evolution of two initially segregated species via this methodology. The approach correctly predicts the amount of chemical reaction occuring in reactive bimolecular particle tracking simulations. These results shed light on the upscaling of pore-scale incomplete mixing and demonstrates that the effective dispersion is an accurate measure for the width of the mixing interface between two reactants. </p>

Ergodic Simulations for Diffusion in Random Velocity Fields

2008 ◽  
pp. 659-668 ◽  
Author(s):  
Nicolae Suciu ◽  
Călin Vamos ◽  
Karl Sabelfeld
Keyword(s):  
Velocity Fields ◽  
Random Velocity

scholarly journals Quasi-periodic forces and conditionally averaged characteristics of unsteady cavitation flow around a hydrofoil

2021 ◽  
Vol 2119 (1) ◽  
pp. 012030
Author(s):  
E I Ivashchenko ◽  
M Yu Hrebtov ◽  
R I Mullyadzhanov
Keyword(s):  
Reynolds Number ◽  
Liquid Phase ◽  
High Reynolds Number ◽  
Velocity Fields ◽  
Large Eddy Simulations ◽  
Two Dimensional ◽  
Cavitation Flow ◽  
Large Eddy ◽  
High Reynolds ◽  
Conditional Averaging

Abstract Large-eddy simulations are performed to investigate the cavitating flow around two dimensional hydrofoil section with angle of attack of 9° and high Reynolds number of 1.3×106. We use the Schnerr-Sauer model for accurate phase transitions modelling. Instantaneous velocity fields are compared successfully with PIV data using the methodology of conditional averaging to take into account only the liquid phase characteristics as in PIV. The presence of two frequencies in a spectrum corresponding to the full and partial cavity detachments is analysed.

Conditions for the Separability of Objects in Two-Dimensional Velocity Fields

1992 ◽  
Vol 35 (4) ◽  
pp. 484-491
Author(s):  
Stephan Foldes
Keyword(s):  
Velocity Field ◽  
Directed Graph ◽  
Velocity Fields ◽  
Sufficient Condition ◽  
Two Dimensional ◽  
Jordan Curves ◽  
Directed Cycles

AbstractWe consider the directed graph representing the obstruction relation between objects moving along the streamlines of a two-dimensional velocity field. A collection of objects is sequentially separable if and only if the corresponding graph has no directed cycles. A sufficient condition for this is the permeability of closed Jordan curves.

scholarly journals The Dark Matter Content of Barred Spiral Galaxies

2004 ◽  
Vol 220 ◽  
pp. 277-278
Author(s):  
Glen Petitpas ◽  
Mousumi Das ◽  
Peter Teuben ◽  
Stuart Vogel
Keyword(s):  
Dark Matter ◽  
Spiral Galaxies ◽  
Velocity Fields ◽  
Matter Content ◽  
Two Dimensional ◽  
Disk Model ◽  
Barred Galaxies ◽  
Preliminary Results ◽  
Nearby Galaxies ◽  
Barred Spiral Galaxies

Two-dimensional velocity fields have been used to determine the dark matter properties of a sample of barred galaxies taken from the BIMA Survey of Nearby Galaxies (SONG). Preliminary results indicate that the maximal disk model is not appropriate in several galaxies in our sample, but higher resolution results will be needed to confirm this.

scholarly journals Acquisition of a 3 min, two-dimensional glacier velocity field with terrestrial radar interferometry

2017 ◽  
Vol 63 (240) ◽  
pp. 629-636 ◽  
Author(s):  
DENIS VOYTENKO ◽  
TIMOTHY H. DIXON ◽  
DAVID M. HOLLAND ◽  
RYAN CASSOTTO ◽  
IAN M. HOWAT ◽  
...  
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Feature Tracking ◽  
High Spatial Resolution ◽  
Velocity Fields ◽  
Radar Interferometry ◽  
Line Of Sight ◽  
Two Dimensional ◽  
Outlet Glacier ◽  
Glacier Velocity

ABSTRACTOutlet glaciers undergo rapid spatial and temporal changes in flow velocity during calving events. Observing such changes requires both high temporal and high spatial resolution methods, something now possible with terrestrial radar interferometry. While a single such radar provides line-of-sight velocity, two radars define both components of the horizontal flow field. To assess the feasibility of obtaining the two-dimensional (2-D) flow field, we deployed two terrestrial radar interferometers at Jakobshavn Isbrae, a major outlet glacier on Greenland's west coast, in the summer of 2012. Here, we develop and demonstrate a method to combine the line-of-sight velocity data from two synchronized radars to produce a 2-D velocity field from a single (3 min) interferogram. Results are compared with the more traditional feature-tracking data obtained from the same radar, averaged over a longer period. We demonstrate the potential and limitations of this new dual-radar approach for obtaining high spatial and temporal resolution 2-D velocity fields at outlet glaciers.

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