7 research outputs found
Dynamics of stable viscous displacement in porous media
We investigate the stabilization mechanisms of the invasion front in
two-dimensional drainage displacement in porous media by using a network
simulator. We focus on the process when the front stabilizes due to the viscous
forces in the liquids. We find that the capillary pressure difference between
two different points along the front varies almost linearly as function of
height separation in the direction of the displacement. The numerical results
support arguments that differ from those suggested earlier for viscous
stabilization. Our arguments are based upon the observation that nonwetting
fluid flows in loopless strands (paths) and we conclude that earlier suggested
theories are not suitable to drainage when nonwetting strands dominate the
displacement process. We also show that the arguments might influence the
scaling behavior between the front width and the injection rate and compare
some of our results to experimental work.Comment: The paper has been substantially revised. 12 papes, 10 figure
Dynamics and structure of interfacial crack fronts
The propagation of an interfacial crack front through a weak plane of a
transparent Plexiglas block has been studied experimentally. A stable crack in
mode I was generated by loading the system by an imposed displacement. The
local velocities of the fracture front line have been measured by using an high
speed CCD camera. The distribution of the velocities exhibits a power law
behavior for velocities larger than the average front velocity with a
crossover to a slowly increasing function for velocities lower than . The
fluctuations in the velocities reflect an underlying irregular bursts activity
with a power law distribution of the bursts. We further found that the size of
the local bursts scales differently in the direction parallel to and
perpendicular to the fracture front
Growth activity during fingering in a porous Hele Shaw cell
We present in this paper an experimental study of the invasion activity
during unstable drainage in a 2D random porous medium, when the (wetting)
displaced fluid has a high viscosity with respect to that of the (non-wetting)
displacing fluid, and for a range of almost two decades in capillary numbers
corresponding to the transition between capillary and viscous fingering. We
show that the invasion process takes place in an active zone within a
characteristic screening length from the tip of the most advanced finger. The
invasion probability density is found to only depend on the distance to the
latter tip, and to be independent of the value for the capillary number Ca. The
mass density along the flow direction is related analytically to the invasion
probability density, and the scaling with respect to the capillary number is
consistent with a power law. Other quantities characteristic of the
displacement process, such as the speed of the most advanced finger tip or the
characteristic finger width, are also consistent with power laws of the
capillary number. The link between the growth probability and the pressure
field is studied analytically and an expression for the pressure in the
defending fluid along the cluster is derived. The measured pressure are then
compared with the corresponding simulated pressure field using this expression
for the boundary condition on the cluster.Comment: 11 pages 10 figure
Granular Rayleigh-Taylor Instability: Experiments and Simulations
A granular instability driven by gravity is studied experimentally and
numerically. The instability arises as grains fall in a closed Hele-Shaw cell
where a layer of dense granular material is positioned above a layer of air.
The initially flat front defined by the grains subsequently develops into a
pattern of falling granular fingers separated by rising bubbles of air. A
transient coarsening of the front is observed right from the start by a finger
merging process. The coarsening is later stabilized by new fingers growing from
the center of the rising bubbles. The structures are quantified by means of
Fourier analysis and quantitative agreement between experiment and computation
is shown. This analysis also reveals scale invariance of the flow structures
under overall change of spatial scale.Comment: 4 pages, 11 figure