文档介绍：Porous Media Modeling
Workshop
Topics of Workshop
Introduction to FLOW-3D®’s drag model
The saturated porous media model
Understanding the drag coefficient and its relation to permeability
Dealing with anisotropy
The unsaturated porous media model
Understanding FLOW-3D®’s Drag Model
Flow regions with many small obstructions too small to resolve must be modeled by distrubuted resistance:
K is the drag coefficient. It represents the flow resistance in the porous medium.
Total acceleration
Inertia
Acc. due to press. gradient
Accel. due to viscosity
Accel. due to gravity
Drag effects
Vf= Volume fraction (porosity) putational cell
Af= Diagonal tensor area fractions of cell
Saturated porous media
Useful for situations where there exists a well-defined saturation front with the porous material
Model assumes that saturated regions are separated from “dry” regions by a thin saturation front
Pressure difference across this saturation front is dictated by a user-defined capillary pressure (Pcap)
d
a
fluid in a pore
s
Concave case (lower pressure in liquid) is assumed to have +ve Pcap
The drag coefficient
or
Relationship between drag & permeability
Often confusion arises between D’Arcy permeability (κ) and the drag coefficient (K). The relationship is:
Thus, a material with ∞ drag represents 0 permeability
“Drag coefficient” in FLOW-3D output is:
This can vary between 0 (infinite drag) and 1 (zero drag) and is dimensionless
and
Setting up a problem with saturated porous media
Activate drag model of choice
Create ponent(s)
ponent can posed of various ponents and/or STL files to create plex shapes
Specify porosity, capillary pressure and drag coefficients for ponent
ponent can have different properties
Modeling anisotropic materials with FLOW-3D®
Permeability can be anisotropic, which means that the permeability can differ by direction of flow
In FLOW-3D®, the user can specify directional porosities, which control the area fraction (Af) values i