Flow Solvers
Note, that in the following there is a difference between porous materials and porous voxels. A flow simulation is run on a material, e.g., glass fibers, where the pores are filled with air. Thus, highly porous material is a material with more fluid voxels than solid voxels, e.g., 70% air and 30% glass fibers. Additionally, the solid voxels can be defined as porous, if the pores in a material are too small to be resolved.
To solve the partial differential equations describing the fluid flow, three solution methods, called solvers, are available in FlowDict:
LIR
The LIR (Left Identity Right) solver uses a non-uniform adaptive grid which results in very low memory requirements. While the LIR solver’s speed is comparable to the SimpleFFT solver for low porous materials, it is very fast (and should be chosen) for highly porous materials. See Linden et al. (2015) for more information.
It can be used to solve the Stokes, Darcy Flow, Stokes-Brinkman, Navier-Stokes, and Navier-Stokes-Brinkman equations.
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SimpleFFT
The SimpleFFT (Simple Fast Fourier Transform) solver takes longer to converge for highly porous materials and requires more memory, but it can deal with non-linear (non-laminar) fluid flow as well as with linear flow. Therefore, faster flows, which are not necessarily laminar and are modeled by the Navier-Stokes equation can be computed with the SimpleFFT solver.
The solver can also deal with porous voxels and thus solves the Stokes-Brinkman and Navier-Stokes-Brinkman equations.
The SimpleFFT solver is very fast for low porosity materials and is a much better choice than the EJ solver for this type of materials.
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EJ
The EJ (Explicit Jump) solver is very fast for highly porous materials and has low memory requirements but can only be applied to flows when the pressure drop/flow velocity dependence is linear (laminar), i.e., for the Stokes equation and Darcy Flow only.
For Stokes simulations, the EJ solver should not be used for low porous materials (50% or less porosity) such as reservoir rocks or ceramics. For these kinds of materials, the SimpleFFT or LIR solver perform much better.
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