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CFD–DEM simulation

CFD–DEM simulation​

Phynexis couples discrete-element solids with fluid solvers based on OpenFOAM, using solver variants such as hybridCFDdem, interIBdem, and semiResolvedCFDdem. This page describes how to run bundled OpenFOAM-style cases that ship with the licensed Phynexis / CFDDEM source tree.

:::info Engine vs this website

Paths such as cfddem/examples/... refer to directories inside your engine checkout, not the Examples section of this documentation site. The site Examples are standalone Python scripts; CFD–DEM tutorials live next to OpenFOAM case files in the distribution you received.

:::

Prerequisites​

  • A supported OpenFOAM environment compatible with your Phynexis build (see your distributor’s release notes).
  • Phynexis Python bindings available to the case scripts (typically via pip / wheel as in Installation, or a developer build path—see below).
  • Familiarity with OpenFOAM case layout (system/, constant/, 0/).

Case layout and drivers​

Coupled cases use the usual OpenFOAM directory structure. DEM coupling is driven from Python (for example createDEM.py) while the fluid mesh and fields follow OpenFOAM conventions. In each case, system/fvSolution → coupling names the DEM script and callback used for that run—adjust there when you switch coupling strategies or DEM inputs.

Running bundled examples​

Example cases live under the examples/ folder inside the cfddem tree of your source distribution (not under this repo). From an example directory you will typically use the provided Allwclean / Allrun scripts, for example:

./Allrun

Use ./Allrun-parallel when the case ships it for parallel mesh decomposition.

If import phynexis fails inside createDEM.py, insert the library path for your build before importing, for example:

import sys
sys.path.append("/path/to/phynexis/build/lib/")
import phynexis

Use the actual lib path from your installation or build instructions.

Water entry example (interIBdem)​

Illustrative workflow (paths relative to your cfddem checkout):

  1. Copy the case tree to a writable location:

    cd cfddem
    cp -rf examples/interIBdem/water_entry local/interIBdem/

  2. Run (after checking system/fvSolution → coupling points at the intended DEM script):

    cd local/interIBdem/water_entry
    ./Allclean
    ./Allrun-parallel

  3. If execution fails, verify the Phynexis library path in createDEM.py matches the directory that contains your built Python modules.

Visualization​

  • Open interIBdem.foam in ParaView for the fluid fields; set Case Type to Decomposed Case when working with decomposed meshes, and optionally disable Skip Zero Time.
  • DEM VTK sequences typically appear under dem/ (for example particle_mesh_*.vtk.series). For spherical particles you can group series and map velocities with ParaView filters; for CFD–fluid interfaces, a Contour on alpha.water at 0.5 is common for two-phase surfaces.

General ParaView workflows for Phynexis VTK output (particles, walls, contact tubes, rendering) are centralized in ParaView rendering.

Modifying the water-entry case​

  • Fluid properties — constant/transportProperties; phase names must stay consistent with alpha.<phase> fields (for example in system/setFieldsDict).
  • Mesh / geometry — system/blockMeshDict. If a length scale is applied there, vertex coordinates are multiplied accordingly when the mesh is built.
  • Mesh resolution — controlled by the refinement near simpleGrading in the blocks → hex entry; prefer nearly cubic cells when possible.
  • Initial volume fractions — system/setFieldsDict. Scaling from blockMeshDict does not apply here: coordinates are physical. A box entry such as box (-0.05 -0.05 -0.15) (0.05 0.05 0.03) sets lower-front-left and upper-back-right corners. Ensure alpha.<phase> names match transportProperties → phases.
  • Time control — system/controlDict (end time, Δt, write interval).
  • DEM setup — in createDEM.py, functions such as oneSphere() adjust DEM domain size, walls, and insertion regions. Parameters named scale may scale the overall DEM box and insertion zone, while p_size often sets the physical particle diameter—check the function body for your case variant.

For licensing, binaries, or case packs not present in your tree, use the contact channel on About.