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Automate the full OpenFOAM computational fluid dynamics (CFD) workflow — from case setup and mesh generation through solver execution to post-processing and visualization — using PyFoam, pyvista, and vtk.
When to Use This Skill
Use this skill when you need to:
Set up and run OpenFOAM cases programmatically (incompressible, multiphase, or turbulent flows).
Generate or modify blockMesh / snappyHexMesh dictionaries via Python.
Launch solvers (simpleFoam, interFoam, pisoFoam, etc.) and monitor convergence residuals in real time.
Post-process OpenFOAM results (velocity, pressure, vorticity) without opening the ParaView GUI.
Export simulation data to CSV, VTK, or image formats for reporting.
Automate parameter sweeps or sensitivity studies over multiple OpenFOAM runs.
This skill is not suitable for:
Structural or thermal FEA problems (see finite-element-analysis skill).
Combustion simulations requiring detailed chemistry (see cantera-combustion skill).
Real-time or hardware-in-the-loop control applications.
Background & Key Concepts
OpenFOAM Case Structure
Every OpenFOAM simulation lives in a case directory with a strict layout:
LogLineAnalyzer / FoamLogFile — parse solver log for residuals.
SolutionDirectory — introspect case structure.
pyvista / vtk Overview
pyvista provides a high-level Python API over vtk. OpenFOAM writes results in the VTK/ legacy format or as *.foam files readable by the OpenFOAM reader. pyvista can load these and perform slices, streamlines, isosurfaces, and rendering without a GUI.
Environment Setup
1. Install OpenFOAM
OpenFOAM must be installed natively on Linux or via Docker/WSL2 on Windows/macOS.
import PyFoam
import pyvista as pv
import vtk
import numpy as np
import matplotlib
import pandas as pd
print("PyFoam version :", PyFoam.__version__)
print("pyvista version :", pv.__version__)
print("vtk version :", vtk.vtkVersion.GetVTKVersion())
5. Docker alternative
# Pull the official OpenFOAM + PyFoam image
docker pull openfoam/openfoam2312-paraview510
# Run interactively
docker run -it --rm \
-v $(pwd)/cases:/cases \
openfoam/openfoam2312-paraview510 bash
Core Workflow
Step 1 — Build the Case Directory Structure
"""
create_case.py
Creates an OpenFOAM simpleFoam cavity case directory from scratch.
"""import os
import textwrap
from pathlib import Path
defwrite_file(path: Path, content: str) -> None:
path.parent.mkdir(parents=True, exist_ok=True)
path.write_text(textwrap.dedent(content))
print(f" wrote {path}")
defcreate_cavity_case(case_dir: str = "cavity") -> Path:
case = Path(case_dir)
# ---------- 0/ ----------
write_file(
case / "0" / "U",
"""\
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
dimensions [0 1 -1 0 0 0 0];
internalField uniform (0 0 0);
boundaryField
{
movingWall { type fixedValue; value uniform (1 0 0); }
fixedWalls { type noSlip; }
frontAndBack{ type empty; }
}
""",
)
write_file(
case / "0" / "p",
"""\
FoamFile
{
version 2.0;
format ascii;
class volScalarField;
object p;
}
dimensions [0 2 -2 0 0 0 0];
internalField uniform 0;
boundaryField
{
movingWall { type zeroGradient; }
fixedWalls { type zeroGradient; }
frontAndBack{ type empty; }
}
""",
)
# ---------- constant/ ----------
write_file(
case / "constant" / "transportProperties",
"""\
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object transportProperties;
}
nu [0 2 -1 0 0 0 0] 0.01;
""",
)
write_file(
case / "constant" / "turbulenceProperties",
"""\
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object turbulenceProperties;
}
simulationType laminar;
""",
)
# ---------- system/ ----------
write_file(
case / "system" / "blockMeshDict",
"""\
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object blockMeshDict;
}
scale 0.1;
vertices
(
(0 0 0) (1 0 0) (1 1 0) (0 1 0)
(0 0 0.1) (1 0 0.1) (1 1 0.1) (0 1 0.1)
);
blocks
(
hex (0 1 2 3 4 5 6 7) (20 20 1) simpleGrading (1 1 1)
);
boundary
(
movingWall { type wall; faces ((3 7 6 2)); }
fixedWalls { type wall; faces ((0 4 7 3)(2 6 5 1)(1 5 4 0)); }
frontAndBack{ type empty; faces ((0 3 2 1)(4 5 6 7)); }
);
""",
)
write_file(
case / "system" / "controlDict",
"""\
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object controlDict;
}
application icoFoam;
startFrom startTime;
startTime 0;
stopAt endTime;
endTime 0.5;
deltaT 0.005;
writeControl timeStep;
writeInterval 20;
purgeWrite 0;
writeFormat ascii;
writePrecision 6;
runTimeModifiable true;
""",
)
write_file(
case / "system" / "fvSchemes",
"""\
FoamFile { version 2.0; format ascii; class dictionary; object fvSchemes; }
ddtSchemes { default Euler; }
gradSchemes { default Gauss linear; }
divSchemes { default none; div(phi,U) Gauss linearUpwind grad(U); }
laplacianSchemes{ default Gauss linear corrected; }
interpolationSchemes { default linear; }
snGradSchemes { default corrected; }
""",
)
write_file(
case / "system" / "fvSolution",
"""\
FoamFile { version 2.0; format ascii; class dictionary; object fvSolution; }
solvers
{
p { solver PCG; preconditioner DIC; tolerance 1e-06; relTol 0.05; }
pFinal { $p; relTol 0; }
U { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-05; relTol 0; }
}
PISO { nCorrectors 2; nNonOrthogonalCorrectors 0; pRefCell 0; pRefValue 0; }
""",
)
print(f"\nCase directory created at: {case.resolve()}")
returncaseif __name__ == "__main__":
create_cavity_case("cavity")
Step 2 — Generate the Mesh and Run the Solver
"""
run_case.py
Runs blockMesh then icoFoam on the cavity case using PyFoam.
"""import subprocess
import sys
from pathlib import Path
from PyFoam.Execution.BasicRunner import BasicRunner
from PyFoam.RunDictionary.SolutionDirectory import SolutionDirectory
defrun_openfoam_case(case_dir: str = "cavity") -> None:
case = Path(case_dir).resolve()
ifnotcase.exists():
print(f"Case directory not found: {case}")
sys.exit(1)
sol = SolutionDirectory(str(case))
print(f"Case: {sol.name}")
print(f"Times available before run: {sol.getTimes()}")
# --- Step 2a: run blockMesh ---print("\n--- Running blockMesh ---")
mesh_runner = BasicRunner(
argv=["blockMesh", "-case", str(case)],
silent=False,
logname="blockMesh",
)
mesh_runner.start()
ifnot mesh_runner.runOK():
print("blockMesh FAILED — check blockMesh.logfile")
sys.exit(1)
# --- Step 2b: run icoFoam ---print("\n--- Running icoFoam ---")
solver_runner = BasicRunner(
argv=["icoFoam", "-case", str(case)],
silent=False,
logname="icoFoam",
)
solver_runner.start()
ifnot solver_runner.runOK():
print("icoFoam FAILED — check icoFoam.logfile")
sys.exit(1)
print("\nSolver finished successfully.")
print(f"Times available after run: {sol.getTimes()}")
if __name__ == "__main__":
run_openfoam_case("cavity")
Step 3 — Parse Residuals and Post-Process with pyvista
"""
postprocess.py
Reads icoFoam residuals, plots convergence, then loads VTK output
and renders a velocity magnitude slice.
"""import re
from pathlib import Path
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
import pyvista as pv
# ------------------------------------------------------------------# 3a: Parse solver log for residuals# ------------------------------------------------------------------defparse_residuals(log_path: str) -> pd.DataFrame:
"""Extract Time, Ux_residual, Uy_residual, p_residual from log."""
pattern_time = re.compile(r"^Time = ([\d.eE+\-]+)")
pattern_res = re.compile(
r"Solving for (\w+),\s+Initial residual = ([\d.eE+\-]+)"
)
records: list[dict] = []
current_time: float | None = Nonewithopen(log_path) as fh:
for line in fh:
m_time = pattern_time.match(line)
if m_time:
current_time = float(m_time.group(1))
records.append({"time": current_time})
m_res = pattern_res.search(line)
if m_res and records:
field = m_res.group(1)
residual = float(m_res.group(2))
records[-1][field] = residual
df = pd.DataFrame(records).set_index("time")
return df
defplot_residuals(df: pd.DataFrame, out_png: str = "residuals.png") -> None:
fig, ax = plt.subplots(figsize=(8, 4))
for col in df.columns:
ax.semilogy(df.index, df[col], label=col)
ax.set_xlabel("Time (s)")
ax.set_ylabel("Initial residual")
ax.set_title("icoFoam convergence residuals")
ax.legend()
ax.grid(True, which="both", linestyle="--", alpha=0.5)
fig.tight_layout()
fig.savefig(out_png, dpi=150)
print(f"Residual plot saved to {out_png}")
# ------------------------------------------------------------------# 3b: Load last time-step VTK and render velocity magnitude# ------------------------------------------------------------------defpostprocess_vtk(case_dir: str = "cavity", out_png: str = "velocity.png") -> None:
case = Path(case_dir)
# Convert to VTK first (OpenFOAM utility)import subprocess
subprocess.run(
["foamToVTK", "-case", str(case), "-latestTime"],
check=True,
)
# Find the last VTK internal mesh file
vtk_files = sorted((case / "VTK").glob("cavity_*.vtk"))
ifnot vtk_files:
print("No VTK files found — did foamToVTK run?")
return
mesh = pv.read(str(vtk_files[-1]))
print(f"Loaded: {vtk_files[-1].name}")
print(f" Bounds : {mesh.bounds}")
print(f" N cells: {mesh.n_cells}")
# Compute velocity magnitudeif"U"in mesh.array_names:
U = mesh["U"] # shape (N, 3)
mesh["U_mag"] = np.linalg.norm(U, axis=1)
# Slice at z = mid-plane
mid_z = 0.5 * (mesh.bounds[4] + mesh.bounds[5])
slc = mesh.slice(normal="z", origin=(0, 0, mid_z))
# Off-screen rendering
plotter = pv.Plotter(off_screen=True)
plotter.add_mesh(
slc,
scalars="U_mag",
cmap="turbo",
scalar_bar_args={"title": "Velocity magnitude (m/s)"},
)
plotter.add_axes()
plotter.view_xy()
plotter.screenshot(out_png)
print(f"Velocity magnitude plot saved to {out_png}")
if __name__ == "__main__":
log_file = "cavity/icoFoam.logfile"if Path(log_file).exists():
df = parse_residuals(log_file)
print(df.head())
plot_residuals(df)
postprocess_vtk("cavity")
Advanced Usage
A — Parameter Sweep with PyFoam ParsedParameterFile
"""
param_sweep.py
Runs icoFoam for multiple viscosity values and collects final p residuals.
"""import shutil
from pathlib import Path
import pandas as pd
from PyFoam.Execution.BasicRunner import BasicRunner
from PyFoam.RunDictionary.ParsedParameterFile import ParsedParameterFile
defsweep_viscosity(
base_case: str = "cavity",
nu_values: list[float] | None = None,
) -> pd.DataFrame:
if nu_values isNone:
nu_values = [0.005, 0.01, 0.02, 0.05]
results = []
for nu in nu_values:
run_dir = Path(f"cavity_nu{nu:.4f}")
shutil.copytree(base_case, str(run_dir), dirs_exist_ok=True)
# Modify viscosity
tp_path = run_dir / "constant" / "transportProperties"
tp = ParsedParameterFile(str(tp_path))
tp["nu"] = f"[0 2 -1 0 0 0 0] {nu}"
tp.writeFile()
# Run blockMesh + icoFoamfor util in ["blockMesh", "icoFoam"]:
runner = BasicRunner(
argv=[util, "-case", str(run_dir)],
silent=True,
logname=util,
)
runner.start()
# Collect last p residual from log
log = run_dir / "icoFoam.logfile"import re
last_p_res = Noneif log.exists():
for line in log.read_text().splitlines():
m = re.search(r"Solving for p,\s+Initial residual = ([\d.eE+\-]+)", line)
if m:
last_p_res = float(m.group(1))
re_num = 0.1 / nu # U_wall * L / nu (L=0.1, U=1)
results.append({"nu": nu, "Re": re_num, "final_p_res": last_p_res})
print(f" nu={nu:.4f} Re={re_num:.1f} p_res={last_p_res}")
return pd.DataFrame(results)
if __name__ == "__main__":
df = sweep_viscosity()
print(df.to_string(index=False))
df.to_csv("sweep_results.csv", index=False)
"""
interfoam_setup.py
Configures the alpha.water initial field and transportProperties
for an interFoam dam-break case.
"""from pathlib import Path
defwrite_alpha_field(case_dir: str, water_height: float = 0.3) -> None:
"""Write alpha.water field with water column from 0 to water_height."""
content = f"""\
FoamFile
{{
version 2.0;
format ascii;
class volScalarField;
object alpha.water;
}}
dimensions [0 0 0 0 0 0 0];
internalField uniform 0;
boundaryField
{{
atmosphere {{ type inletOutlet; inletValue uniform 0; value uniform 0; }}
walls {{ type zeroGradient; }}
defaultFaces{{ type empty; }}
}}
"""
path = Path(case_dir) / "0" / "alpha.water"
path.parent.mkdir(parents=True, exist_ok=True)
path.write_text(content)
print(f"alpha.water written (water_height hint={water_height} — set via setFields)")
defwrite_interfoam_transport(
case_dir: str,
nu_water: float = 1e-6,
nu_air: float = 1.48e-5,
rho_water: float = 1000.0,
rho_air: float = 1.0,
) -> None:
content = f"""\
FoamFile
{{
version 2.0;
format ascii;
class dictionary;
object transportProperties;
}}
phases (water air);
water
{{
transportModel Newtonian;
nu [0 2 -1 0 0 0 0] {nu_water};
rho [1 -3 0 0 0 0 0] {rho_water};
}}
air
{{
transportModel Newtonian;
nu [0 2 -1 0 0 0 0] {nu_air};
rho [1 -3 0 0 0 0 0] {rho_air};
}}
sigma [1 0 -2 0 0 0 0] 0.07;
"""
path = Path(case_dir) / "constant" / "transportProperties"
path.parent.mkdir(parents=True, exist_ok=True)
path.write_text(content)
print(f"transportProperties (interFoam) written to {path}")
if __name__ == "__main__":
write_alpha_field("damBreak")
write_interfoam_transport("damBreak")
Troubleshooting
T1 — "Cannot find patchField entry for …"
The boundary condition patch name in 0/ does not match the mesh patch names in constant/polyMesh/boundary. Run checkMesh -case <caseDir> and ensure every patch in the mesh has a corresponding entry in each initial field file.
T2 — Divergence / NaN residuals
Common causes and fixes:
# Check mesh quality — look for maxNonOrtho > 70 or negative volumes
checkMesh -case cavity
# Reduce Courant number (deltaT in controlDict)# For icoFoam: Co = U * deltaT / dx should stay < 1# Halve deltaT and double writeInterval to maintain same output frequency
# Programmatically lower deltaT using PyFoamfrom PyFoam.RunDictionary.ParsedParameterFile import ParsedParameterFile
from pathlib import Path
cd = ParsedParameterFile(str(Path("cavity") / "system" / "controlDict"))
cd["deltaT"] = 0.0025
cd.writeFile()
print("deltaT updated to 0.0025")
T3 — PyFoam "command not found"
# Ensure OpenFOAM environment is sourced BEFORE running Pythonsource /usr/lib/openfoam/openfoam2312/etc/bashrc
which icoFoam # should resolve to an OpenFOAM binary
T4 — pyvista cannot read VTK file
import pyvista as pv
# Use the OpenFOAM reader directly (no need for foamToVTK)
reader = pv.OpenFOAMReader("cavity/cavity.foam")
reader.set_active_time_value(reader.time_values[-1])
mesh = reader.read()
print(mesh.keys()) # list available datasets
internal = mesh["internalMesh"]
print(internal.array_names)
