OpenFOAM Case Structure and Solver Configuration

Описание: OpenFOAM is a black box to most engineers. It's not. It's just organized.

A complete CFD case has three directories, each with a specific purpose. Understanding this structure is the key to running and debugging simulations.

CASE DIRECTORY STRUCTURE:

wrench-template/
├── system/ (Solver settings)
├── constant/ (Physics constants, mesh)
├── 0/ (Initial and boundary conditions)
├── Allrun (Batch script)
└── Allclean (Cleanup script)

SYSTEM/ - The Brain:

Contains dictionaries that tell OpenFOAM how to solve the equations.

system/controlDict:
startTime, endTime: Iteration or physical time range
deltaT: Time step (for transient) or iteration step (steady-state)
writeInterval: How often to save results

For simpleFoam (steady state): We run 1000+ iterations until convergence.

system/fvSchemes:
Discretization schemes for gradients, divergence, Laplacian
Example: gradSchemes { default Gauss linear; } (central differences)

system/fvSolution:
Solver settings for pressure, velocity (PCG, PBiCG, smoothSolver)
Relaxation factors (0.3-0.7 for stability)
Convergence tolerance (1e-6)

system/snappyHexMeshDict:
Meshing parameters (geometry, refinement levels, inflation)

CONSTANT/ - The Physics:

Contains mesh and properties that don't change.

constant/triSurface/:
wrench.stl (your geometry)

constant/polyMesh/:
points: Vertex coordinates
faces: Cell connectivity
owner: Which cell owns each face
boundary: Boundary patch definitions

Generated by blockMesh and snappyHexMesh.

constant/transportProperties:
nu (kinematic viscosity) = 1.5e-05 m²/s for air
rho (density) = 1.225 kg/m³

constant/turbulenceProperties:
turbulenceModel: kEpsilon (or kOmegaSST)
simulationType: RAS (Reynolds-Averaged Simulation)

0/ - The Initial Conditions:

The starting point for all fields.

0/p (pressure):
internalField: uniform 0 (gauge pressure, relative to atmospheric)
boundaryField: Conditions at inlet, outlet, walls

0/U (velocity):
internalField: uniform (20 0 0) m/s (inlet velocity)
boundaryField: noSlip at walls, fixedValue at inlet, zeroGradient at outlet

0/k and 0/epsilon:
Turbulent kinetic energy and dissipation rate
Initialized from inlet conditions
Boundary conditions: turbulentIntensityKineticEnergyInlet (5%), zeroGradient at outlet

POSTPROCESSING:

After simulation converges, we extract:

postProcessing/forceCoeffs1/0/forceCoeffs.dat:
Drag coefficient (Cd)
Lift coefficient (Cl)
Pressure coefficient (Cp) along surface

This single file the Cd value is what Dakota uses to optimize our design.

THE DATA FLOW:

Parameters.in (from Dakota) → wrench_parametric.py → wrench.stl → blockMesh/snappyHexMesh → simpleFoam → forceCoeffs.dat → dakota_driver.py → Results.out

Each step transforms the input into the next stage's input.

NEXT STEP:

Tomorrow we run the simulation. We'll watch it converge, extract the drag coefficient, and celebrate our first CFD result.

simpleFoam or pimpleFoam? Why choose one over the other?

#OpenFOAM #CFD #Simulation #ComputationalFluidDynamics #Engineering #Solver #Day8