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Steps of a CFD analysis

Short answer

Pre-processing defines geometry, generates mesh, selects physics and boundary conditions. The solver discretises the governing equations, applies pressure-velocity coupling such as SIMPLE, and iterates until residuals fall to tolerance. Post-processing plots contours, extracts forces and pressure drop, and checks mesh independence and validation.

Explain the three main stages of a CFD simulation with the activities carried out in each stage. Draw a flowchart of the procedure.

A CFD analysis has three stages: pre-processing, solving and post-processing.

 Problem definition
        |
        v
+---------------------+
| 1. PRE-PROCESSING   |  geometry, mesh,
|                     |  physics, BCs
+---------------------+
        |
        v
+---------------------+
| 2. SOLVER           |<--+ not converged
|  discretise, iterate|   |
+---------------------+---+
        | converged
        v
+---------------------+
| 3. POST-PROCESSING  |  plots, forces,
|                     |  validation
+---------------------+

1. Pre-processing

  1. Define the problem and the aim (e.g. pressure drop, lift).
  2. Create or import the geometry (CAD) and clean it; choose the computational domain size.
  3. Generate the mesh (structured/unstructured) and refine near walls and gradients.
  4. Select the physical models: laminar/turbulent, steady/transient, compressible/incompressible, heat transfer.
  5. Define fluid properties and boundary and initial conditions (inlet velocity, outlet pressure, wall, symmetry).

2. Solver

  1. The governing equations are integrated over control volumes (FVM) or approximated by differences (FDM) to give algebraic equations.
  2. A pressure-velocity coupling method (e.g. SIMPLE) and linear solvers (Gauss-Seidel, multigrid) solve them iteratively.
  3. Iteration continues until the residuals fall to a set tolerance (e.g. 10−410^{-4} to 10−610^{-6}) and monitored quantities stop changing.

3. Post-processing

  • Contour, vector and streamline plots, line plots, animations.
  • Integrated results: forces, pressure drop, heat transfer rate, mass-flow balance.
  • Check mesh independence and compare with experimental or analytical data (verification and validation).
  • If results are unsatisfactory, return to the mesh or the model and repeat.

✓ Answer checked by Claude Opus 5.5 (high effort)

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