A defensible CFD model is not defined by attractive contours. Confidence comes from a chain of checks: correct physical formulation, suitable mesh, stable numerical solution, mesh and time independence, and comparison with reference data.
1. Define the physics before the software
Flow regime, properties, boundary conditions, turbulence model and multiphysics assumptions must be defined before building the numerical model. Many CFD errors start with an unsuitable mathematical model, not solver settings.
2. Measure mesh independence using the target quantity
At least three mesh levels are a useful starting point. Compare the decision-driving output—pressure drop, force coefficient, vibration amplitude, Nusselt number or heat-transfer rate—not residuals alone.
3. Assess convergence in multiple ways
- Adequate residual reduction
- Stability of monitored quantities
- Closure of mass and energy balances
- Physically reasonable flow-field behaviour
4. Separate verification from validation
Verification asks whether the equations were solved correctly; validation asks whether the selected equations represent reality adequately. Both are necessary and neither replaces the other.