CFD TOPIC HUB · CONVERGENCE & TROUBLESHOOTING
CFD convergence and troubleshooting: find the first bad physics, not the last error message.
Use this hub when a solver diverges, residuals stall, results look suspicious, conservation is poor or the solution depends strongly on numerics, boundaries or initialization.
Start from the decision the CFD model has to support.
Convergence is evidence, not proof. The fastest diagnostic path usually starts by localizing the first non-physical field or imbalance and then testing one cause class at a time.
Use these checks before adding model complexity.
- Check units, properties and boundary conditions before tuning numerical controls.
- Track field extrema, conservation and engineering monitors alongside residuals.
- Change one cause class at a time so the diagnostic process preserves causality.
Already have a CFD model that behaves incorrectly?
Start from the symptom and follow the Technical Case diagnostic sequence before tuning unrelated solver controls.
Browse Technical Cases →Build the modelling decision from the underlying physics.
Use the guides for definitions, assumptions, workflow design and evidence requirements.
Courant Number, CFL & Time Step
Screen transient numerical resolution
Open resource →ENGINEERING GUIDECFD Verification vs Validation
Separate convergence from credibility
Open resource →ENGINEERING GUIDESTAR-CCM+ Residuals & Convergence Monitoring
Solver-specific monitoring workflow
Open resource →Diagnose the failure mode when the solved model disagrees.
Technical Cases are organized around symptoms, likely causes, diagnostic order and controlled fixes.
CFD Simulation Diverges
Diagnose units, BCs, mesh, initialization, physics and numerics
Open resource →TECHNICAL CASEResiduals Oscillate or Do Not Converge
Separate physical unsteadiness from numerical instability
Open resource →TECHNICAL CASECFD Converged but Results Look Wrong
Challenge false convergence
Open resource →TECHNICAL CASEMass Imbalance in CFD
Trace continuity and missing flux paths
Open resource →TECHNICAL CASEReverse Flow at a Pressure Outlet
Separate physical recirculation from boundary problems
Open resource →Challenge the CFD with transparent engineering checks.
Independent calculations help reveal whether the problem is in the physics, inputs, numerical resolution or interpretation.
Continue with the same engineering context.
Move into structured training when you need the complete methodology, or engineering support when the answer depends on the actual project.
Connect adjacent modelling decisions.
Complex CFD problems often cross more than one topic cluster. Continue into the governing issue rather than searching by software menu alone.
Go deeper on a question engineers search when the model becomes uncertain.
These focused resources extend this topic cluster with one decision guide and one symptom-led Technical Case.
CFD Convergence Criteria
Judge convergence from residuals, engineering monitors, conservation and stationarity rather than a single residual threshold.
Read guide →TECHNICAL CASEResiduals Are Low but Monitors Still Drift
Diagnose slow engineering-output drift after residuals appear flat, and separate incomplete convergence from physical unsteadiness.
Open diagnostic case →