26 CFD TECHNICAL CASES
Start with the symptom. Follow the physics to the cause.
These cases are written for engineers who already have a simulation and need to understand why it diverges, disagrees with expectations, violates conservation or depends too strongly on mesh, timestep, boundary conditions or model choices.
When a solver stops behaving—or appears to behave too well.
Separate numerical failure, physical unsteadiness, incomplete convergence and false confidence in a converged but incorrect result.
CFD Simulation Diverges
Check units, boundaries, mesh, initialization, physics and numerics in a diagnostic order that preserves causality.
Open case →PUBLISHEDRESIDUALSResiduals Oscillate or Do Not Converge
Distinguish physical unsteadiness from numerical instability, boundary feedback and mesh-driven convergence problems.
Open case →NEWFALSE CONVERGENCECFD Converged but Results Look Wrong
Low residuals do not prove that the mesh, boundary conditions, physics or engineering answer are correct.
Open case →NEWCONSERVATIONMass Imbalance in CFD
Build the complete control-volume balance and distinguish incomplete convergence from physical accumulation or missing flux paths.
Open case →Find where mesh decisions change the physics.
Use spatial diagnostics, near-wall consistency and mesh-sequence evidence rather than a single global quality number.
Bad Mesh Quality in CFD
Locate the worst cells, correlate them with important gradients and repair the geometry or meshing mechanism that creates them.
Open case →NEWPRISM LAYERSPrism Layers Collapse or Disappear
Diagnose narrow gaps, curvature, sharp corners, total thickness, growth and surface-resolution conflicts.
Open case →PUBLISHEDY+Solved y+ Misses the Target
Understand why estimated and solved wall shear differ and how to remesh from the solved y+ field.
Open case →NEWTURBULENCE / WALLSTurbulence & Wall-Treatment Mismatch
Align RANS model, wall treatment, first-cell height, prism stack and solved y+ with the quantity of interest.
Open case →NEWGRID VERIFICATIONGrid-Independence Study Does Not Converge
Diagnose oscillatory mesh trends, weak refinement ratios, non-asymptotic behavior and misleading GCI evidence.
Open case →When the result depends on how the domain is connected to the physical system.
Challenge boundary placement, pressure definitions and turbulence inputs before tuning solver controls.
Reverse Flow at a Pressure Outlet
Separate physical recirculation from poor outlet placement, startup effects and boundary inconsistency.
Open case →NEWDOMAIN SIZEOutlet Boundary Too Close
Test wake recovery, gradients and pressure-outlet sensitivity instead of relying on a fixed downstream-distance rule.
Open case →PUBLISHEDINTERNAL FLOWCFD Pressure Drop Does Not Match
Align pressure definitions and stations, then check local losses, wall treatment, roughness, flow regime and mesh.
Open case →NEWINLET TURBULENCEInlet Turbulence Conditions Look Wrong
Connect intensity and length scale to k, ε and ω, then quantify whether uncertain inlet turbulence changes the result.
Open case →Trace coupled physics through interfaces rather than treating them as solver-only problems.
These cases connect thermal resistances, phase interfaces and moving-mesh coupling to conservation and resolution.
CHT Temperature or Energy Balance Looks Wrong
Trace heat from source to solid, interface, fluid and outlet to identify the resistance or boundary that controls the error.
Open case →NEWTHERMAL CONTACTCHT Contact Resistance & Temperature Jump
Distinguish a physically correct interface temperature jump from unit errors, duplicated resistance or broken coupling.
Open case →PUBLISHEDVOF / MULTIPHASEVOF Interface Is Unstable or Smeared
Diagnose timestep, mesh, initialization and boundary effects that diffuse or destabilize the phase interface.
Open case →NEWOVERSET MESHOverset Mesh Interpolation, Holes & Orphans
Check overlap, donor coverage, hole cutting, cell-size compatibility, motion envelope and conservation.
Open case →Challenge the modelling choices that control time and comparison.
These cases focus on temporal resolution, rotor-stator coupling and the evidence required to compare CFD against reality.
CFD Time-Step Sensitivity
Connect Δt to Courant number, dominant frequencies, interface motion and timestep-independent engineering outputs.
Open case →NEWROTATING FLOWMRF & Sliding-Mesh Interface Problems
Check rotating method, axis/frame definition, interface mesh compatibility, periodicity and transient resolution.
Open case →NEWVALIDATIONCFD Results Do Not Match Experiment
Separate comparison error, test uncertainty, numerical uncertainty, uncertain inputs and model-form error.
Open case →Six additional cases deepen the highest-value CFD problem clusters.
The Technical Case library now contains 26 symptom-led diagnostics. The focused additions cover meshing, convergence, pressure boundaries, thermal/CHT, VOF conservation and rotating-machinery performance.
Prism Stack Too Thin for the Boundary Layer
Diagnose a prism stack that achieves first-cell y+ but ends while important wall-normal gradients are still strong.
Open case →NEWCONVERGENCE & TROUBLESHOOTINGResiduals Are Low but Monitors Still Drift
Diagnose slow engineering-output drift after residuals appear flat, and separate incomplete convergence from physical unsteadiness.
Open case →NEWINTERNAL FLOW & PRESSURE DROPFlow Rate Is Wrong with Pressure Boundaries
Trace unexpected mass flow to pressure definitions, reference pressure, system resistance, properties, boundaries or conservation errors.
Open case →NEWTHERMAL & CHTCFD Heat Transfer Coefficient Looks Wrong
Diagnose h or Nusselt disagreement from reference temperature, heat flux, averaging, wall treatment, mesh, properties and energy balance.
Open case →NEWMULTIPHASE & VOFVOF Phase Volume or Mass Is Not Conserved
Close the phase inventory using boundary fluxes and sources before testing timestep, interface transport, clipping and report definitions.
Open case →NEWTURBOMACHINERYCFD Torque or Power Is Wrong in Rotating Machinery
Check moment axis, origin, RPM conversion, rotating wall selection, sign, interfaces and cycle averaging before changing flow physics.
Open case →Use the public cases first. Escalate when the diagnosis depends on your actual model.
For a focused review, submit the engineering objective, software, current model stage, symptom, checks already performed and non-confidential evidence.
Pair the diagnostic workflow with an independent engineering check.
Use Abecator calculators and advisors to quantify the expected scale, then escalate only when the Technical Case shows that the remaining uncertainty is specific to your CFD model.