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CHT Turbulence

Video topic: why turbulence-model choice matters in CHT, what models the industry actually offers, and how our own auto-selection compares. Pooled from multiple Sources entries below.

Talking points:

  • Why it matters at all — turbulence model choice swings the result, not just the runtime: laminar pipe flow Nu≈3.66 vs. turbulent Nu>100, a 2–10x jump in convective h from the same geometry/flow rate depending on regime. (Neural Concept)
  • Reading the regime off Reynolds number — worked example: a tight electronics enclosure with channel-spacing-derived Re≈870 is laminar, not turbulent; picking the wrong regime by assumption rather than by calculation is a common setup mistake. (Ansys FLUENT chip-on-board tutorial)
  • The industry's turbulence-model menu — this varies a lot by tool: kOmegaSST (common CHT default, wall-function based), Realizable k-epsilon (SimFlow's pick for electronics-cooling flows), LES Smagorinsky (SimScale, eddy-resolving, needs cutoff-length/delta-coefficient tuning), SST-intermittency transition models (Ansys FENSAP-ICE, resolves the laminar-to-turbulent transition itself rather than switching hard between regimes).
  • Steady vs. transient turbulence — LES and transition modeling are inherently eddy-resolving/transient techniques; a steady-state solver by construction can't offer them. Worth being upfront about this as a scope boundary, not a missing checkbox.
  • Our own angle — trafolo-thermal auto-selects laminar vs. kOmegaSST via Rayleigh/Reynolds thresholds (Ra ≥ 1e9 or Re ≥ 5e5), with a manual override (auto / laminar / kOmegaSST). Good contrast piece against tools that expose a full turbulence-model picker: automatic-by-default vs. manual-by-default, and why that's a deliberate simplicity trade-off for a steady h-estimator.

Sources:

  • Simscale — CHT Analysis docs entry (turbulence model selection, LES Smagorinsky)
  • Neural Concept — turbulence model vs. Nusselt number entry
  • SimFlow [UNAVAILABLE -- was: https://trafolo.atlassian.net/wiki/spaces/Documentat/pages/581304343/SimFlow] — electronics-cooling turbulence model entry
  • Ansys [UNAVAILABLE -- was: https://trafolo.atlassian.net/wiki/spaces/Documentat/pages/581271553/Ansys] — FLUENT chip-on-board (Re-based regime pick) and FENSAP-ICE (transition modeling) entries