Theory
The intensity is the root-mean-square velocity fluctuation divided by the mean velocity. Assuming the fluctuations are isotropic, the turbulent kinetic energy follows from it, equation (1); OpenFOAM's turbulentIntensityKineticEnergyInlet evaluates it every iteration with the velocity of each inlet face (OpenFOAM user guide, 2026). The specific dissipation rate follows from and the mixing length (Mixing length), equation (2).
With "Fully developed" (Inlet turbulence) this field is not used; the intensity is estimated as instead (about 0.04 at ).
Equations
| where | meaning | unit |
|---|---|---|
| Turbulence intensity | - | |
| Root-mean-square velocity fluctuation | m/s | |
| Velocity magnitude on the inlet face | m/s | |
| Turbulent kinetic energy | m²/s² | |
| Specific dissipation rate | 1/s | |
| Mixing length | m |
Default and rule
- Default
- Medium, 0.05 (used only with 'Intensity and length')
- Rule
0.05 (Medium).
- Source
Definitions as used by OpenFOAM's inlet conditions (OpenFOAM user guide, 2026). The preset levels (1 %, 5 %, 10 %) are the conventional low / medium / high classes; they are program presets, not values from a cited source.
Valid range > 0; presets 0.01 / 0.05 / 0.1
Typical values
About 0.01 behind a flow conditioner or in a quiet supply, 0.05 for ordinary pipe flow, 0.1 and more behind a fan, valve or engine.
Very small values
Below about 0.001 the inlet is tiny and the start-up can be slow; the solver keeps at least m²/s² in the starting field.