Field initialization and starting guesses
Vanellus starts every API simulation from internally generated fields. These provide the starting point for the steady solve. In thermally isolated regions, the starting temperature also sets the region’s total thermal energy.
Initial fields
Before the first SIMPLE iteration, Vanellus initializes:
| Quantity | Initial value |
|---|---|
| Velocity | Zero in every fluid cell |
| Pressure | Zero relative pressure |
| Volumetric face flux | Zero on every face |
| Temperature | The reference temperature in every solved cell |
tke and sdr | Uniform values derived from representative inlet quantities |
Where temperature-setting boundaries determine the steady temperature, the initial temperature is a numerical starting guess. In an isolated thermal region, the reference instead selects the conserved thermal energy: the heat-capacity-weighted mean temperature remains at that value as heat redistributes. See reference temperature for the weighting and selection rules.
SIMPLE iterations are not physical time steps, so these initial fields do not describe a startup transient.
Turbulence fields
For k–ω SST, Vanellus initializes the complete fluid region using representative inlet speed, turbulent_intensity, and viscosity_ratio. It takes the largest value of each quantity across the inlet definitions. For a fan, the representative speed is the largest supplied curve flow rate divided by the meshed opening area. Internal fallback values are used if no inlet supplies a non-zero quantity.
The resulting uniform tke and sdr values use the same conversion as the inlet turbulence conditions. Once iteration begins, each inlet applies its own local condition.
Coupled boundary states
Controller and compact-model states also need a first value:
- fan pressure rise starts at the zero-flow point of the supplied fan curve;
- flow-rate outlet pressure control uses zero relative pressure as its initial seed; and
- CTM face temperatures start at the reference temperature, from which the initial junction temperature is calculated.
These values are updated from the developing solution during the SIMPLE iterations.
Starting guesses during iteration
After initialization, each equation uses its field from the previous SIMPLE iteration as the starting guess for the next BiCGSTAB solve. Fields are therefore advanced from the current coupled state rather than reset to their original values.
The API does not currently accept a saved solution as a restart or warm-start field.
See also
- What the Vanellus solver does explains why SIMPLE iterations are not physical time steps.
- Boussinesq buoyancy and reference temperature explains how the temperature reference is selected.
- Residuals and linear-solver convergence explains the outer and inner iterations.
- Diagnose an instability gives the practical diagnostic workflow.
- API reference lists exact initialization fields and limits.