Theory
The incompressible solver works with the kinematic pressure ; the density converts it to pascal for every reported pressure and turns a mass flow into a velocity. It is computed from equation (1). A typed value replaces it for the run: the field then carries a "user" badge, stops following the temperature and pressure, and offers "reset to computed"; the report marks it "manual override".
The program records in the run folder the density each run was built with, so the results of that run are always converted with it, even when the material settings change later.
Equations
| where | meaning | unit |
|---|---|---|
| Density | kg/m³ | |
| Ambient pressure | Pa | |
| 0 (density reference ambient) or half the previous static pressure drop (mean) | Pa | |
| Molar mass of the gas | kg/kmol | |
| Universal gas constant, 8314.47 | J/(kmol K) | |
| Material temperature | K |
Default and rule
- Default
- computed from temperature and ambient pressure (ideal gas)Computed by the program
- Rule
Computed (the field is empty in the case file). Air at 20 °C and 101 325 Pa: 1.204 kg/m³.
- Source
The ideal-gas law, equation (1). The 2 % warning threshold is the program's own choice; it has no published basis.
Valid range > 0; warning when more than 2 % off the computed value
Values
Above 0.
Manual value
A typed density more than 2 % away from the computed one is warned about: it no longer agrees with the temperature and pressure of the case.
Compressible solver
Ignored: the compressible solver computes the density from the solved pressure and temperature.