Theory
The incompressible solver uses the kinematic viscosity . Sutherland's law, equation (1), gives the viscosity of a gas as a function of the temperature only, with no pressure dependence; it rises with temperature (air: 18.2 µPa s at 20 °C, about 41 µPa s at 700 °C). The constants are those of Sutherland coefficient As and Sutherland temperature Ts, the same for air and exhaust gas.
A typed value replaces the computed one for the run, with a "user" badge, "reset to computed" and the report row "manual override".
Equations
| where | meaning | unit |
|---|---|---|
| Dynamic viscosity | Pa s | |
| Sutherland coefficient, 1.458e-6 by default | kg/(m s K^0.5) | |
| Sutherland temperature, 110.4 by default | K | |
| Material temperature | K | |
| Kinematic viscosity the solver uses | m²/s | |
| Density | kg/m³ |
Default and rule
- Default
- computed from the temperature (Sutherland's law)Computed by the program
- Rule
Computed (the field is empty in the case file). Air at 20 °C: 1.81e-5 Pa s.
- Source
Sutherland's law (Sutherland, 1893). 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 viscosity more than 2 % away from the computed one is warned about.
Compressible solver
Ignored: the compressible solver applies Sutherland's law to the local temperature.