# Viscosity-temperature Coupling Parameters

This section describes the parameters for properly modelling viscosity-temperature coupling.

```
viscTempModels
{
viscTemp_model
{
phase_affected 1
viscTemp_model POLYNOMIAL
poly_coeffs1 0.0
poly_coeffs2 0.0
poly_coeffs3 0.0
poly_coeffs4 0.0
poly_coeffs5 0.0
}
viscTemp_model
{
phase_affected 1
viscTemp_model SUTHERLAND
sutherland_refVisc 0.1
sutherland_refTemp 273.15
sutherland_coefficient 12.01
}
viscTemp_model
{
phase_affected 1
viscTemp_model POWER_LAW
power_refVisc 1.716e-5
power_refTemp 273.15
power_exponent 0.666
}
}
```

`phase_affected`- Similar to the
`phase_motion`command, this option tells you which phase is affected by this viscosity-temperature dependence model. `viscTemp_model`- Model according to which the viscosity will be calculated as a function of temperature.

Each viscosity-temperature has its own set of characteristic parameters. For polynomial model those are the five polynomial coefficients, for Sutherland model those are reference viscosity, reference temperature and the Sutherland coefficient. Finally, the power law has reference viscosity, reference temperature and the exponent. For more details about the models see Viscosity-temperature dependence models.

`poly_coeffs1`,`poly_coeffs2`,`poly_coeffs3`,`poly_coeffs4`, and`poly_coeffs5`- Polynomial coefficients for the polynomial viscosity-temperature model.
`sutherland_refVisc`- Sutherland reference viscosity.
`sutherland_refTemp`- Sutherland reference temperature
`sutherland_coefficient`- Sutherland coefficient
`power_refVisc`- Power law reference viscosity
`power_refTemp`- Power law reference temperature
`power_coefficient`- Power law exponent

`viscTempCoupling`capability, all the FLUID phases must have their viscosities defined by one of the three

`viscTempCoupling`models. It is not possible to have one FLUID phase with constant viscosity and others with variable viscosity.