# Viscosity Models

This section describes the parameters for properly enabling various viscosity models.

- The aeration-viscosity coupling has been deprecated as practical use of these models was not viable (need for model calibration, lack of manufacturer specifications).
- The existing temperature-viscosity coupling model commands have changed format and are now incorporated into the new viscosity models section.
- Cross model non-Newtonian fluids are now available in nanoFluidX, also conveniently associated with the viscosity model section.

`varvisc_temperature`or

`varvisc_non_Newtonian`parameters in the Simulation Parameters section must be activated (set to true).

- If these simulation parameters are kept false, then the standard dynamic viscosity definition in the Phases Parameters takes precedence.
- If either
`varvisc_temperature`or`varvisc_non_Newtonian`are enabled (set to true), and a fluid phase is missed in the Viscosity Models section - the missed fluid will be assumed Newtonian and the standard dynamic viscosity definition from the Phase Parameters is assumed. It is best practice that if either`varvisc_temperature`or`varvisc_non_Newtonian`are enabled, you proceed using the Viscosity Models section for definition of all phase viscosity models.

For more information about viscosity models, refer to Viscosity Models in the Theory Manual.

```
viscosityModels
{
viscosityModel
{
viscosityModel_type FLUID_NEWTONIAN
viscosityModel_phase 1
viscosityModel_visc 1e-3
}
viscosityModel
{
viscosityModel_type FLUID_S_CROSS
viscosityModel_phase 3
viscosityModel_k 1.0
viscosityModel_n 0
viscosityModel_visc_0 1e-3
viscosityModel_visc_inf 1e-3
}
viscosityModel
{
viscosityModel_type FLUID_T_POLYNOMIAL
viscosityModel_phase 4
viscosityModel_c "1e-3 0.0 0.0 0.0 0.0"
}
viscosityModel
{
viscosityModel_type FLUID_T_SUTHERLAND
viscosityModel_phase 5
viscosityModel_visc_ref 1.716e-5
viscosityModel_temp_ref 273.15
viscosityModel_temp_sut 110.4
}
viscosityModel
{
viscosityModel_type FLUID_T_POWER_LAW
viscosityModel_phase 6
viscosityModel_visc_ref 1e-3
viscosityModel_temp_ref 273.15
viscosityModel_n 0
}
}
```

`viscosityModel_type`- Viscosity model choice which will be assigned to the respective fluid
phase (
`viscosityModel_phase`) `viscosityModel_phase`- Phase ID of the fluid phase which is affected by the selected model choice.
`viscosityModel_visc`- Dynamic viscosity when using the Newtonian fluid model.

`viscosityModel_k`- Dimensionless coefficient k for the Cross model (see Viscosity Models in the Theory Manual for more information).

`viscosityModel_n`- Serves as a dimensionless power exponent in the Cross model for non-Newtonian viscosity and Power Law temperature dependence model (see Viscosity Models in the Theory Manual for more information).
`viscosityModel_visc_0`- Zero shear rate viscosity for the Cross model.

`viscosityModel_visc_inf`- Infinite shear rate viscosity for the Cross model.

`viscosityModel_c`- Coefficients for the temperature-viscosity polynomial model. This is a vector variable, comprising of 5 values defined in order of the polynomial.
`viscosityModel_temp_ref`- Base temperature of the Sutherland temperature-viscosity dependence model.
`viscosityModel_visc_ref`- Base viscosity of Sutherland temperature-viscosity dependence model.
`viscosityModel_sut`- Sutherland temperature (also known as Sutherland's coefficient).