Viscosity Models

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

Attention: As of nanoFluidX 2022.2, several changes have occurred for viscosity modeling.
  • 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.
In order to make use of the Viscosity Models section, either 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.

Important: These changes are not backward compatible, so configuration files utilizing temperature or aeration-viscosity coupling and created for versions prior to 2022.2 will not be able to run in 2022.2 or later versions of nanoFluidX.

Commands

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
	}
}

Definitions

Command Contents SI Unit Example
viscosityModel_type Viscosity model choice which will be assigned to the respective fluid phase (viscosityModel_phase)
Options
  • FLUID_NEWTONIAN
  • FLUID_S_CROSS
  • FLUID_T_POLYNOMIAL
  • FLUID_T_SUTHERLAND
  • FLUID_T_POWER_LAW
Attention: Only one model can be selected per 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.

Default = 0.001

 [Pa.s]
viscosityModel_k Dimensionless coefficient k for the Cross model (see Viscosity Models for more information).

Default = 0.001
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 for more information).

Default = 0.0
viscosityModel_visc_0 Zero shear rate viscosity for the Cross model.

Default = 0.001

 [Pa.s]
viscosityModel_visc_inf Infinite shear rate viscosity for the Cross model.

Default = 0.001

 [Pa.s]
viscosityModel_c Coefficients for the temperature-viscosity polynomial model. This is a vector variable, comprising of 5 values defined in order of the polynomial.

Default = "0.001 0.0 0.0 0.0 0.0"

 [Pa.s, Pa.s/T, Pa.s/T2, Pa.s/T3, Pa.s/T4]
viscosityModel_temp_ref Base temperature of the Sutherland temperature-viscosity dependence model.

Default = 273.15

 [K]
viscosityModel_visc_ref Base viscosity of Sutherland temperature-viscosity dependence model.

Default = 0.00001716

 [Pa.s]
viscosityModel_sut Sutherland temperature (also known as Sutherland's coefficient).

Default = 110.4

 [K]