Ansys Employee

Hello Jason,

Ansys Fluent provides several options for definition of the fluid viscosity:

  • constant viscosity

  • temperature-dependent and/or composition-dependent viscosity

  • kinetic theory

  • non-Newtonian viscosity

  • user-defined function

Each of these input options and the governing physical models are detailed in this section. (User-defined functions are described in the Fluent Customization Manual). In all cases, define the Viscosity in the Create/Edit Materials Dialog Box.

 Setup →   Materials

Viscosities are input as dynamic viscosity () in units of kg/m-s in SI units or /ft-s in British units. Ansys Fluent does not ask for input of the kinematic viscosity ().

Please refer 8.4. Viscosity (ansys.com)

There are 2 types of viscosities - dynamic and kinematic 

Absolute viscosity - coefficient of absolute viscosity - is a measure of internal resistance. Dynamic (absolute) viscosity is the tangential force per unit area required to move one horizontal plane with respect to an other plane - at an unit velocity - when maintaining an unit distance apart in the fluid.

Kinematic viscosity is the ratio of - absolute (or dynamic) viscosity to density - a quantity in which no force is involved. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid with the fluid mass density like

ν = μ / ρ                  

kinematic viscosity= dynamic viscosity/ density.

This should solve your misunderstanding.


Chaitanya Natraj