## Fluids

#### Granular Viscosity & Material Viscosity in Mixture Model

• ZiaulH20
Subscriber

Dear Respected Individuals,

In Mixture model while defining a particulate phase as a Granular Phase ( in the 'Phases' Section in Mixture Model), a granular viscosity is required. Also, while defining a particulate material (in the material section) which is to be assigned as the granular phase, a Viscosity value is required as shown in the pictures below. I would like to know what is the difference between these two viscosities and how they are used in solving the governing equations. Thanks.

'Granular Viscosity' in Phases Section:

• YasserSelima
Subscriber
I am not sure why is Fluent requesting two values of the same material viscosity. But I have read in one of the topics in this forum that the material panel viscosity for 'solid material' is not the one used in calculation and the one in phase panel is the one used. nBut why don't you set both of them with the same value?n
• ZiaulH20
Subscriber
Noted on the above.nI read in theory guide that the solid shear viscosity is the sum of collisional, kinetic and frictional viscosity. For my case frictional viscosity is negligible. So the granular viscosity specifies the sum of kinetic and collisional viscosity. nFor my case, the particle viscosity is a function of particle volume fraction and fluid viscosity. So I have prepared a udf to calculate particle viscosity for the solid particle in 'material panel'. So should be okay to use the same udf in the phase panel in granular viscosity input right?nIn user guide, it says that the udf for granular viscosity must include the kinetic portion and the collisional portion of the viscosity in the value it returns.nThanksnn
• YasserSelima
Subscriber
I can't see a problem in using the UDF in both locations. Hopefully Fluent doesn't see an issue as well.nReturn only the sum of terms applicable to your case.n