[cnqin]

In Ansys_CFX-Pre_Users_Guide I found that "If you have chosen to solve a transport equation for the component, you can optionally enter a
value for Kinematic Diffusivity. If you do not set Kinematic Diffusivity, then the Bulk Viscosity value is used."

I simulated the miscible flow of CO2 and oil. Does kinematic diffusivity represent the diffusion coefficient of CO2 and oil?

If I do not set Kinematic Diffusivity, How does Bulk Viscosity value work?

[Opaque]

Originally Posted by cnqin

In Ansys_CFX-Pre_Users_Guide I found that "If you have chosen to solve a transport equation for the component, you can optionally enter a
value for Kinematic Diffusivity. If you do not set Kinematic Diffusivity, then the Bulk Viscosity value is used."

I simulated the miscible flow of CO2 and oil. Does kinematic diffusivity represent the diffusion coefficient of CO2 and oil?

If I do not set Kinematic Diffusivity, How does Bulk Viscosity value work?

Bulk viscosity value = Mixture Dynamic viscosity / Mixture density

If you have a binary mixture, say CO2 and oil only, the Kinematic Diffusivity represents the D_co2_oil. However, if you have more materials in the mixture, it represents the material diffusivity into the mixture.

If your flow is turbulent, that value is not meaningful unless you have strong mass fraction gradient in region of very low Re numbers

[cnqin]

Thank you for your answer.
But I have another problem. I set the wall of the multi-component flow to the free-slip wall, and the simulation cannot converge. Why?
My geometry model is a nano/microscale complex pore structure.

[ghorrocks]

It could be many reasons. It could be physical, which means the simulation as you have set it up is not solveable; or it could be numerical, which means it is not numerically stable enough to converge.

This FAQ is related to your question and might help: https://www.cfd-online.com/Wiki/Ansy...do_about_it.3F