air ideal gas in CFX Pre
Hi all,
I have a small question about air ideal gas in CFX Pre. Whether or not air ideal gas considers the properties of air e.g. convection, diffusion/dispersion and radiation etc.? If not, how should we set those properties in CFX Pre step by step in detail? Many thanks in advance! Br. wang 
Air ideal gas can support all those physics. But you have to set the models up (eg buoyancy, something to diffuse and a radiation model) to use it.

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Many thanks! I can find and define buoyancy model and radiation model. But I can't find diffuse and convection (only exist buoyancy model?) model. Please show me where are they or how to define them: diffuse and convection model for ideal air. Many thanks in advance! 
There are several types of buoyancy model. The first is to use a Boussinesq buoyancy model in an incompressible fluid  this is simplest and least accurate. A more accurate approach is to use an ideal gas with heat transer and let the ideal gas equation take care of the density difference. You will need to define a gravity vector for both of these approaches.
The convection model is built in  if the fluid is flowing it is convecting. 
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There is no Boussinesq buoyancy model in my CFX/Pre, or I cant find it. I dont know why? In my CFX pre DomainBasic settings, Buoyancy ModelOption only exists No Buoyant and Buoyant. I used Buoyant, I set already Gravity Vector and Buoy. Ref. Density **kg/m3. Is this Type 2nd approach as you said? And where is Diffusion model? How to define it in CfxPre? Is the diffusion model is also built in  if the fluid is flowing it is diffusing? Many thanks in advance! 
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If you mean of momentum then the viscosity does this. If you mean of heat then thermal conductivity does this. If you mean of another scalar the diffusivity of the scalar does this. 
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1) Do you mean to enable the Thermal Model in Domain/Fluid Models in CFXPre? But I only find Heat Transfer option in Domain/Fluid Models, there is no thermal model. Maybe since I selected Continuous Fluid not incompressible fluid, so I can't find a boussinesq buoyancy model? 2)I used CO2 as Ideal Air's additional variable, for Kinematic Diffusivity option, whether I should set Diffusivity Coefficient as 1.64*10^5 m2/s here for CO2Air? Many thanks in advance! 
Sounds like you need more specific comments rather than general comments.
Can you describe what you are trying to do, and the results you hope to obtain and we can comment on the best way to achieve it? 
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Besides, for Kinematic Diffusivity option of CO2 as additional variable, whether I should set Diffusivity Coefficient as 1.64*10^5 m2/s here for CO2Air? Or other value I should define here? For buoyancy model, Do you mean to enable the Thermal Model in Domain/Fluid Models in CFXPre? But I only find Heat Transfer option in Domain/Fluid Models, there is no thermal model. Maybe since I selected Continuous Fluid for Ideal Air Gas not incompressible fluid, so I can't find a boussinesq buoyancy model? Many thanks in advance! 
An additional variable has convection and diffusion (if you choose the appropriate option). You could link it to a source term for bouyancy but if you want CO2 to affect buoyancy I would instead use a multi component mixture which will then allow for the different material properties between air and CO2.

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