Buoyancy models
 

1.When I choose a buoyancy model , should the thermal expansivity values be specified to the component or the medium in which it is flowing
2. I have a compressible gas flowing in air & i am able to specify density diff/boussinesq & thermal expansivity values for air , but I am not able to enter thermal expansivity values /choose boussinesq model for gas. Is there any explanation for it.

3.Should I enter a specified solver options while doing compressible flow?
where can I get information about the solver opitons , Is there any document for it. I would like to know what happens when I choose different solver options in CFX.