Buoyancy force term in Fluent
 

I am modeling laser melting of a solid. Above the melting point, a Buoyancy force should act. Do I need to add this Buoyancy force separately through a UDF? I understand that gravity is there in the momentum equation. Above the melting point, a Buoyancy force is added. So, is it automatically added by Fluent or I need to add is using an external source term in the UDF?
I am using VOF with Solidification/Melting in FLUENT.

Why do we need to add a separate buoyancy force as a source term in the above melting point cases?

Hi, I am not sure. I am asking whether we need to add it separately using a UDF or FLUENT automatically adds it. I am confused because I haven't given coefficient of volumetric expansion in the properties section.