Settings to take Buoyancy into Account for Natural Convection

What are the settings to take buoyancy into account for natural convection?

One example of buoyancy is when a static fluid is heated by heat transfer from a solid surface, the density of the fluid is reduced; becoming lighter than the surrounding cold fluid flow. Buoyancy is caused by the density gradient due to a change in temperature of the fluid. Certain settings can be enabled in Fluent software to account for this phenomenon.

These settings are described in the PDF file shown below.