In manual, Boussinesq approximation is valid when beta*(T-T_0) << 1 and should not be used if the temperature differences are large.

@ beta : thermal expansion coefficient.

So, What model can I use for buoyancy-effected flow (ex, mixed convection with property variations) except Boussinesq approximation in FLUENT?

Hi,

If the pressure variations are small enough, you could use incompressible ideal gas model. It should be used when the flow is fully incompressible, then density is a function of temperature only, where for ideal gas model it is a function of pressure and temperature. Therefore you should specify the operating pressure for this model.

Regards emre