how to use INC_DENSITY_MODEL= BOUSSINESQ to solve the laminar convection in a cavity probelm.

[ztdepztdep]

INC_DENSITY_MODEL= BOUSSINESQ
INC_ENERGY_EQUATION= YES
FLUID_MODEL= CONSTANT_DENSITY
BODY_FORCE= NO
THERMAL_EXPANSION_COEFF= 0.003333333333
INC_TEMPERATURE_INIT= 300.0
INC_TEMPERATURE_REF= 300.0

I have set the above value, but i still cann't got a converged solution.
the rms(H) still ossicilating about -0.66.