I have a mechanism where air rises due to convective flows. In this simulation, nothing is driving the air except this. I understand that the Boussinesq approximation only works for small temperature differences. In this case, the temperature rise is 30k. The air has a thermal expansion coefficient of 0.0034k-1. Is this okay to use the approximation? My doubts exist because velocities exceed 1e5 m/s in the results. A quick calculation by hand tells me the velocities should be around 50 m/s. Is this a case of the temperature rise being too high to use the approximation or is there likely something else?

Steady-state calculation.

Heat is applied with solar race tracing and the DO radiation model (Temperature rise in the domain is as expected.

inlet - pressure inlet 0Pa , 293k

outlet - pressure outlet 0Pa, 293k

operating temperature - 293k

operating pressure - 1.2 kg/m3

viscosity - RNG k-epsilon

coupling - SIMPLE

gradient - Green-Gauss cell based

pressure - PRESTO!

All other methods - second order upwind

Any help would be appreciated.

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