Dear Edward Jenks

first, from my point of view the Boussinesq approximation should work without any problem in your case. The temperature difference you have is definitely ok, the thermal expansion coefficient is an order higher than the one I am using, but in my case, the temperature difference is much higher, so the multiple of both should result in the same magnitude. You wrote that your operating pressure - 1.2 kg/m^3, I assume this is a typo and you mean operating density.

Check this link from the manual to see if your numerical setup is correct:

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v211/en/flu_ug/flu_ug_Operating_Conditions.html?q=Boussinesq%20approximation

Here is more information about the theory and limitations of the approach:

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v211/en/flu_th/flu_th_sec_hxfer_buoy.html

Basically, the Boussinesq approximation is valid when the product of the thermal expansion coefficient and the temperature difference is below 1.

You need to provide more information about your model in order to get some help. However, I would initially suggest improving the mesh, since in such calculations a coarse mesh will lead to too high velocities, and that is what you experience.

Best of luck!

Antoni Artinov

Hi Edward,

Are you seeing any error or warning messages during simulations? Temperature limitation warning or viscosity limitation, these could trigger some such velocity hikes ?

Regards,

Rajesh.

Dear Edward Jenks

I fully agree with the detail and good answer given by Mr. Antoni Artinov.

Regards