Dear professors,
Hello. I set up a model in the shape of a ring, and when I looked at the effect of the model, something strange happened. The heat in the model turned. I guess there’s something wrong with my initial temperature model Settings, but I don’t know how to correct it. As shown in the figure below, this is the result of a model of two adjacent time steps. I would appreciate it if anyone could help me!
Best wishes,
Lu
Dear Lu,
Both your inner and your outer boundary have free-slip conditions, which introduces a rotational nullspace in your model (i.e., what you see is that your whole solution can rotate by a large amount between two time steps). To fix that, you need to remove the nullspace through a parameter in the input file (just have a look at the subsection Nullspace removal and pick from one of the rotation/angular options; a common option is to have no net rotation, for example).
Best,
Juliane
Dear Juliane,
Thank you very much for your reply, now my problem has been solved! 
Best wishes,
Lu
