Velocity singularity in natural convection
 

Hello everyone. Hope you are doing well.

I would like to understand the recurring phenomena that I'm facing while doing my final work.

When solving natural convection I'm getting some local anomalies in my velocity field. These anomalies usually appear in the middle of the domain from nowhere.

I did some tests with different geometries and solvers and it still happening. You can see it in the image below.

The case shown is a confined volume of ambient temperature air inside a metal box with a temperature Boundary Condition in one external face of the box. I'm solving with chtMultiRegionFoam.

I'm a beginner in CFD but I know you guys have lots of experience and can enlighten me with a possible cause/solution for this problem.

What can it be? Mesh resolution? fvSolutions/Schemes wrong?

Any points that you guys think I should check is appreciated.

Thanks in advance! :D

image is here: https://imgur.com/a/1lEVOPK