Ansys Employee

Please post some images. 

Re back flow, you need to understand the flow to see why it's occuring, and then whether it's effecting the result and/or area of interest. 

Residuals may never converge for this type of problem. That's why we use monitor points (note POINT not area average on a surface). Have a look at the tutorials under Help and some of the courses under Learning (book icon left side of this page).