Ansys Employee

 Quick suggestions:

     1) On your velocity profile I see 2 lines perfectly aligned with the dump plane. What are those? some types of plates or numerical issues?

     2) Did you correctly resolve the wall area? A good wall resolution in the inlet is key to accurately predicts swirling flows

     3) Did you try different mesh resolution in general? This is key to predict circulation zones

     4) There is always some wiggle room on the swirl BC in numerical setup because translating experimental data from a swirl inlet to a simulation can be tricky. As Rob mentioned you should increase the swirl (change only the tangential velocity inlet component to nu modify the mass flow rate if you use a velocity BC). Remember that recirculation zones occur rapidly: a 5% change (+/-)  in tangential BC can lead to large velocity pattern changes (full recirculation/no recirculation)

Good luck!