If you reduce the UR factor the model will be more stable as the solution changes by a smaller amount. If you increase it the solution may jump around before stabilising. Depending on how stable the physics are (ie how well attached the flame is) this could be just enough to give a different solution: the larger UR may miss the flame detaching in this case. Try increasing & decreasing the flow by 5%. The next step will be to refine the mesh and study the near burner flow in more detail.https://forum.ansys.com/discussion/comment/97773#Comment_97773

nI would like to add that if the solution do not converge for meshing or other problems , the relaxtion factors don't help you. But sometimes you can reduce the step to hel the simulation to convergence.nRegards,Federicon