backflow in a jet simulation
 

I created a structured domain with 'block' method in ICEM and then I imported the mesh into CFX11 to run a jet simulation. At the left side, i got two inlets, one is the major for jet (v1=12.8 m/s), the other one is the whole left side except for that jet (v2=V1*2%). I did this for avoiding the backflow since the jet flow will impinge on an airfoil and some of them will be reflected. However, though i've already set v2=v1*8%, there's still backflow and make an error to the simulation. I tried an unstructed mesh by using Ansys Workbench and the same setup in CFX (v2=v1*2%), the simulation's successful. Does anyone happen to meet this sort of situation? Please give me some hints. Cheers.