I am trying to do some experiment but got the following message all the time....Boundary condition: Argon outlet; Inlet flow/outlet flow = 0,989....or  1,01 approximately. And consequently When I do trajectories..argon goes back. What's wrong and how can I eliminate the problem. ?? out let I had Statistic Pressure 101355 Ps...as it was given..and Inlet..was volume rate...