As an iterative solver, AFT xStream needs initial guesses to start the AFT Arrow Steady Solution process. xStream will make default initial guesses automatically. On occasion the AFT xStream guesses are far away from reality. For some models providing an initial guess for all the pipe flow rates in the system can help the model converge for the steady state.

User-defined initial guesses can be as simple as selecting all the pipes and initializing all of them to 1 lbm/sec, even though some operate at 0.1 lbm/sec and others at 10 lbm/sec. Note that initial guesses that are too far from the final solution can also interfere further with convergence.