Rob, this is the BCs:
Red lines are wall.
Left side: inlet (velocity-inlet)
Right side: outlet (pressure-outlet)

REAL CASE: After the injection orifice, the top and bottom walls are really distant from the injection point;
SIMULATION: V.C. of 1 injection point, exclusively to measure the Distance vs Inlet Velocity (mass flow is constant - define the best orifice area);

However, if i haven't extended the wall, shouldn't the air flow be symmetric, as the dimensions are?

Thanks so far, Rob.