[lovegne]

i am getting negative mass flow rate at outlet of my flow domain. what does that mean ?

[flotus1]

Summoning all my psychic power I sense that this is a Fluent or CFX question despite the hint "do not post fluent questions here".
In this case, a negative mass flow rate indicates that flow velocity vector and surface normal vector are pointing in opposite directions. In these programs, surface normal vectors point towards the computational domain by default.