sry for my late answer.

My case is a cd-nozzle with two different pressure-inlets, multiple phases, and one outlet. There is one hot and one cooling gas.

I am looking for such a study in which region along the line, created in the divergent part of the nozzle, the massflow-density is high/low because the massflow at the cooling-inlet is fluctuating between 7 g/s and 10 g/s per Iteration. It's a stationary simulation. I think this is good done with massflow-density. The Problem is the possibiltiy that characteristcs along the subsonic-boundary-layer thickness can reach the cooling-inlet and causes this fluctuation. The hot gas has a masslflow at 307... g/s (picture below). So in Fluent we can report the massflow but we can't see in which direction the mass is flowing. Am I wrong?

But I used the simple formula density*velocity (valid for stationary mesh/flow) along the line. This is equal to the massflow-density. But in Fluent there is only velocity-magnitude and axial/radial-velocity. So I can use the components of the velocity to study I which direction the mass is flowing or make a simple vector plot.