issue in mass flow rate graph
 

hi friends,

Here I have a strange issue,
I' modeling an axisymmetric 2 phases flow in a tube,
at the end of simulation, I plot the mass flow rate graph some section across the radius, but there is an issue,
As it's clear in the pictures, mass flow rate for each phase near the axis is zero!
I guess it's logical to mass flow be Max. at the axis, so I think it's irrational!
what do you think!? you think these graphs wrong too!!?