I simulate the extrusion of a polymer (pp) through a nozzleish solid and the extrudate doesnt show any die swell. On contrary, the extrudate is smaller in size than the die. I study mechanical engineering(gonna start my 3rd year 2 weeks later) so I dont even know much about polymers and their extrusion process. Is it possible?

Is it because the nozzle increases velocity and decreases pressure so to balance flow rate from V.A=Q(t) Area decreases so extrudate gets smaller or do my simulation parameters have something to do with it?

I used power law( exponent with evolution scheme) . Picard iterations. λ = 1. If anything needed to identify the problem I can provide more info

Thanks for reading!