For a viscoelastic flow, Ansys Polyflow computes a fully developed velocity profile from your specified volumetric (or mass) flow rate and imposes it as a boundary condition for the flow problem. The fully developed stress profile is also computed and imposed as a boundary condition for the (hyperbolic) constitutive equation. Ansys Polyflow solves a finite-element problem along the boundary section to calculate the velocity and viscoelastic stresses at every node of the inlet section.

The validity of the inflow condition requires the computational domain to be built in such a way that the basic assumptions of fully developed Poiseuille flow are satisfied. This is usually ensured when the inlet section is long enough. For axisymmetric geometries, the inlet section must be perpendicular to the axial direction. You can therefore consider that such a boundary condition replaces a long channel upstream of the inlet section.