For a generalized Newtonian flow, Ansys Polyflow computes the inflow from your specified volumetric or mass flow rate in two ways using a fully developed method and/or using a constant normal force. You can either explicitly specify a method or allow Ansys Polyflow choose the best method.
Fully developed method: In this method, Ansys Polyflow solves a fully developed flow problem. Here it is assumed that all derivatives normal to the inlet are zero, except the pressure gradient, which is assumed to be constant. In 2D, Ansys Polyflow solves a 1D problem along the segment, calculating the velocity profile at every node of the entry section, assuming fully developed flow. Similarly, in 3D, Ansys Polyflow calculates a fully developed channel flow problem in 2D, assigning the nodal velocities in the entry section. Ansys Polyflow will then impose the computed velocity profile as the prescribed velocity.
Constant normal force method: In this method, the normal force is prescribed (assumed constant on the boundary section), with its value being required to obtain the prescribed flow rate. The value of the pressure is calculated by Ansys Polyflow and the velocity components are not prescribed.
The two methods differ mainly for short inlet sections. In this case, assuming that the normal force (mostly the pressure) is constant, the fully developed method might be a better option if the inlet section is connected to a large reservoir. In the presence of significant gravitational forces acting tangent to the inlet, the constant normal force method does not result in a fully developed flow condition.
If Ansys Polyflow is allowed to choose the best method for you, it will select the fully developed method. For inverse extrusion problems where the inlet is part of the constant section (parallel dies), however, the constant normal force method will usually be chosen.