Ansys Polyflow automatically computes a stream function based on the velocity and the thickness fields.

In view of the mass conservation equation, Equation 18–4, a stream function can be defined by

(18–6)

where is the local value of the total thickness of the film. Then, obeys a Poisson equation:

(18–7)

The solution of Equation 18–7 is defined up to an arbitrary additive constant. Assigning one point where the value of the stream function is zero will determine this additive constant. By default, this is done at the node closest to the point .