
When displaying POLYFLOW results, it can be found that the postcalculated shear rate is not exactly vanishing along plane or axis of symmetry. Why? There is no actual remedy to this; but an explanation can be useful. The generalised shear rate is evaluated via a mean least square technique. It is applied to the components of the velocity gradient evaluated at integration points inside the elements. In order to prevent the occurrence of negative nodal values for the generalised shear rate, the calculation is performed at points located inside individual elements, and the result is then reported at the closest mesh node. Hence, instead of the possibly expected zero shear rate at a plane or axis of symmetry, one obtains a value calculated in its vicinity.

