Inheritance of headbox flow vortices in fiber orientation

One of the most important factors affecting fiber orientation is turbulence. Turbulence is created by wall shear and by sudden expansions of the flow channels in the headbox. A lamella is one of the elements generating turbulence in the slice chamber by both of these phenomena. The use of lamellas leads to the formation of coherent flow structures, i.e., vortices. These vortices are believed to inherit in paper as fiber orientation structures. In this work this hypothesis was studied by generating vortices of different size in the paper machine headbox and analyzing both the flow and the orientation fields with a new pathline method. By determining vortex and orientation structure size distributions from pathline images, the inheritance of flow vortices in fiber orientation was quantitatively shown.