Generation of Streamwise Vortices in a Slice Knife Model: Can Streaks be Generated at the Slice Exit?, 2002 Fall Technical Conference

The focus of this investigation is determining how and where headboxes generate streamwise vortices (i.e. MD streaks). This specific study isolates on the effects of exit geometry, in particular the slice knife, on streak formation. Highly resolved digital particle image velocimetry (DPIV) was used to study initially laminar steady flow past a 2D channel terminated by a partial (up to 50% of the channel height) blockage. Experiments were conducted in a water tunnel using slice geometries and conditions similar to actual headboxes.

Mean and instantaneous DPIV vector fields clearly show an unsteady spanwise (CD) vortex forms in the corner formed by the top nozzle wall and knife. More importantly, turbulent streamwise vortices are also generated. The size and spacing of the streamwise vortices closely corresponds to streak spacings found in paper. The relation between spanwise and streamwise vortices were examined in the context of understanding the origins of the streamwise vortices.