These instantaneous snap shots show flow velocity (mean flow is left to right, with velocity increasing from black to yellow) in a plane near and parallel to the wall, where eddy formation is intense. Comparing viscous to viscoelastic flow shows that the polymer increases space between the streaks and length of the high-velocity structures.
"There's an experimentally developed empirical relationship," says Beris, "correlating drag reduction to enhancement of the space between the streaky structures. Our results verify that relationship to within five percent."
At higher L value, which represents increased polymer resistance to extension of the flow, the streaks show more coherence, like stripes extending through the flow. The increased structure, a more laminar quality of the flow, corresponds to lowered turbulent drag.
![[image]](GRAPHIC_1.gif)
![[image]](GRAPHIC_2.gif)
![[image]](GRAPHIC_3.gif)
