(615a) Flowing Complex Fluids, from Blood to the Buffer Layer
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Liaison Functions
William R. Schowalter Lecture
Wednesday, November 13, 2019 - 6:00pm to 7:00pm
The second part of this talk addresses one of the most puzzling and dramatic phenomena in non-Newtonian flow, the substantial reduction of turbulent energy dissipation (drag) that occurs when a small amount of a long-chain polymer is added to a liquid. If the Reynolds number is sufficiently low, a turbulent channel flow will laminarize as polymer concentration increases, but then become turbulent again at higher concentration. Direct simulations of flow in the latter regime, along with linear analyses performed by Beverley McKeonâs group, yield a surprising result: the turbulent fluctuations strongly resemble so-called Tollmien-Schlichting (TS) waves. Although these are found in Newtonian flows, they do not play a role in fully-developed Newtonian turbulence. In the polymeric case, however, polymer stresses suppress the normal turbulent structures while amplifying the TS modes. The emergence in viscoelastic flow of flow structures with Newtonian origin may shed light on the observed near-universality of the polymer drag reduction phenomenon with regard to polymer properties.