Independence between friction and velocity distribution in fluids subjected to severe shearing and confinement.

Friction reduction is more than ever a key point in saving natural resources and energy, and the question of how to achieve this concerns first and foremost every lubricated system. Among the observed phenomena related to lubricated friction, limiting shear stress (LSS) appears to be one of the most challenging to explain, since its origin is still uncertain. Various scenarios have been proposed involving a transition to a glassy state under high pressure, shear banding, shear localization, or even the occurrence of slip at the solid-liquid interface, none of which have proven conclusive.

Flow enhancement due to elastic turbulence in channel flows of shear thinning fluids.

We explore the flow of highly shear thinning polymer solutions in straight geometry. The strong variations of the normal forces close to the wall give rise to an elastic instability. We evidence a periodic motion close the onset of the instability, which then evolves towards a turbulentlike flow at higher flow rates.