title: Laminar superlayer at the turbulence boundary.
abstract: In this Letter we present results from particle tracking velocimetry and direct numerical simulation that are congruent with the existence of a laminar superlayer, as proposed in the pioneering work of Corrsin and Kistler (NACA, Technical Report No. 1244, 1955). We find that the local superlayer velocity is dominated by a viscous component and its magnitude is comparable to the characteristic velocity of the smallest scales of motion. This slow viscous process involves a large surface area so that the global rate of turbulence spreading is set by the largest scales of motion. These findings are important for a better understanding of mixing of mass and momentum in a variety of flows where thin layers of shear exist. Examples are boundary layers, clouds, planetary atmospheres, and oceans.
authors.affiliation: Max Planck Institute for Dynamics and Self-Organisation, Bunsenstrasse 10, 37073 Göttingen, Germany. markus.holzner@ds.mpg.de
authors.forename: M
authors.initials: M
authors.lastname: Holzner
authors.forename: B
authors.initials: B
authors.lastname: Lüthi