title: Physical mechanism of the two-dimensional inverse energy cascade.
abstract: We study the physical mechanisms of the two-dimensional inverse energy cascade using theory, numerics, and experiment. Kraichnan's prediction of a -5/3 spectrum with constant, negative energy flux is verified in our simulations of 2D Navier-Stokes equations. We observe a similar but shorter range of inverse cascade in laboratory experiments. Our theory predicts, and the data confirm, that inverse cascade results mainly from turbulent stress proportional to small-scale strain rotated by 45 degrees. This "skew-Newtonian" stress is explained by the elongation and thinning of small-scale vortices by large-scale strain which weakens their velocity and transfers their energy upscale.
authors.affiliation: Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Shiyi
authors.initials: S
authors.lastname: Chen
authors.forename: Robert E
authors.initials: RE
authors.lastname: Ecke
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Eyink
authors.forename: Michael
authors.initials: M
authors.lastname: Rivera
authors.forename: Minping
authors.initials: M
authors.lastname: Wan
authors.forename: Zuoli
authors.initials: Z
authors.lastname: Xiao