THEORY OF TWO-DIMENSIONAL ANISOTROPIC TURBULENCE.

Abstract

Utilizing an abridged version of the test field model, the relaxation of two-dimensional homogeneous turbulence back to its isotropic state is examined. It is found that the relaxation back to isotropy is very non-local in wavenumber space, a result seemingly in counter-distinction to three-dimensional turbulence for which the relaxation is supposedly local. The difference is explained by the importance in two-dimensional flows of direct straining of small scales by large scales. Some preliminary direct spectral numerical simulation data in support of these ideas are also presented. The implications of the findings for subgrid-scale parameterization are discussed, and a formalism for describing the evolution of the large scales with parameterized treatment of the small scale is sketched.