Dynamics of energy condensation in two-dimensional turbulence.
We report a numerical study, supplemented by phenomenological explanations, of "energy condensation" in forced 2D turbulence in a biperiodic box. Condensation is a finite size effect which occurs after the standard inverse cascade reaches the size of the system. It leads to the emergence of a coherent vortex dipole. We show that the time growth of the dipole is self-similar, and it contains most of the injected energy, thus resulting in an energy spectrum which is markedly steeper than the standard k{-5/3} one. Once the coherent component is subtracted, however, the remaining fluctuations have a spectrum close to k{-1}. The fluctuations decay slowly as the coherent part grows.
Chertkov
M
M
Theoretical Division & Center for Nonlinear Studies, LANL, Los Alamos, NM 87545, USA.
Connaughton
C
C
Kolokolov
I
I
Lebedev
V
V
D003198:Computer Simulation