"Internal" scale and large scale vortex formation
Abstract
Experimental evidence for intermittency - the extremely alternating inhomogeneous distribution of small-scale turbulence - proves that this phenomenon is related to spontaneous generation of new non-trivial internal scales in a turbulent flow. The new characteristic (internal) scales differ parametrically from the scale of an external force driving turbulence. This parametrical difference has allowed us to develop a new approach to the problem of intermittency. The discrete set of all possible non-trivial characteristic scales has been found, L_{int}=r_0/γ^{1/(n+1)}, n=1,2,dots and the spectra corresponding to turbulent fluctuations at these scales have been established, E_k∼1/k^{1-2Δ (n)}, where Δ(n) = -(n + 1)/(n + 2), γ=f_0τ_0^2/r_0 is the dimensionless parameter of the theory, f_0, τ_0 and r_0 are the amplitude, the correlation time and the correlation length of a force driving turbulence. The generation of new scales in some points of a turbulent flow implies spontaneous development of vortexes at these points. For γ≪1 it is shown that the largest scale vortexes are associated with the 7/3- spectrum (or n=1) and governed by the flux of helicity through the spectrum. Refs 4.
- Publication:
-
Magnetohydrodynamics
- Pub Date:
- June 2001
- Bibcode:
- 2001MHD....37...23G