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Article overview
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Large-scale instability in a sheared nonhelical turbulence: formation of vortical structure | | T. Elperin
; I. Golubev
; N. Kleeorin
; I. Rogachevskii
; | | Date: |
20 Oct 2007 | | Abstract: | We study a large-scale instability in a sheared nonhelical turbulence that
causes generation of large-scale vorticity. Three types of the background
large-scale flows are considered, i.e., the Couette and Poiseuille flows in a
small-scale homogeneous turbulence, and the "log-linear" velocity shear in an
inhomogeneous turbulence. It is known that laminar plane Couette flow and
antisymmetric mode of laminar plane Poiseuille flow are stable with respect to
small perturbations for any Reynolds numbers. We demonstrate that in a
small-scale turbulence under certain conditions the large-scale Couette and
Poiseuille flows are unstable due to the large-scale instability. This
instability causes formation of large-scale vortical structures stretched along
the mean sheared velocity. The growth rate of the large-scale instability for
the "log-linear" velocity shear is much larger than that for the Couette and
Poiseuille background flows. We have found a turbulent analogue of the
Tollmien-Schlichting waves in a small-scale sheared turbulence. A mechanism of
excitation of turbulent Tollmien-Schlichting waves is associated with a
combined effect of the turbulent Reynolds stress-induced generation of
perturbations of the mean vorticity and the background sheared motions. These
waves can be excited even in a plane Couette flow imposed on a small-scale
turbulence when perturbations of mean velocity depend on three spatial
coordinates. The energy of these waves is supplied by the small-scale sheared
turbulence. | | Source: | arXiv, 0710.3862 | | Services: | Forum | Review | PDF | Favorites | |
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