IFIBA   22255
INSTITUTO DE FISICA DE BUENOS AIRES
Unidad Ejecutora - UE
artículos
Título:
Large scale effects on the decay of rotating helical and non-helical turbulence
Autor/es:
T. TEITELBAUM; P.D. MININNI
Revista:
PHYSICA SCRIPTA - (Print)
Editorial:
IOP PUBLISHING LTD
Referencias:
Año: 2010 vol. 142 p. 140031 - 140039
ISSN:
0031-8949
Resumen:
Turbulent
mixing in geophysics is often affected by the presence of rotation,
which renders the flow anisotropic at large scales. Helicity
(correlation between the velocity and its curl) has relevance for
atmospheric and astrophysical flows and can also affect mixing. In this
paper, decaying three-dimensional (3D) turbulence is studied via direct
numerical simulations (DNS) for an isotropic non-rotating flow and for
rotating flows with and without helicity. We analyze the cases of
moderate Rossby number and large Reynolds number, focusing on the
behavior of the energy spectrum at large scales and studying its effect
on the time evolution of the energy and integral scales for E(k)~k4 initial conditions. In the non-rotating case, we observe the classical energy decay rate t−10/7 and a growth of the integral length proportional to t2/7
in agreement with the prediction obtained assuming conservation of the
Loitsyanski integral. In the presence of rotation we observe a
decoupling in the decay of the modes perpendicular to the rotation axis
from the remaining 3D modes. These slow modes show a behavior similar
to that found in two-dimensional (2D) turbulence, whereas the 3D modes
decay as in the isotropic case. We phenomenologically explain the decay
considering integral conserved quantities that depend on the
large-scale anisotropic spectrum. The decoupling of modes is also
observed for a flow with a net amount of helicity. In this case, the 3D
modes decay as an isotropic fluid with a constant, constrained integral
length and the 2D modes decay as a constrained rotating fluid with
maximum helicity.