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Graduate Aeronautical Laboratories
Caltech
Abstract-
Vortex-based models of small-scale turbulent scalar transport are
considered.
A two-time asymptotic solution to the scalar advection-diffusion equation,
with
an azimuthal swirling velocity field provided by a stretched spiral vortex,
is used to
calculate
the spectrum of a passive scalar mixed by the vortex. Isotropy is not
assumed. The
scalar spectrum
is the sum of two power laws, a k-1 Batchelor spectrum for
wavenumbers
up to the
inverse Batchelor scale and a k-5/3 Obukov-Corrsin spectrum for
wavenumbers
less than the inverse Kolmogorov scale. The vortex-based model is also used
to obtain
a
tensor-gradient expression for the local subgrid flux of a passive scalar,
suitable
for use in the
large-eddy simulation of turbulent flows. Model predictions are compared
both with
experiment and with results obtained from the direct numerical simulation of
turbulent mixing.
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