Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Multi-scale model of gradient evolution in turbulent flows   A multi-scale model for the evolution of the velocity gradient tensor in
fully developed turbulence is proposed. The model is based on a coupling
between a ``Restricted Euler'' dynamics [{\it P. Vieillefosse, Physica A, {\bf
14}, 150 (1984)}] which describes gradient self-stretching, and a deterministic
cascade model which allows for energy exchange between different scales. We
show that inclusion of the cascade process is sufficient to regularize the
well-known finite time singularity of the Restricted Euler dynamics. At the
same time, the model retains topological and geometrical features of real
turbulent flows: these include the alignment between vorticity and the
intermediate eigenvector of the strain-rate tensor and the typical teardrop
shape of the joint probability density between the two invariants, $R-Q$, of
the gradient tensor. The model also possesses skewed, non-Gaussian longitudinal
gradient fluctuations and the correct scaling of energy dissipation as a
function of Reynolds number. Derivative flatness coefficients are in good
agreement with experimental data.

19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
13
The categories of this paper are: quant-ph
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
24
The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph