Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Analysis of the forward and backward in time pair-separation PDFs for
  inertial particles in isotropic turbulence   In this paper we investigate, using theory and Direct Numerical Simulations
(DNS), the Forward In Time (FIT) and Backward In Time (BIT) Probability Density
Functions (PDFs) of the separation of inertial particle-pairs in isotropic
turbulence. In agreement with our earlier study (Bragg et al., Phys. Fluids 28,
013305 (2016)), where we compared the FIT and BIT mean-square separations, we
find that inertial particles separate much faster BIT than FIT, with the
strength of the irreversibility depending upon the final/initial separation of
the particle-pair and their Stokes number $St$. However, we also find that the
irreversibility shows up in subtle ways in the behavior of the full PDF that it
does not in the mean-square separation. In the theory, we derive new
predictions, including a prediction for the BIT/FIT PDF for ${St\geq O(1)}$,
and for final/initial separations in the dissipation regime. The prediction
shows how caustics in the particle relative velocities in the dissipation range
affect the scaling of the pair-separation PDF, leading to a PDF with an
algebraically decaying tail. The predicted functional behavior of the PDFs is
universal, in that it does not depend upon the level of intermittency in the
underlying turbulence. We also analyze the pair-separation PDFs for fluid
particles at short-times, and construct theoretical predictions using the
multifractal formalism to describe the fluid relative velocity distributions.
The theoretical and numerical results both suggest that the extreme events in
the inertial particle-pair dispersion at the small-scales are dominated by
their non-local interaction with the turbulent velocity field, rather than due
to the strong dissipation range intermittency of the turbulence itself...

7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
24
The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
13
The categories of this paper are: quant-ph
33
The categories of this paper are: plasm-ph