Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Review of Physics-based and Data-driven Multiscale Simulation Methods
  for Computational Fluid Dynamics and Nuclear Thermal Hydraulics   Modeling of fluid flows requires corresponding adequate and effective
approaches that would account for multiscale nature of the considered physics.
Despite the tremendous growth of computational power in the past decades,
modeling of fluid flows at engineering and system scales with a direct
resolution of all scales is still infeasibly computationally expensive. As a
result, several different physics-based methodologies were historically
suggested in an attempt to "bridge" the existing scaling gaps. In this paper,
the origin of the scaling gaps in computational fluid dynamics and thermal
hydraulics (with an emphasis on engineering scale applications) is discussed.
The discussion is supplemented by a review, classification, and discussion of
the physics-based multiscale modeling approaches. The classification is based
on the existing in literature ones and distinguishes serial and concurrent
approaches (based on the information flow between micro- and macro-models) with
their variations. Possible applications of the data-driven (machine learning
and statistics-based) methods for enabling and / or improving multiscale
modeling (bridging the scaling gaps) are reviewed. The introduced
classification distinguishes error correction (hybrid) models; closure modeling
(turbulence models, two-phase and thermal fluid closures); and approaches aimed
at the facilitation of the concurrent physics-based multiscale modeling
approaches. A comprehensive review of data-driven approaches for turbulence
modeling is performed.

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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
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The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
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The categories of this paper are: nlin
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys