Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Towards Direct Numerical Simulation of a 5x5 Rod Bundle   Rod bundle flows are prevalent in nuclear engineering for both light water
reactors (LWR) and advanced reactor concepts. Unlike canonical channel flow,
the flow in rod bundles presents some unique characteristics, notably due to
the inhomogeneous cross section which can present different local conditions of
turbulence as well as localized effects characteristic of external flows.
Despite the ubiquity of rod bundle flows and the decades of experimental and
numerical knowledge acquired in this field, there are no publicly available
direct numerical simulations (DNS) of the flow in multiple pin rod bundles with
heat transfer. A multiple pin DNS study is of great value as it would allow for
assessment of the reliability of various turbulence models in the presence of
heat transfer, as well as allow for a deeper understanding of the flow physics.
We present work towards DNS of the flow in a square 5x5 rod bundle
representative of LWR fuel. We consider standard configurations as well as
configurations where the central pin is replaced with a guide thimble. We
perform simulations in STAR-CCM+ to design the numerical DNS, which is to be
conducted using the open source spectral element code Nek5000. Large Eddy
Simulations are also performed in Nek5000 to confirm that the resolution
requirements are adequate. We compare results from STAR-CCM+ and Nek5000, which
show very good agreement in the wide gaps with larger discrepancies in the
narrow gaps. In particular, evidence of a gap vortex street is seen in the edge
subchannels in LES but is not predicted by STAR-CCM+.

27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
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The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th