Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct Numerical Simulations of the Swirling von Karman Flow Using a
  Semi-implicit Moving Immersed Boundary Method   We present a novel moving immersed boundary method (IBM) and employ it in
direct numerical simulations (DNS) of the closed-vessel swirling von Karman
flow in laminar and turbulent regimes. The IBM extends direct-forcing
approaches by leveraging a time integration scheme, that embeds the immersed
boundary forcing step within a semi-implicit iterative Crank-Nicolson scheme.
The overall method is robust, stable, and yields excellent results in canonical
cases with static and moving boundaries. The moving IBM allows us to reproduce
the geometry and parameters of the swirling von Karman flow experiments in (F.
Ravelet, A. Chiffaudel, and F. Daviaud, JFM 601, 339 (2008)) on a Cartesian
grid. In these DNS, the flow is driven by two-counter rotating impellers fitted
with curved inertial stirrers. We analyze the transition from laminar to
turbulent flow by increasing the rotation rate of the counter-rotating
impellers to attain the four Reynolds numbers 90, 360, 2000, and 4000. In the
laminar regime at Reynolds number 90 and 360, we observe flow features similar
to those reported in the experiments and in particular, the appearance of a
symmetry-breaking instability at Reynolds number 360. We observe transitional
turbulence at Reynolds number 2000. Fully developed turbulence is achieved at
Reynolds number 4000. Non-dimensional torque computed from simulations matches
correlations from experimental data. The low Reynolds number symmetries, lost
with increasing Reynolds number, are recovered in the mean flow in the fully
developed turbulent regime, where we observe two tori symmetrical about the
mid-height plane. We note that turbulent fluctuations in the central region of
the device remain anisotropic even at the highest Reynolds number 4000,
suggesting that isotropization requires significantly higher Reynolds numbers.

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The categories of this paper are: math-ph
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The categories of this paper are: nlin
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The categories of this paper are: gr-qc
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The categories of this paper are: adap-org
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The categories of this paper are: math
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The categories of this paper are: eess
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The categories of this paper are: econ
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The categories of this paper are: q-fin
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The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-th
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The categories of this paper are: cond-mat
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The categories of this paper are: q-bio