Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The drag-adjoint field of a circular cylinder wake at Reynolds numbers
  20, 100 and 500   This paper analyzes the adjoint solution of the Navier-Stokes equation. We
focus on flow across a circular cylinder at three Reynolds numbers, Re_D=20,
100 and 500. The quantity of interest in the adjoint formulation is the drag on
the cylinder. We use classical fluid mechanics approaches to analyze the
adjoint solution, which is a vector field similar to a flow field. Production
and dissipation of kinetic energy of the adjoint field is discussed. We also
derive the evolution of circulation of the adjoint field along a closed
material contour. These analytical results are used to explain three numerical
solutions of the adjoint equations presented in this paper. The adjoint
solution at Re_D=20, a viscous steady state flow, exhibits a downstream suction
and an upstream jet, opposite of the expected behavior of a flow field. The
adjoint solution at Re_D=100, a periodic 2D unsteady flow, exhibits periodic,
bean shaped circulation in the near wake region. The adjoint solution at
Re_D=500, a turbulent 3D unsteady flow, has complex dynamics created by the
shear layer in the near wake. The magnitude of the adjoint solution increases
exponentially at the rate of the first Lyapunov exponent. These numerical
results correlate well with the theoretical analysis presented in this paper.

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The categories of this paper are: stat
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The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio
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The categories of this paper are: adap-org
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The categories of this paper are: hep-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: supr-con
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The categories of this paper are: eess
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The categories of this paper are: astro-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: hep-lat