Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: How does filtering change the perspective on the scale-energetics of the
  near-wall cycle?   We investigate the flux of kinetic energy across length scales in a turbulent
pipe flow. We apply explicit spatial filtering of DNS data and assess the
effect of different filter kernels (Fourier, Gauss, box) on the local structure
of the inter-scale energy flux ($\Pi$) and its statistics. Qualitatively, the
mean energy flux at each wall-normal distance is robust with respect to the
filter kernel, whereas there are significant differences in the estimated
intensity and distribution of localised $\Pi$ events. We find conflicting
correlations between typical flow structures in the buffer layer (streaks,
vortices and different $Q$ events) and regions of forward/backward transfer in
the instantaneous $\Pi$ field. In particular, cross-correlations are highly
upstream-downstream symmetric for the Fourier kernel, but asymmetric for the
Gauss and box kernel. We show that for the Gauss and box kernel, $\Pi$ events
preferably sit on the inclined meander at the borders of streaks where strong
shear layers occur, whereas they appear centred on top of the streaks for the
Fourier kernel. Moreover, using the Fourier kernel we reveal a direct
coincidence of backward scatter and fluid transport away from the wall
($Q_{1}$), which is absent for the Gauss and the box kernel. However, all
kernels equally predict backward scatter directly downstream of $Q_{1}$ events.
Our findings expand the common understanding of the wall cycle and might impact
modelling and control strategies. Altogether, our results suggest that
interpretations of the inter-scale energy flux relying on Fourier filters
should be taken with caution, because Fourier filters act globally in physical
space, whereas $\Pi$ events are strongly spatially localised. Our Python
post-processing tool eFlux for scale separation and flux computations in pipe
flows is freely available and can be easily adapted to other flow geometries.

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The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
30
The categories of this paper are: q-alg
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The categories of this paper are: q-bio
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The categories of this paper are: econ
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The categories of this paper are: astro-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: ao-sci
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The categories of this paper are: supr-con
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The categories of this paper are: math-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ex