Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 3D flow motions in the viscous sublayer   We employ novel digital Fresnel reflection holography to capture the 3D flows
within the viscous sublayer of a smooth-wall turbulent channel flow at
Re{\tau}=400. The measurements reveal unsteady and diverse flow patterns in the
sublayer including nearly uniform high and low speed flows and strong
small-scale (on the order of viscous wall units) spanwise meandering motions.
The probability density functions (PDFs) of wall shear stresses show a clear
discrepancy in high stress range with those from direct numerical simulation
(DNS), which is attributed to the unresolved streamwise and spanwise motions by
DNS. Moreover, the PDF of Lagrangian particle accelerations yields a stretched
exponential shape like that in homogenous isotropic turbulence, indicating
strong intermittency in the sublayer. We find a significant fraction of high
accelerations is associated with the small-scale meandering motions. Our study
helps explain the effect of sublayer-scale roughness on reducing drag and flow
separation reported in the literature.

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The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg
2
The categories of this paper are: math