Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Finite-size spherical particles in a square duct flow of an
  elastoviscoplastic fluid: an experimental study   The present experimental study addresses the flow of a Yield Stress Fluid
with some elasticity (Carbopol gel) in a square duct. The behaviour of two
fluids with lower and higher yield stress is investigated at multiple Reynolds
numbers $Re^* \in$ (1, 200) and Bingham numbers $Bi \in$ (0.01, 0.35). A
secondary flow consisting of eight vortices is observed to recirculate the
fluid from the corners to the core. Their extent and intensity grows with
increasing $Re^*$. The second objective of this study is to explore the change
in flow in the presence of particles. Almost neutrally-buoyant finite-size
spherical particles with duct height, $2H$, to particle diameter, $d_p$, ratio
of 12 are used at two volume fractions $\phi$ = 5 and 10\%. Particle Tracking
Velocimetry (PTV) is used to measure the velocity of these
refractive-index-matched spheres, and PIV to extract the fluid velocity. Simple
shadowgraphy is also used for qualitatively visualising the development of the
particle distribution along the streamwise direction. The particle distribution
pattern changes from being concentrated at the four corners, at low flow rates,
to being focussed along a diffused ring between the center and the corners, at
high flow rates. The presence of particles induces streamwise and wall-normal
velocity fluctuations in the fluid phase; however, the primary Reynolds shear
stress is still very small compared to turbulent flows. The size of the plug in
the particle-laden cases appears to be smaller than the corresponding single
phase cases. Similar to Newtonian fluids, the friction factor increases due to
the presence of particles, almost independently of the suspending fluid matrix.
Interestingly, predictions based on an increased effective suspension viscosity
agrees quite well with the experimental friction factor for the concentrations
used in this study.

35
The categories of this paper are: mtrl-th
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
6
The categories of this paper are: astro-ph
12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
18
The categories of this paper are: econ
9
The categories of this paper are: nlin
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga