Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Drag and lift forces on a counter-rotating cylinder in rotating flow   Results are reported of an experimental investigation into the motion of a
heavy cylinder free to move inside a water-filled drum rotating around a
horizontal axis. The cylinder is observed to either co- or, counter
intuitively, counter-rotate with respect to the rotating drum. The flow was
measured with particle image velocimetry (PIV), and it was found that the inner
cylinder significantly altered the bulk flow field from the solid-body rotation
found for a fluid filled drum. In the counter-rotation case, the generated lift
force allowed the cylinder to freely rotate without contact with the drum wall.
Drag and lift coefficients of the freely counter-rotating cylinder were
measured over a wide range of Reynolds numbers, 2,500 $<$ Re $<$ 25,000,
dimensionless rotation rates, 0.0$ < \alpha < $1.2, and gap to cylinder
diameter ratios 0.003 $< G/2a <$ 0.5. Drag coefficients were consistent with
previous measurements on a cylinder in a uniform flow. However, for the lift
coefficient considerable larger values were observed in the present
measurements. We found the enhancement of the lift force to be mainly caused by
the vicinity of the wall.

26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
21
The categories of this paper are: adap-org
9
The categories of this paper are: nlin