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Drag Coefficient Enhancement of Dual Cylinders in Oscillatory Flow
Dixia Fan1*
, Xiaotong Zhang2, Michael S. Triantafyllou
1
1 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
2 State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering,
Shanghai Jiao Tong University, Shanghai, China
ABSTRACT
In this study, both experiments and numerical simulations have been
performed to study sinusoidal oscillations of an identical pair of
circular cylinders in a side-by-side configuration for various gaps in the
still fluid. The key parameter of Keulegan-Carpenter (KC) number in
the experiment is chosen between 0.5 and 20, Strokes number
(β=𝑅𝑒 𝐾𝐶⁄ ) values are selected from 350 to 2810 and gap ratio is
selected from 0.5 to 3 in the experiments. Compared to the single
cylinder cases, a large drag coefficient increase has been observed for
gap ratios from 0.5 to 1.0. This phenomenon has later been confirmed
by numerical simulations (in a smaller fixed Reynolds number of 120)
using Lily-Pad, a solver built on boundary data immersed method
(BDIM). In the numerical results, wake visualization shows that
vortices shed from the cylinder pair will induce a jet between the gap,
forming a vortex pair and accelerating the fluid particles away. This jet
motion helps to expel energy from the structure into the fluid, and is
confirmed by the energy flux calculation on the control volume around
the cylinder pair, thus explains the enhancement of the drag coefficient.