Objectives: The present study examines the effect of unequal gap
spacing for flow past over three rectangular rods a fixed Re (Reynolds number)
and an Aspect Ratio (AR).
Background: In computational fluid dynamics, the numerical study
of flow past over a single or more than one object has a great impact on the
scientific community for suitable selection of parameters such as Reynolds
number, gap spacing, and Aspect ratio. Their suitable choice is used to control
flow for the purpose of saving energy in order to avoid damaging of structure
by reducing the fluid forces and to suppress the vortex shedding.
Methodology: A two-dimensional (2-D) numerical study of flow over
three rectangular Rods is conducted by using the Single Relaxation Time Lattice
Boltzmann Method (SRTLBM). The gap spacing ( g ) between the rods is varied
from 0.5 to 7 with a fixed Reynolds number i.e., Re = 150(Re = U ∞ d/v), (where
U∞ is uniform velocity, d is the size of an object and v is the kinematic
viscosity) and aspect ratio AR = 0.25 (where, AR = 1/w,1 is the length and w is
the width of the rods). Different flow structures, power spectra analysis of
lift coefficients and force statistics are studied for this analysis at small,
moderate and large gap spacing.
Results: The present study revealed that the gap spacing between
the rods has a great impact on the flow behavior. Therefore, different flow
patterns are observed and some of them are outlined as, i). Shear layer
reattachment (SLR), ii). Semi developed single bluff body (SDSBB), iii). Fully
developed vortex shedding (FDVS), iv). Semi developed irregular vortex
shedding, v) Fully generated two-row single bluff body, vi). Semi developed
irregular single bluff body (SDISBB) and vii). Critical flow (CF) patterns. The
critical flow behavior is observed at the gap spacing (g1,g2) = (5,2.5) ,
(here, g1 is the gap between upstream rods to middle one and g2 is the gap
between middle rods to downstream rectangular rod). The power spectrum analysis
of large wake regimes of different flow patterns showed distortion. Irregularities,
multiple peaks and in some cases secondary peaks are also observed. Multi-peaks
represent irregular behavior. While secondary peaks and distortion enable us to
conclude that a critical flow pattern has been observed at certain points. In
force statistics analysis, the values of Cdmean and Strouhal number are
computed at different spacing ratios. The value of mean drag coefficients for
all three rods at g1=3 is approximately the same, but at g1=1 and 5, the
maximum value of Cdmean is observed for C2 as compared to C1 and C3, which is
6.91. Furthermore, Strouhal number values are much less than the single rod
(SR) value for all three chosen small, moderate and large gap spacing values.
The maximum value of St is examined at (g1,g2) = (1,1) i.e. 0.19. The amplitude
of the values of the Strouhal number varied with the increase in the gap
spacing. At critical flow, the Strouhal number has primary and secondary peaks,
which depict the unsteadiness in the flow.
Author(s)
Details
Shams-Ul
Islam
Department of Mathematics, Comsats University Islamabad,
Islamabad, 44000, Pakistan.
R.
Manzoor
Department of Mathematics, SBK Women's University, Quetta,
Pakistan.
M.
Zahid
School of Mathematics and Statistics, Zhengzhou University, China.
S.
Kulsoom
Department of Mathematics, SBK Women's University, Quetta,
Pakistan.
U.
Kausar
Department of Mathematics, SBK Women's University, Quetta,
Pakistan.
Please see the book here:- https://doi.org/10.9734/bpi/mcscd/v2/852
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