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Title: The golden-mean surface pattern to enhance flow oscillation in micro-channel
Authors: Wang, JF
Liu, Y 
Xu, YS
Keywords: Time-averaged drag
Downstream cylinder
Trouhal number
Issue Date: 2007
Source: 16th Australasian Fluid Mechanics Conference, Gold Coast, Queensland, Australia., December 3-7, 2007, p. 750-757 (CD-ROM) How to cite?
Abstract: This paper presents the effect of the diameter of a cylinder and Reynolds number (Re) on time-averaged drag (CD), rms drag (CDrms), rms lift (CLrms) and Strouhal number (St) in the wake of a downstream cylinder. The Re range considered is 7×103 ~ 3.3×104. The upstream cylinder diameter d investigated was 6, 10, 15, 20 and 25 mm, while the downstream cylinder diameter D was 25 mm, corresponding to d/D ranging from 0.24 ~ 1.0. The spacing ratio L/d (where L is the distance between the center of the upstream cylinder center and the leading stagnation point of the downstream cylinder) is 1, 2 and 5.5, covering different flow regimes. At L/d = 1, d/D = 1.0, increasing Re results a switching of a steady-reattachment to alternating-reattachment of the two free shear layers of the upstream cylinder on the downstream cylinder at Re = 23250, augmenting the width between the two free shear layers in the gap between the cylinders. As decreasing d/D corresponds to diminishing width between the free shear layers in the gap, the steady-reattachment of the shear layers occurred for d/D < 1.0 at L/d = 1 and for d/D < 0.8 at L/d = 2. While increasing d/D from 0.24 to 1.0 at L/d = 5.5 changes St from 0.203 to 0.12, that at L/d = 1 and 2 has little or no influence on St. An augmentation of d/D from 0 (isolated cylinder) progressively to 0.24, 0.4, 0.6 to 0.8 causes a reduction in CD by about 12~15%, 24~30%, 67~72% and 87~94% at L/d = 1 and 6~20%, 36~38%, 73~77% and 86~91% at L/d = 2, respectively. As d/D grows from 0.24 to 1.0, CD at L/d = 1 and 2 decays faster with d/D than at L/d = 5.5. d/D = 0.24~0.6 in the reattachment regime (i.e., at L/d =1 and 2) may generate streamwise vibration of the cylinder at fv/fn1 ≈ 0.5 and 1, in addition to at fv/fn1 = 2, where fv and fn1 are the vortex-shedding and first-modenatural frequencies of the cylinder. At L/d = 5.5, CDrms and CLrms grow with d/D. On the other hand, at L/d = 1 and 2, CDrms is more or less constant and CLrms diminishes with d/D.
ISBN: 978-1-864998-94-8
Appears in Collections:Conference Paper

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