On interference between two circular cylinders in staggered arrangement at high subcritical Reynolds numbers

Gu, Zhiyuan; Sun, Tianfeng

doi:10.1016/s0167-6105(98)00205-0

Cited by 108 publications

(110 citation statements)

References 10 publications

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“…At a higher Re, the inner shear layer separating from the upstream cylinder bifurcates (figures 15a and 15f ). The same observation was made by Gu & Sun (1999) at Re = 5600 and Alam & Sakamoto (2005) at Re = 55 000. While the outer shear layer, separating from the upstream cylinder, rolls up to form one row of vortices, the inner bifurcates once reattaching on the downstream cylinder, partly forming the gap flow between the cylinders and partly joining the shear layer separating from the downstream cylinder to form another row of vortices.…”

Section: Mode S-iasupporting

confidence: 78%

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Flow structure behind two staggered circular cylinders. Part 1. Downstream evolution and classification

Zhou

2008

J. Fluid Mech.

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Flow structures, Strouhal numbers and their downstream evolutions in the wake of two-staggered circular cylinders are investigated at Re = 7000 using hot-wire, flowvisualization and particle-image velocimetry techniques. The cylinder centre-to-centre pitch, P , ranges from 1.2d to 4.0d (d is the cylinder diameter) and the angle (α) between the incident flow and the line through the cylinder centres is 0 • ∼ 90 • . Four distinct flow structures are identified at x/d > 10 (x is the downstream distance from the mid-point between the cylinders), i.e. two single-street modes (S-I and S-II) and two twin-street modes (T-I and T-II), based on Strouhal numbers, flow topology and their downstream evolution. Mode S-I is further divided into two different types, i.e. SIa and S-Ib, in view of their distinct vortex strengths. Mode S-Ia occurs at P /d 6 1.2. The pair of cylinders behaves like one single body, and shear layers separated from the free-stream sides of the cylinders roll up, forming one street of alternately arranged vortices. The street is comparable to that behind an isolated cylinder in terms of the topology and strength of vortices. Mode S-Ib occurs at α 6 10 • and P /d > 1.5. Shear layers separated from the upstream cylinder reattach on or roll up to form vortices before reaching the downstream cylinder, resulting in postponed flow separation from the downstream cylinder. A single vortex street thus formed is characterized by significantly weakened vortices, compared with Mode S-Ia. Mode S-II is identified at P /d = 1.2 ∼ 2.5 and α > 20 • or 1.5 6 P /d 6 4.0 and 10 • < α 6 20 • , where both cylinders generate vortices, with vortex shedding from the upstream cylinder at a much higher frequency than from the downstream, producing two streets of different widths and vortex strengths at x/d 6 5.0. The two streets interact vigorously, resulting in a single street of the lower-frequency vortices at x/d > 10. The vortices generated by the downstream cylinder are significantly stronger than those, originating from the upstream cylinder, in the other row. Mode T-I occurs at P /d > 2.5 and α = 20 • ∼ 88 • ; the two cylinders produce two streets of different vortex strengths and frequencies, both persisting beyond x/d = 10. At P /d > 2.5 and α > 88 • , the two cylinders generate two coupled streets, mostly anti-phased, of the same vortex strength and frequency (St ≈ 0.21), which is referred to as Mode T-II. The connection of the four modes with their distinct initial conditions, i.e. interactions between shear layers around the two cylinders, is discussed. † Author to whom correspondence should be addressed: mmyzhou@polyu.edu.hk 52 J. C. Hu and Y. Zhou IntroductionBecause of its fundamental importance and engineering significance, flow behind two circular cylinders has been investigated extensively. Most previous investigations focused on the wake of two side-by-side or inline cylinders because of their relative simplicity. As a result, our knowledge has been greatly improved on the two types of flow in terms of the dep...

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Section: Mode S-iasupporting

confidence: 78%

“…P * > 2.83 and α > 13 • , arising from the displacement of the upstream-cylinder wake by the flow around the downstream cylinder. Gu & Sun (1999) also observed an appreciable C L at P * = 1.7 and α = 15 • ∼ 16 • (Re = 2.2 × 10 5 ).…”

Section: Mode S-iimentioning

confidence: 70%

Flow structure behind two staggered circular cylinders. Part 1. Downstream evolution and classification

Zhou

2008

J. Fluid Mech.

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“…The isocontours of St were given and five regions were identified based on the measured St with reference to that, St 0 , in an isolated cylinder wake. Their ⌬␣ seems too large since the flow is highly sensitive to ␣ and P ‫ء‬ for ␣ Ͻ 20°and P ‫ء‬ Ͻ 2, 2,3,5,6 which implies the possible loss of important details on St. In their investigation of two staggered cylinders at Re= ͑3.2-7.4͒ ϫ 10 4 , Sumner and Richards 7 observed two distinct St values in both upstreamand downstream-cylinder-generated wakes for some P ‫ء‬ and ␣ ranges ͑e.g., P ‫ء‬ =1, ␣ =16°-75°͒, although the flow physics behind was not discussed.…”

Section: Introductionmentioning

confidence: 98%

Reynolds number effect on the wake of two staggered cylinders

et al. 2009

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This work aims to investigate, based on the measured/reported Strouhal number ͑St͒ and the flow structure, the Reynolds number ͑Re͒ effect on the wake of two identical cylinders with a diameter of d over P ‫ء‬ = P / d = 1.2-4.0 and ␣ = 0°-90°, where P is the center-to-center spacing between the two cylinders and ␣ is the angle of incident flow with respect to the line through the two cylinder centers. The Re range examined is from 1.5ϫ 10 3 to 2.0ϫ 10 4 . Two hotwires were used to measure St simultaneously behind each of the two cylinders. The St-Re relationship is classified into four distinct types, i.e., types 1-4. Each is linked to distinct initial conditions, viz., interactions between the four shear layers around the cylinders. Type 1 occurs at small P ‫ء‬ , not exceeding 1.25. The two cylinders act like a single body, producing a single St across the wake throughout the range of Re examined. On the other hand, type 2 occurs at small ␣ ͑Ͻ10°͒. Although single valued, the St in type 2 displays a sudden jump with increasing Re due to a switch in the shear layer, separated from the upstream cylinder, from overshooting to reattachment on the downstream cylinder ͑type 2A͒ or from reattachment to coshedding vortices ͑type 2B͒, depending on P ‫ء‬ . Type 3 is in the region of intermediate P ‫ء‬ ͓͑1.2-1.5͒-2.2͔ and ␣ ͑10°-75°͒. Two distinct St occur at low Re. The lower and the higher ranges of St are associated with the downstream and upstream cylinders, respectively. With increasing Re, the higher St collapses to the lower, which is attributed to a change in the inner shear layer, separated from the upstream cylinder, from squeezing through the gap between cylinders to reattachment on the downstream cylinder. Type 4 occurs at large P ‫ء‬ ͑Ͼ1.2-2.2͒ and again exhibits at low Re two St, above and below the Strouhal number St 0 in the wake of an isolated cylinder, both changing suddenly or progressively to St 0 with increasing Re, which results from a change in the inner shear layer, separated from the upstream cylinder, from reattachment on the downstream cylinder to forming vortices between the cylinders. These types of Re-St relationships are also connected to the flow structure modes reported in literature. The dependence of the St and St-Re relationships on P ‫ء‬ and ␣ is provided, which may be used for the prediction of St in related problems.

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“…Of particular challenge and interest to researchers is that the flow and resulting fluid dynamics over a cluster of closely spaced bluff bodies exhibit many intriguing features not found in the corresponding flow over an isolated single body. Complex interactions between shear-layers shed from the cylinders and vortex structures in the wake, as well as paradoxical flow-induced forces on the structure, have been reported even for the simplest of such configurations, namely, a pair of circular cylinders in cross-flow; see, for example, Nishimura (1986), Zdravkovich (1987), Gu & Sun (1999) Zdravkovich (1987) initially classified the flow over a pair of circular cylinders into three regimes, which he referred to as "no interface", "wake interface", and "proximity interface", with subdivisions for the last two categories. Gu & Sun (1999) extended this classification by subdividing the "wake interface" regime into two categories; namely "shear-layer interface" and "neighborhood interface".…”

Section: Introductionmentioning

confidence: 99%

“…Complex interactions between shear-layers shed from the cylinders and vortex structures in the wake, as well as paradoxical flow-induced forces on the structure, have been reported even for the simplest of such configurations, namely, a pair of circular cylinders in cross-flow; see, for example, Nishimura (1986), Zdravkovich (1987), Gu & Sun (1999) Zdravkovich (1987) initially classified the flow over a pair of circular cylinders into three regimes, which he referred to as "no interface", "wake interface", and "proximity interface", with subdivisions for the last two categories. Gu & Sun (1999) extended this classification by subdividing the "wake interface" regime into two categories; namely "shear-layer interface" and "neighborhood interface". Sumner, Price & Païdoussis (2000) suggested a much more detailed categorization of the flow, with three broad regimes: i) single bluff-body flows, ii) flows at low incidence, and iii) flows at high angles of incidence.…”

Section: Introductionmentioning

confidence: 99%

Wake Synchronization for a Pair of Staggered Cylinders in Cross-Flow with the Upstream Cylinder in Transverse Oscillation

Akbari

Price

2010

Engineering Applications of Computational Fluid Mechanics

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Numerical simulations are presented for the cross-flow over two staggered circular cylinders in the low subcritical Reynolds number regime with Re =1500, with the upstream of the two cylinders subject to a transverse harmonic oscillation. A vortex method is implemented for the solution of the unsteady two-dimensional Navier-Stokes equations. The effect of varying the frequency of oscillation of the upstream cylinder, with fixed amplitude of oscillation, is investigated. The numerical flow visualization results reveal a synchronization of the wake structure with the oscillating cylinder for different ranges of the excitation frequency. Four distinct synchronization modes are identified, and are compared with available experimental data.

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On interference between two circular cylinders in staggered arrangement at high subcritical Reynolds numbers

Cited by 108 publications

References 10 publications

Flow structure behind two staggered circular cylinders. Part 1. Downstream evolution and classification

Flow structure behind two staggered circular cylinders. Part 1. Downstream evolution and classification

Reynolds number effect on the wake of two staggered cylinders

Wake Synchronization for a Pair of Staggered Cylinders in Cross-Flow with the Upstream Cylinder in Transverse Oscillation

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