Characteristics of the Flow around Two Circular Cylinders Arranged in Tandem : 1st Report

Igarashi, Tamotsu

doi:10.1299/jsme1958.24.323

Cited by 387 publications

(197 citation statements)

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“…The latter results from a transition of the shear layer, separating from the upstream cylinder, from the reattachment to the coshedding regime. 5,10,12,18 The present critical P ‫ء‬ , between 4.0 and 4.5, is slightly smaller than the measurements of Xu and Zhou. 13 The deviation is not unexpected.…”

Section: Configurations Of ␣ = 0°and 90°: Validation Of Measuremcontrasting

confidence: 76%

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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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Section: Configurations Of ␣ = 0°and 90°: Validation Of Measuremcontrasting

confidence: 76%

“…9͑a͔͒ and the two cylinders act like a single body, with stagnant fluid in their gap. 5,10 This explains why St is close to St 0 . For Re Ͻ Re c , St at a given P ‫ء‬ drops slowly and monotonically with …”

Section: B Typementioning

confidence: 88%

Reynolds number effect on the wake of two staggered cylinders

et al. 2009

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“…It is well known that the flow may be classified into three regimes at α = 0 • , i.e. the single-body regime, the reattachment regime and the co-shedding regime (Igarashi 1981;Zdravkovich 1987). For all three regimes, the flow behind the cylinders is characterized by a single vortex street (e.g.…”

Section: Mode S-iimentioning

confidence: 99%

“…Williamson 1985; Kolář, Lyn & Rodi 1997;Sumner et al 1999;Zhou et al 2001Zhou et al , 2002Zhou & Yiu 2006), Strouhal number St (e.g. Igarashi 1981Igarashi , 1984Kim & Durbin 1988;Xu & Zhou 2004) and forces on the cylinders (e.g. Zdravkovich 1977Zdravkovich , 1985Zdravkovich , 1987Mahir & Rockwell 1996).…”

Section: Introductionmentioning

confidence: 99%

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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“…9 The downstream cylinder was demonstrated to be the dominant noise source, which is characterised with tonal noise at the shedding frequency. For a typical landing gear, the separation distance of the tandem wheels is between 1.1D and 1.5D, 10 and in such a range, the shear layer from the upstream cylinder is expected to reattach on the downstream cylinder, 11,12,13,14 and no regular shedding can be observed. Additionally, wheels can be considered as circular cylinders of short aspect ratios, the flow field surrounding which is more complex compared to the large aspect ratio circular cylinders.…”

Section: Introductionmentioning

confidence: 99%

Interaction Noise from Tandem Landing Gear Wheels with Hub and Rim Cavities

Wang

Angland

Scotto

2017

23rd AIAA/CEAS Aeroacoustics Conference

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Wheels are major noise sources on landing gears. Accurate numerical predictions of wheel noise can provide insights into landing gear noise generation mechanisms and help improve landing gear noise prediction models. Previous simulations have been conducted on an isolated high-fidelity wheel model containing a tyre, a hub, a sidewall and two rim cavities. The hub cavity was an important middle frequency noise source due to the first and second hub cavity depth modes, and the rim cavities were major high frequency noise sources. This work investigates the major noise sources in different frequency ranges of two tandem wheels, with the same geometry as the previous isolated wheel case, by performing high-order numerical simulations at M = 0.23. This paper focuses on the mechanisms and characteristics of the wheel interaction noise. The aerodynamic results are validated against experiments and demonstrate reasonable agreements. The flow interactions are found to be mainly in the side direction with a spectral peak in the side force at a Strouhal number of 0.19, based on the wheel width, which is due to a flapping shear layer mode in the gap. The downstream wheel is the major noise source and has a favourable sound radiation direction to the sideline. The effects of the downstream wheel hub and rim cavities are isolated by covering them in the simulations. The flow interactions dominate the hub cavity depth modes in the generation of middle frequency downstream wheel noise. For high frequency noise, covering both the hub and rim cavities on the downstream wheel only, reduced the noise radiated towards the ground. This high frequency noise reduction was not achieved when the hub cavity alone was covered.

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Characteristics of the Flow around Two Circular Cylinders Arranged in Tandem : 1st Report

Cited by 387 publications

References 0 publications

Reynolds number effect on the wake of two staggered cylinders

Reynolds number effect on the wake of two staggered cylinders

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

Interaction Noise from Tandem Landing Gear Wheels with Hub and Rim Cavities

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