An Experimental Study on Aerodynamic Drag of Rectangular Cylinders

Nakaguchi, Hiroshi; Hashimoto, Kikuhiro; Muto, Shinri

doi:10.2322/jjsass1953.16.1

Cited by 127 publications

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“…The St dependence on P ‫ء‬ resembles that on the width-to-height ratio ͑an indication of after-body length͒ in a rectangular cylinder wake, where St diminishes gradually as the width-to-height ratio increases up to 2.8. [31][32][33] For ReϾ Re c , the shear layer reattachment results in a narrowed wake behind the downstream cylinder and hence a higher St, which is highly dependent on the reattachment location on the downstream cylinder. 34 A shear layer reattaching on the downstream side of the cylinder is led toward the centerline ͓Fig.…”

Section: -5mentioning

confidence: 99%

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: -5mentioning

confidence: 99%

Reynolds number effect on the wake of two staggered cylinders

et al. 2009

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“…C pb is almost independent of Re (see results in our previous study (16) and the results for a two-dimensional prism (or a pipe with d/t = ∞) (25) - (27) and a rod/disc (or a pipe with d/t = 1.0) (24) by other researchers. We can see that C pb monotonically decreases with increasing l/t, if d/t is fixed to a certain value of 4.0 or 8.0.…”

Section: Base-suction Coefficientmentioning

confidence: 79%

High-Reynolds-Number Flow past a Pipe

Hirata

Sakata

Yajima

et al. 2013

JFST

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The present aim is to reveal the flow past a pipe which is immersed parallel to the mainstream at high Reynolds numbers. In a wind tunnel, we carry out (1) base-pressure measurements, (2) velocity-fluctuation measurements using a hot-wire anemometer and (3) flow visualisations by a smoke-wire method with PIV analyses, where we take consecutive picutures using a high-speed camcorder to obtain quantitative flow-field information such as velocity vector and vorticity. The tested parameter ranges are as follows: Re = 2.0×10 3 -1.3×10 4, d/t = 4.0 -10.0 and l/t = 1.0 -10.0, where Re, d, t and l are the Reynolds number, mean diameter, thickness and length of the pipe, respectively. As a result, the Re effects are negligible. The base-suction coefficient C pb monotonically decreases with decreasing d/t, or with increasing l/t. We propose a unified formula to predict C pb , which are consistent with both a two-dimensional prism and a rod for l/t < 4.0 in addition to a ring. In contrast, the Strouhal number St almost coincides with that for a two-dimensional prism at any l/t, if we can detected any dominant frequencies. In addition, we conduct flow visualisations, and reveal the effects upon axisymmetry of wake. Finally, we classify the flow into three modes based on both periodicity and axisymmetry. Such a modal classification reveals that the enhancement of flow's irregularity corresponds to the decrease of C pb .Key Words: IntroductionWhile the flow past a bluff body at higher Reynolds numbers often becomes important in many practical aspects, it is one of rather later topics in the long history of fluid mechanics. Among such bluff-body-flow problems, there have been less researches concerning three-dimensional bluff bodies, in comparison with well-researched two-dimensional ones such as a circular cylinder which has advantages in some compatibilities with analytical, experimental and numerical approaches.As basic three-dimensional bluff bodies, it seems natural to consider axisymmetrical bodies with simple geometries like a sphere and a disc, whose knowledge is useful in the analyses of flying or suspended objects. But, even the flow past such a simple axisymmetrical body has not been revealed enough, despite of the wide ranges of its engineering applicabilities, in comparison with a circular cylinder.The present study concerns the flow past another simple axisymmetrical bluff body, a pipe or a tube, which is immersed parallel to the mainstream at high Reynolds numbers. The researches on the flow have been still less active than a sphere or a disc, although the knowledge is useful in many industrial fields, such as the designs for combustors, ventilator (2) − (8)

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“…The differences between numerical simulation results and physical experiment data [4,5] can be registried with the help of a drag coefficient that is shown on figure 2. Figure 3 shows isolines of pressure distribution for square cylinder.…”

Section: Numerical Algorithmmentioning

confidence: 99%

Quasihydrodynamic model and small-scale turbulence

Ivakhnenko

Polyakov

Четверушкин

2009

Math Models Comput Simul

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Key words: system of quasi-hydrodynamics equations, scale of turbulence, dissipative terms.Abstract. The averaged quasi-hydrodynamic (QHD) system of equations describing small-scale turbulence and its implementation is presented. The QHD equations differ from the Navier-Stokes ones by additional dissipative terms. For low and middle speed flows these terms are related to the molecular viscosity coefficient. The obtained results were compared with results of other authors and physical experiments. For comparison of numerical and experimental results the averaged drag coefficient is used. The results precision of simulation depends on mesh size therefore demands significant computing resources. The general aspect of this paper is increasing quality of numerical solution on rough meshes. This model was tested on a set of simple shapes.

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An Experimental Study on Aerodynamic Drag of Rectangular Cylinders

Abstract: An experimental study is carried out on the

Cited by 127 publications

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Reynolds number effect on the wake of two staggered cylinders

Reynolds number effect on the wake of two staggered cylinders

High-Reynolds-Number Flow past a Pipe

Quasihydrodynamic model and small-scale turbulence

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