On vortex formation from a cylinder. Part 1. The initial instability

Ünal, M. F.; Rockwell, D.

doi:10.1017/s0022112088001429

Cited by 252 publications

(112 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…A transition occurs in the shear layer region at Re ≈ 1000; it consists in the emergence of small-scale spanwise vortices comparable to those observed in plane mixing layers. These shear layer vortices and their formation frequency have been well documented [11][12][13][14][15][16][17][18][19][20][21]. The shear layer region also undergoes a three-dimensional transition, which includes a three-dimensional distortion of the shear layer vortices, as pointed out by Wei and Smith [13] and Rai [21], who visualized this phenomenon for Re ∈ [2400,4500] and Re = 3900, respectively.…”

Section: Introductionmentioning

confidence: 87%

“…Bloor [11] detected these vortices by measuring velocity fluctuations close to the detached shear layers and suggested a ratio between the shear layer frequency f SL and the shedding frequency of the primary wake vortices f St varying as Re 0.5 . The evolution of this frequency ratio as a function of Re has been discussed in a number of studies [12][13][14][15][16][17][18][19][20][21]. By fitting many measurements over a wide range of Reynolds numbers, Prasad and Williamson [16] proposed the following relation:…”

Section: Appendix C: Temporal Frequency Analysis Of the Shear Layersmentioning

confidence: 99%

See 1 more Smart Citation

Three-dimensional flow past a fixed or freely vibrating cylinder in the early turbulent regime

2018

View full text Add to dashboard Cite

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in: http://oatao. The three-dimensional structure of the flow downstream of a circular cylinder, either fixed or subjected to vortex-induced vibrations, is investigated by means of numerical simulation, at Reynolds number 3900, based on the cylinder diameter and current velocity. The flow exhibits pronounced fluctuations distributed along the span in all studied cases. Qualitatively, it is characterized by spanwise undulations of the shear layers separating from the body and the development of vortices elongated in the plane normal to its axis (planar vortices). A quantitative analysis of crossflow vorticity fluctuations in the spanwise direction reveals a peak of fluctuation amplitude in the near region (i.e., area of formation of the spanwise wake vortices) and opposite trends of the spanwise wavelength in the shear layer and wake regions; the wavelength tends to decrease as a function of the streamwise distance in the shear layers down to a minimum value close to 0.5 body diameters and then slowly increases further in the wake. The spanwise structure of the flow is differently altered in these two regions, once the cylinder vibrates. In the shear layer region, body motion is associated with an enhancement of planar vortex formation. The amplification of vorticity spanwise fluctuations in this region is accompanied by a reduction of the spanwise wavelength; it is found to decrease as a function of the instantaneous Reynolds number based on the instantaneous flow velocity seen by the moving body, following the global trend of the wavelength versus Reynolds number previously reported for fixed cylinders. In the wake region, the flow spanwise structure is essentially unaltered compared to the fixed body case, in spite of the major distortions of the streamwise and crossflow length scales.

show abstract

Section: Introductionmentioning

confidence: 87%

Section: Appendix C: Temporal Frequency Analysis Of the Shear Layersmentioning

confidence: 99%

Three-dimensional flow past a fixed or freely vibrating cylinder in the early turbulent regime

2018

View full text Add to dashboard Cite

show abstract

“…The inverse correlation observed between the base pressure and the vortex formation length in the flow past bluff bodies as a function of the Reynolds number is a well known phenomenon, which has been the object of different studies (e.g., see Ref. 36). However, their correlation in the unsteady flow has received lesser attention.…”

Section: A Energy Spectrummentioning

confidence: 99%

Low-frequency unsteadiness in the vortex formation region of a circular cylinder

Lehmkuhl

Rodríguez

Borrell³

et al. 2013

Physics of Fluids

128

View full text Add to dashboard Cite

The presence of low-frequency fluctuations in the wake of bluff bodies have been observed in several investigations. Even though the flow past a circular cylinder at Re = 3900 (Re = U ref D/ν) has been the object of several experimental and numerical investigations, there is a large scattering in the average statistics in the near wake. In the present work, the flow dynamics of the near wake region behind a circular cylinder has been investigated by means of direct numerical simulations and statistics have been computed for more than 858 shedding cycles. The analysis of instantaneous velocity signals of several probes located in the vortex formation region, point out the existence of a low-frequency fluctuation at the non-dimensional frequency of f m = 0.0064. This large-scale almost periodic motion seems to be related with the modulation of the recirculation bubble which causes its shrinking and enlargement over the time.

show abstract

“…The insignificant Re effect is connected to the fact that the vortex formation length in an isolated cylinder wake is insensitive to Re for Re= ͑2.0ϫ 10 4 ͒ -͑2.0ϫ 10 5 ͒. 12,28,43 Type 4C corresponds to the regions of ␣ = 88°-90°and P ‫ء‬ = 1.7-2.7, where the gap flow is biased at low Re, producing a narrow street of higher St and a wide street of lower St. With increasing Re, the two distinct St values approach each other and eventually meet at StϷ 0.2 ͓Fig. 13͑f͔͒, which implies that the gap flow is not biased any more and two antiphased streets of the same St occur, each similar to that behind an isolated cylinder.…”

Section: -9mentioning

confidence: 99%

Reynolds number effect on the wake of two staggered cylinders

et al. 2009

View full text Add to dashboard Cite

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.

show abstract

On vortex formation from a cylinder. Part 1. The initial instability

Cited by 252 publications

References 22 publications

Three-dimensional flow past a fixed or freely vibrating cylinder in the early turbulent regime

Three-dimensional flow past a fixed or freely vibrating cylinder in the early turbulent regime

Low-frequency unsteadiness in the vortex formation region of a circular cylinder

Reynolds number effect on the wake of two staggered cylinders

Contact Info

Product

Resources

About