On the phenomenon of vortex street breakdown

Durgin, William W.; Karlsson, Sture K. F.

doi:10.1017/s0022112071001721

Cited by 40 publications

(44 citation statements)

References 9 publications

(13 reference statements)

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“…The latter has been demonstrated experimentally for evolving streets by Taneda [14], and Durgin and Karlsson [15] for single cylinders, while Thomas and Kraus [16] and Zdravkovich [17] made similar findings for multiple cylinder arrangements. Numerical studies by Acton [18] and Christiansen and Zabusky [19] have also exhibited coalesence.…”

Section: Lower Mode Response Of Circular Cylinders In Cross-flowmentioning

confidence: 60%

Lower Mode Response of Circular Cylinders in Cross-Flow

Durgin

March

Lefebvre

1980

Journal of Fluids Engineering

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Transverse amplitude responses of a circular cylinder in cross-flow were determined as a function of reduced velocities for a variety of spring constants and damping coefficients. Maxima were found at reduced velocities of 5 and 16, and were of comparable amplitude. The first resonance, designated the “fundamental mode,” was due to normal vortex street excitation of the spring-mass system. The second resonance, designated the “lower mode,” occurred when the natural frequency was approximately one-third of the normal vortex shedding frequency. By assuming that the driving force was sinusoidal, it was possible to evaluate the lift coefficients at resonance. Lift coefficients for the lower mode behaved similarly with amplitude ratio but were an order of magnitude lower than lift coefficients for the fundamental mode. A mechanism was used to oscillate the cylinder transversely at prescribed frequencies and amplitudes. Dominant wake frequencies were determined from a frequency analysis of the hot-wire signal for a range of velocities and a fixed frequency of oscillation. It was found that synchronization of the shedding frequency to the forcing frequency did not take place for the lower mode. The familiar “lock-in” region, or frequency synchronization over finite bandwidth, was observed for the fundamental mode only. Since the frequency associated with normal vortex shedding was not suppressed when oscillations took place in the lower mode, it would seem that a low frequency vortex street had not replaced the normal one. It is likely, then, that the spring-mounted cylinder responded subharmonically to the exciting force resulting from vortex shedding. In this regard, however, it was curious that subharmonic response was not found at a frequency ratio of 0.5 as it was at 0.33. A conceptual model, which incorporated features of both the low frequency vortex street and subharmonic response, was developed which accounted for lower mode response at a frequency ratio of 0.33 as well as the lack of response at 0.5.

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Section: Lower Mode Response Of Circular Cylinders In Cross-flowmentioning

confidence: 60%

Lower Mode Response of Circular Cylinders in Cross-Flow

Durgin

March

Lefebvre

1980

Journal of Fluids Engineering

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“…It is important to note that real wake vortices experience different effects to an isolated Lamb-Oseen vortex due to the fact that wake vortices are being advected downstream and there is interaction between neighbouring vortices, which leads to mutual straining and merging among the vortices. 32,33 Furthermore, wake vortices experience a confinement effect due to the duct wall, where in high-blockage cases, the vortices shed from the wall can cause dramatic changes in the global flow behaviour and modification of the flow structure. 34 On the other hand, an isolated vortex possesses a general structure of monotonic decrease of vorticity with radial distance from a central extremum.…”

Section: -3mentioning

confidence: 99%

“…32 This unstable secondary street possesses a longer wavelength than the primary street and contains more than one dominant frequency. 15 These two regions (the formation and unstable regions) exhibit complex vortex geometries and behaviour and hence, are not considered in the development of Eq.…”

Section: B Validation Of the Modelmentioning

confidence: 99%

Spatial evolution of a quasi-two-dimensional Kármán vortex street subjected to a strong uniform magnetic field

2015

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Spatial evolution of a quasi-two-dimensional Kármán vortex street subjected to a strong uniform magnetic field A vortex decay model for predicting spatial evolution of peak vorticity in a wake behind a cylinder is presented. For wake vortices in the stable region behind the formation region, results have shown that the presented model has a good capability of predicting spatial evolution of peak vorticity within an advecting vortex across 0.1 ≤ β ≤ 0.4, 500 ≤ H ≤ 5000, and 1500 ≤ Re L ≤ 8250. The model is also generalized to predict the decay behaviour of wake vortices in a class of quasi-two-dimensional magnetohydrodynamic duct flows. Comparison with published data demonstrates remarkable consistency. C 2015 AIP Publishing LLC.

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“…Apart from viscous diffusion, the geometric arrangement of the vortices in the vortex street determines whether it is predominately stable or whether it breaks down into parallel shear flow. A critical value was derived by Durgin & Karlsson (1971) as h/a = 0.365, where h is the cross-wake spacing between positive and negative wake vortices and a is the separation between vortices of the same sign. Above this critical value, the vortices stretch out and align with the downstream direction leading to a parallel shear flow.…”

Section: Introductionmentioning

confidence: 99%

Low-Reynolds-number wakes of elliptical cylinders: from the circular cylinder to the normal flat plate

et al. 2014

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While the wake of a circular cylinder and, to a lesser extent, the normal flat plate have been studied in considerable detail, the wakes of elliptic cylinders have not received similar attention. However, the wakes from the first two bodies have considerably different characteristics, in terms of three-dimensional transition modes, and near-and far-wake structure. This paper focuses on elliptic cylinders, which span these two disparate cases. The Strouhal number and drag coefficient variations with Reynolds number are documented for the two-dimensional shedding regime. There are considerable differences from the standard circular cylinder curve. The different three-dimensional transition modes are also examined using Floquet stability analysis based on computed two-dimensional periodic base flows. As the cylinder aspect ratio (major to minor axis) is decreased, mode A is no longer unstable for aspect ratios below 0.25, as the wake deviates further from the standard Bénard-von Kármán state. For still smaller aspect ratios, another three-dimensional quasi-periodic mode becomes unstable, leading to a different transition scenario. Interestingly, for the 0.25 aspect ratio case, mode A restabilises above a Reynolds number of approximately 125, allowing the wake to return to a two-dimensional state, at least in the near wake. For the flat plate, three-dimensional simulations show that the shift in the Strouhal number from the two-dimensional value is gradual with Reynolds number, unlike the situation for the circular cylinder wake once mode A shedding develops. Dynamic mode decomposition is used to characterise the spatially evolving character of the wake as it undergoes transition from the primary Bénard-von Kármán-like near wake into a two-layered wake, through to a secondary Bénard-von Kármán-like wake further downstream, which in turn develops an even longer wavelength unsteadiness. It is also used to examine the differences in the two-and three-dimensional near-wake state, showing the increasing distortion of the two-dimensional rollers as the Reynolds number is increased.

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On the phenomenon of vortex street breakdown

Cited by 40 publications

References 9 publications

Lower Mode Response of Circular Cylinders in Cross-Flow

Lower Mode Response of Circular Cylinders in Cross-Flow

Spatial evolution of a quasi-two-dimensional Kármán vortex street subjected to a strong uniform magnetic field

Low-Reynolds-number wakes of elliptical cylinders: from the circular cylinder to the normal flat plate

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