Vortex Formation in the Wake of a Vibrating, Flexible Cable

1974 ◽  
Vol 96 (4) ◽  
pp. 317-322 ◽  
Author(s):  
S. E. Ramberg ◽  
O. M. Griffin
Keyword(s):  
Vortex Shedding ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Hot Wire ◽  
Near Wake ◽  
Formation Region ◽  
Vortex Streets ◽  
Region Length ◽  
Karman Vortex ◽  
Flexible Cables

The von Karman vortex streets formed in the wakes of vibrating, flexible cables were studied using a hot-wire anemometer. All the experiments took place in the flow regime where the vibration and vortex-shedding frequencies lock together, or synchronize, to control the wake formation. Detailed measurements were made of the vortex formation flow for Reynolds numbers between 230 and 650. As in the case of vibrating cylinders, the formation-region length is dependent on a shedding parameter St* related to the natural Strouhal number and the vibrational conditions. Furthermore, the near wake configuration is found to be dependent on the local amplitude of vibration suggesting that the vibrating cylinder rseults are directly applicable in that region.

A note on bluff body vortex formation

1995 ◽  
Vol 284 ◽  
pp. 217-224 ◽  
Author(s):  
Owen M. Griffin
Keyword(s):  
Bluff Body ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Initial Position ◽  
Bluff Bodies ◽  
Near Wake ◽  
Formation Region ◽  
Low Reynolds Numbers ◽  
Region Length ◽  
Low Reynolds

Green & Gerrard (1993) have presented in a recent paper the results of experiments to measure the distribution of vorticity in the near wake of a circular cylinder at low Reynolds numbers (up to Re = 220). They also compared the various definitions of the vortex formation region length which have been proposed by Gerrard (1966), Griffin (1974), and others for both high and low Reynolds numbers. The purpose of this note is to expand the work of Green & Gerrard, and to further their proposition that the end of the vortex formation region at all Reynolds numbers mark both the initial position of the fully shed vortex and the location at which its strength is a maximum. The agreement discussed here between several definitions for the formation region length will allow further understanding to be gained from investigations of the vortex wakes of stationary bluff bodies, and the wakes of oscillating bodies as well.

The vortex street in the wake of a vibrating cylinder

1972 ◽  
Vol 55 (1) ◽  
pp. 31-48 ◽  
Author(s):  
Owen M. Griffin ◽  
Charles W. Votaw
Keyword(s):  
Vortex Breakdown ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Vortex Street ◽  
Fundamental Parameter ◽  
Formation Region ◽  
Von Karman ◽  
Vortex Streets ◽  
Karman Vortex ◽  
Von Kármán

The von Kármán vortex streets formed in the wakes of vibrating smooth cylinders and cables were studied using a hot-wire anemometer and flow visualization by fog injection in a wind tunnel. All the experiments took place in the flow regime where the vibration and vortex-shedding frequencies lock together, or synchronize, to control the formation of the wake. Since the flow in the vortex formation region is fundamental to further understanding of the interaction between a vibrating bluff obstacle and its wake, detailed measurements were made of the formation-region flow for Reynolds numbers between 120 and 350. The formationregion length is shown to be a fundamental parameter for the wake, and is dependent on a shedding parameterSt* related to the natureally occurring Strouhal number for the von Kármán street. The effects of vibration amplitude and frequency on the mean and fluctuating velocity fields in the wake become apparent when the downstream displacement is scaled with the formation length. The von Kármán vortex street behind a vibrating cylinder is divided into three predominant flow regimes: the formation, stable and unstable regions. Fundamental differences exist in the vortex streets generated behind stationary and vibrating cylinders, but many classical characteristics, including the manner of vortex breakdown in the unstable region, are shared by the two systems.

Turbulent vortex streets and the entrainment mechanism of the turbulent wake

1974 ◽  
Vol 62 (1) ◽  
pp. 11-31 ◽  
Author(s):  
Demosthenes D. Papailiou ◽  
Paul S. Lykoudis
Keyword(s):  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Turbulent Wake ◽  
Vortex Street ◽  
Experimental Measurements ◽  
Formation Region ◽  
Turbulent Vortex ◽  
Geometrical Characteristics ◽  
Vortex Streets ◽  
Longitudinal Distance

The results of an experimental investigation of a turbulent vortex street in the range 103 [lsim ] Re [lsim ] 2 × 104 are presented. The vortex street was created by the motion of a circular cylinder in a motionless fluid (mercury). Photographs obtained showed that the turbulent street, created by the vortex shedding behind the cylinder, persisted at longer downstream distances and higher Reynolds numbers than previously reported in the literature. A theory was developed to account for the experimental measurements pertaining to the change of the geometrical characteristics, h (distance between the two rows of vortices) and α (longitudinal distance between two consecutive vortices on the same row), of the street in the downstream direction. The implications of the structure of the vortex street on the entrainment mechanism of the turbulent wake are discussed. Some observations of the flow in the formation region of the vortices are discussed in relation to existing work.

Effects of sound on separated flows

1969 ◽  
Vol 37 (2) ◽  
pp. 265-287 ◽  
Author(s):  
Jon A. Peterka ◽  
Peter D. Richardson
Keyword(s):  
Heat Transfer ◽  
Shear Layer ◽  
Vortex Breakdown ◽  
Vortex Formation ◽  
Cross Flow ◽  
Sound Field ◽  
Reynolds Numbers ◽  
Shear Layers ◽  
Formation Region ◽  
Region Length

Measurements of flow and fluctuating heat transfer were made for a circular cylinder in cross-flow with a transverse standing sound field imposed simultaneously. Reynolds numbers were of the order of 104, known to be in the disturbance-sensitive range, and sound intensities were as large as 140 db. The frequencies of the sound field were of the order of the disturbance frequency in the separated shear layers, reported first by Bloor.With a sound field having its frequency matched sufficiently closely to that occurring naturally in the shear layer, the growth of the instability is enhanced with the processes of vortex fusion and possibly vortex breakdown being detectable. At the same time, the vortex street frequency is only very weakly affected, although the vortex formation region length is reduced when the instability in the shear layer is enhanced. It is suggested that the discretization of vorticity in the shear layers is one factor significant in reducing the formation length. Heat transfer at the rear of the cylinder fluctuates at frequencies centred on the shedding frequency. The fluctuation level increases as the formation region shortens.

Vorticity measurements in the near wake of a circular cylinder at low Reynolds numbers

1993 ◽  
Vol 246 ◽  
pp. 675-691 ◽  
Author(s):  
R. B. Green ◽  
J. H. Gerrard
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Near Wake ◽  
Low Reynolds Numbers ◽  
Region Length ◽  
Low Reynolds ◽  
Definition Of

The technique of the particle streak method has been applied to the study of bluff-body wakes at low Reynolds number. Vorticity and shear stress were measured to an accuracy of 15–20%. The vortex shedding cycles at Reynolds number of 73 and 226 are shown and the differences between the two are highlighted. Quantitative descriptions of the previously described vortex splitting phenomenon in the near wake are made, which leads to a description of the vortex shedding mechanism at low Reynolds number. The definition of low-Reynolds-number formation region length is examined. The strength of shed vortices obtained from integration of the vorticity is compared with directly measured vortex strengths and with the results of two-dimensional numerical analysis.

Velocity Correlation and Vortex Spacing in the Wake of a Vibrating Cable

1976 ◽  
Vol 98 (1) ◽  
pp. 10-18 ◽  
Author(s):  
S. E. Ramberg ◽  
O. M. Griffin
Keyword(s):  
Reynolds Numbers ◽  
Longitudinal Vortex ◽  
Velocity Correlation ◽  
Vortex Streets ◽  
Karman Vortex ◽  
Cross Correlations ◽  
Lock In ◽  
Flexible Cables ◽  
Synchronized Region ◽  
Approach Unity

The von Karman vortex streets formed in the wakes of vibrating, flexible cables were studied using hot wire anemometers. The experiments took place in or at the boundaries of the flow regime where the vibration and vortex-shedding frequencies lock together, or synchronize, to control the wake formation. Spacial cross-correlations of the wake velocity signals were made for Reynolds numbers between 400 and 1300. Within the synchronized region, the magnitude of the measured spanwise cross-correlation coefficient is seen to approach unity, being limited by turbulence but apparently independent of frequency, amplitude, and Reynolds number. The bounds of the lock-in regime are determined and compare remarkably well with previous vibrating, rigid cylinder results. Further, the downstream longitudinal vortex spacing and induced street velocity are also found to compare well with vibrating cylinder results.

The Near Wake Characteristics of Cavitating Bluff Sources

1990 ◽  
Vol 112 (4) ◽  
pp. 492-495 ◽  
Author(s):  
A. S. Ramamurthy ◽  
R. Balachandar
Keyword(s):  
Vortex Shedding ◽  
Vortex Formation ◽  
Cavitation Number ◽  
Test Results ◽  
Near Wake ◽  
Formation Region ◽  
Separation Velocity ◽  
Flow Test ◽  
Velocity Scale ◽  
Wake Characteristics

The influence of cavitation on vortex shedding behind constrained sharp-edged bluff prisms is studied experimentally. At a given blockage, the length of the vortex formation region is found to increase as the cavitation number of the flow is reduced. The vortex appears to be stabilized from breaking up in the partially cavitating regime of flow. Test results indicate that the separation velocity is the proper velocity scale to reduce or eliminate blockage effects.

An Experimental Study on the Vertical Flow Past a Finite-Length Horizontal Cylinder at Low Reynolds Numbers

2014 ◽  
Vol 493 ◽  
pp. 68-73 ◽  
Author(s):  
Willy Stevanus ◽  
Yi Jiun Peter Lin
Keyword(s):  
Finite Length ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Horizontal Cylinder ◽  
Vortex Street ◽  
Vertical Flow ◽  
Low Reynolds Numbers ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The research studies the characteristics of the vertical flow past a finite-length horizontal cylinder at low Reynolds numbers (ReD) from 250 to 1080. The experiments were performed in a vertical closed-loop water tunnel. Flow fields were observed by the particle tracer approach for flow visualization and measured by the Particle Image Velocimetry (P.I.V.) approach for velocity fields. The characteristics of vortex formation in the wake of the finite-length cylinder change at different regions from the tip to the base of it. Near the tip, a pair of vortices in the wake was observed and the size of the vortex increased as the observed section was away from the tip. Around a distance of 3 diameters of the cylinder from its tip, the vortex street in the wake was observed. The characteristics of vortex formation also change with increasing Reynolds numbers. At X/D = -3, a pair of vortices was observed in the wake for ReD = 250, but as the ReD increases the vortex street was observed at the same section. The vortex shedding frequency is analyzed by Fast Fourier Transform (FFT). Experimental results show that the downwash flow affects the vortex shedding frequency even to 5 diameters of the cylinder from its tip. The interaction between the downwash flow and the Von Kármán vortex street in the wake of the cylinder is presented in this paper.

Vortex Shedding from Smooth and Roughened Cylinders in Cross-Flow near a Plane Surface

1979 ◽  
Vol 30 (1) ◽  
pp. 305-321 ◽  
Author(s):  
G. Buresti ◽  
A. Lanciotti
Keyword(s):  
Vortex Shedding ◽  
Plane Surface ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Cylinder Surface ◽  
Hot Wire ◽  
Cylinder Axis ◽  
Supercritical Regime ◽  
Subcritical Regime ◽  
Smooth Cylinder

SummaryThe characteristics of the flow field around a circular cylinder in cross-flow placed at various distances from a plane, parallel both to the flow and to the cylinder axis, were analysed using a hot wire anemometer. Experiments were performed in a wind tunnel with Reynolds numbers ranging from 0.85×105 to 3×105. The spectra of the hot wire signals were obtained using a Fast Fourier Transform technique programmed on a PDP 11/40 computer. As regards a smooth cylinder, the main features of the vortex shedding mechanism in the subcritical regime remained unaltered for distances from the plane greater than approximately 0.4 diameters; in particular the Strouhal frequency did not show any significant variation relative to the typical value for an isolated cylinder. As for lower values of the distance from the plane, the regular vortex shedding disappeared and the hot wire spectra showed typical turbulent features. The possibility of obtaining supercritical conditions by roughening the cylinder surface was confirmed together with the importance of the Reynolds number based on the typical roughness size, Rk, in the evaluation of the flow regime around the cylinder. In the case of roughened cylinders, and with values of Rk below-350, the regular vortex shedding disappeared at a distance from the plane smaller than 0.3 diameters. This fact suggests that, at least in part of the supercritical regime, the influence of the plane can be smaller than in the subcritical regime.

The Orbital Movement and the Damping of the Fluidelastic Vibration of Tube Banks Due to Vortex Formation: Part 2—Criterion for the Fluidelastic Orbital Vibration of Tube Arrays

1974 ◽  
Vol 96 (3) ◽  
pp. 1065-1071
Author(s):  
Y. N. Chen
Keyword(s):  
High Speed ◽  
Vortex Formation ◽  
Vortex Pair ◽  
Free Shear Layer ◽  
Vortex Model ◽  
Speed Flow ◽  
Vortex Streets ◽  
Tube Arrays ◽  
Karman Vortex ◽  
Tube Banks

The phenomenon on the tubes in a tube row, which vibrate alternately along the row in the transverse and stream-wise directions, will be explained by a vortex model. This model consists of the symmetrical vortex pair trains behind the stream-wisely vibrating tubes, and the Karman vortex streets behind the transversely vibrating tubes. It will be shown in the paper that the coupling between these two groups of vortex systems can excite the tube arrays to perform this fluidelastic vibration. A criterion for the onset of this orbital movement will be given with the expression ξ = R/Sxt. This criterion predicts a strong fluidelastic vibration for tubes with low transverse tube spacings and low natural flexible frequencies in a high speed flow. The theory leading to this criterion is based on the phenomenon of the variation in the position of the separation point for the free shear layer during the cylinder vibration. A switching of the jet for maintaining the fluidelastic vibration is then a result of this variation.

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