Wake Topology of a Cylinder Undergoing Vortex-Induced Vibrations With Elliptic Trajectories

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Sina Kheirkhah ◽  
Serhiy Yarusevych ◽  
Sriram Narasimhan
Keyword(s):  
Vortex Shedding ◽  
Vortex Dynamics ◽  
Vortex Formation ◽  
Wake Vortex ◽  
Incoming Flow ◽  
Mass Ratio ◽  
Formation Region ◽  
Vortex Pairs ◽  
Vortex Induced Vibrations ◽  
Spanwise Vortex

Wake vortex shedding topology of a cylinder undergoing vortex-induced vibrations (VIV) is investigated experimentally. Vibration measurements and flow visualization are utilized to study the connection between the cylinder response and the wake topology. The experiments were performed for two different orientations of the elliptic trajectories relative to the incoming flow at a fixed Reynolds number, moment of inertia ratio, mass ratio, and reduced velocity. Similar to the classical 2P regime, two counter-rotating vortex pairs are produced per oscillating cycle for both cases of elliptic trajectories examined here. However, significant changes in wake vortex dynamics are observed along the cylinder span. These changes include merging of vortices, which leads to shedding patterns similar to 2S and P + S modes downstream of the vortex formation region. The observed changes in vortex dynamics are accompanied by splitting of spanwise vortex filament and are attributed primarily to the changes in the local amplitude of vibrations along the span of the pivoted cylinder. It is shown that, being dependent on both the local amplitude of vibrations and vortex dynamics, the observed wake topology cannot be captured by the classical map of shedding regimes developed for VIV of one degree-of-freedom (DOF) cylinders.

The effect of a bevelled trailing edge on vortex shedding and vibration

1973 ◽  
Vol 61 (2) ◽  
pp. 323-335 ◽  
Author(s):  
M. E. Greenway ◽  
C. J. Wood
Keyword(s):  
Vortex Shedding ◽  
Vortex Formation ◽  
Steady Motion ◽  
Visualization Technique ◽  
Rapid Decay ◽  
Formation Region ◽  
Towing Tank ◽  
Excited Vibration ◽  
Trailing Edges ◽  
Circulation Distribution

Experiments using a wind tunnel and a flow visualization technique in a towing tank were conducted to investigate the mechanism of vortex shedding from bevelled trailing edges. These reveal an important difference between the wake structures generated by heaving and steady motion. The suppression of vortex-excited vibration by means of bevelled trailing edges is attributed to the intermittency and rapid decay of the vortex trail resulting from an asymmetric circulation distribution in the vortex formation region.

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.

Symmetric Vortex Shedding From a Circular Cylinder Under Periodic Flow Forcing

2006 ◽  
Author(s):  
E. Konstantinidis ◽  
S. Balabani
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Excitation Frequency ◽  
Symmetric Mode ◽  
Near Wake ◽  
Wake Field ◽  
Vortex Pairs ◽  
Probabilistic Function ◽  
Number Of Cycles

This paper describes an experimental study of the near wake of a circular cylinder subjected to streamwise flow forcing. The wake field is examined by PIV and LDV for excitation frequencies in which symmetric shedding is likely. The results show that symmetric formation of vortex pairs occurs close to the cylinder synchronized with the oscillatory component of the flow. The symmetric mode rapidly breaks down and gives rise to an antisymmetric arrangement of single vortices further downstream. The number of cycles for which the symmetrical vortices persist in the near wake is a probabilistic function of the excitation frequency and forcing amplitude. Details of the related wake kinematics and frequencies are shown and the findings are discussed in relation to symmetric vortex formation occurring in self-excited streamwise oscillations.

scholarly journals A parametric study of energy extraction from vortex-induced vibrations

2018 ◽  
Vol 42 (4) ◽  
pp. 359-369
Author(s):  
Olivier Paré-Lambert ◽  
Mathieu Olivier
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Maximum Efficiency ◽  
Mass Ratio ◽  
Parametric Space ◽  
Turbine Performance ◽  
Vortex Induced Vibrations ◽  
Mass Ratios ◽  
Low Mass ◽  
Wake Modes

This paper presents a parametric investigation of an oscillating-cylinder turbine concept based on vortex-induced vibrations. The parametric space includes four parameters: the Reynolds number, the mass ratio, the dimensionless stiffness, and the dimensionless damping. The damping–stiffness space is explored for four different mass ratios at a fixed Reynolds number of 200. Also, the influence of the parameters on the amplitude of cylinder displacement and on the efficiency of power harnessing is discussed. Vortex-shedding patterns observed within the parametric space are investigated. The 2S, 2P, and C(2S) wake modes are observed and are related to turbine performance. Preliminary results show a maximum efficiency of 10.6%, which is obtained with low mass ratios.

Airfoil Vibration Due to Upstream Alternating Vortices Generated by a Circular Cylinder

2002 ◽  
Author(s):  
K. F. Luk ◽  
R. M. C. So ◽  
S. C. Kot ◽  
Y. L. Lau ◽  
R. C. K. Leung
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Dynamic Responses ◽  
Laser Vibrometer ◽  
Flow Induced Vibration ◽  
Formation Region ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Rapid Drop

An experimental investigation of airfoil vibration due to upstream alternating vortices was carried out in a re-circulating wind tunnel. A circular cylinder with a diameter D = 102mm was positioned upstream of an airfoil (NACA0012), with a chord length c = 200mm and a zero angle of attack placed at a gap distance S, to generate the vortex street. The circular cylinder and airfoil were arranged in tandem and the spacing ratio S/D was varied from 0.5 to 6.5 to investigate the effect of the vortices generated upstream on the vibration of the airfoil. The experiment was carried out in a free stream Re range of 1.6×105 to 2.3×105. The vortex formation region behind a single circular cylinder was measured using a hot wire anemometer and the airfoil dynamic responses were examined using a laser vibrometer. It is found that when S/D is reduced beyond a critical value, there is a rapid drop in vortex shedding frequency and a suppression in airfoil vibration. This critical S/D is found to be the normalized length of the vortex formation region behind the single cylinder. It is hypothesized that the vortex could not be formed at this location within the gap distance in the presence of the airfoil, but instead is formed behind the airfoil. Consequently, as vortex shedding is switched from upstream to downstream of the airfoil, the flow-induced vibration of the airfoil is suppressed at the same time.

scholarly journals The Effect of Slat Opening on Vortex Shedding Behind a Circular Cylinder

2019 ◽  
Vol 8 (4) ◽  
pp. 6879-6885
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Governing Equation ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Bluff Bodies ◽  
Vortex Induced Vibrations ◽  
Better Than ◽  
Laminar Model

Add-on devices are widely used as one of the means of suppressing vortex induced vibrations from bluff bodies. The present study numerically investigates flow over a circular cylinder attached by an axial slat. The axial slat were of uniform and non-uniform openings of 67% and 44% porosity. The governing equation was solved using viscous-laminar model at Reynolds number, Re=300. It was found that the presence of the axial slats significantly suppressed vortex shedding behind the circular cylinder. The non-uniform slats showed longer vortex formation length with lower drag, in comparison to that of the uniform slats. In addition, the slats with 67% porosity of both uniform and non-uniform openings suppressed vortex better than that of 44% porosity slats, indicated by the longer vortex formation length and weaker intensity of vortices.

Vortex dynamics for flow over a circular cylinder in proximity to a wall

2017 ◽  
Vol 812 ◽  
pp. 698-720 ◽  
Author(s):  
Guo-Sheng He ◽  
Jin-Jun Wang ◽  
Chong Pan ◽  
Li-Hao Feng ◽  
Qi Gao ◽  
...  
Keyword(s):  
Circular Cylinder ◽  
Shear Layer ◽  
Flat Plate ◽  
Vortex Shedding ◽  
Vortex Dynamics ◽  
Wake Vortex ◽  
Secondary Vortex ◽  
Cylinder Wake ◽  
Gap Ratio ◽  
Shedding Frequency

The dynamics of vortical structures in flow over a circular cylinder in the vicinity of a flat plate is investigated using particle image velocimetry (PIV). The cylinder is placed above the flat plate with its axis parallel to the wall and normal to the flow direction. The Reynolds number $Re_{D}$ based on the cylinder diameter $D$ is 1072 and the gap $G$ between the cylinder and the flat plate is varied from gap-to-diameter ratio $G/D=0$ to $G/D=3.0$. The flow statistics and vortex dynamics are strongly dependent on the gap ratio $G/D$. Statistics show that as the cylinder comes close to the wall ($G/D\leqslant 2.0$), the cylinder wake becomes more and more asymmetric and a boundary layer separation is induced on the flat plate downstream of the cylinder. The wake vortex shedding frequency increases with decreasing $G/D$ until a critical gap ratio (about $G/D=0.25$) below which the vortex shedding is irregular. The deflection of the gap flow away from the wall and its following interaction with the upper shear layer may be the cause of the higher shedding frequency. The vortex dynamics is investigated based on the phase-averaged flow field and virtual dye visualization in the instantaneous PIV velocity field. It is revealed that when the cylinder is close to the wall ($G/D=2.0$), the cylinder wake vortices can periodically induce secondary spanwise vortices near the wall. As the cylinder approaches the wall ($G/D=1.0$) the secondary vortex can directly interact with the lower wake vortex, and a further approaching of the cylinder ($G/D=0.5$) can result in more complex interactions among the secondary vortex, the lower wake vortex and the upper wake vortex. The breakdown of vortices into filamentary debris during vortex interactions is clearly revealed by the coloured virtual dye visualizations. For $G/D<0.25$, the lower shear layer is strongly inhibited and only the upper shear layer can shed vortices. Investigation of the vortex formation, evolution and interaction in the flow promotes the understanding of the flow physics for different gap ratios.

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.

scholarly journals Vortex-induced vibrations of a long flexible cylinder in shear flow

2011 ◽  
Vol 677 ◽  
pp. 342-382 ◽  
Author(s):  
REMI BOURGUET ◽  
GEORGE E. KARNIADAKIS ◽  
MICHAEL S. TRIANTAFYLLOU
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Maximum Velocity ◽  
Travelling Wave ◽  
Transition To Turbulence ◽  
Wave Component ◽  
Flexible Cylinder ◽  
Vortex Induced Vibrations ◽  
Lock In

We investigate the in-line and cross-flow vortex-induced vibrations of a long cylindrical tensioned beam, with length to diameter ratio L/D = 200, placed within a linearly sheared oncoming flow, using three-dimensional direct numerical simulation. The study is conducted at three Reynolds numbers, from 110 to 1100 based on maximum velocity, so as to include the transition to turbulence in the wake. The selected tension and bending stiffness lead to high-wavenumber vibrations, similar to those encountered in long ocean structures. The resulting vortex-induced vibrations consist of a mixture of standing and travelling wave patterns in both the in-line and cross-flow directions; the travelling wave component is preferentially oriented from high to low velocity regions. The in-line and cross-flow vibrations have a frequency ratio approximately equal to 2. Lock-in, the phenomenon of self-excited vibrations accompanied by synchronization between the vortex shedding and cross-flow vibration frequencies, occurs in the high-velocity region, extending across 30% or more of the beam length. The occurrence of lock-in disrupts the spanwise regularity of the cellular patterns observed in the wake of stationary cylinders in shear flow. The wake exhibits an oblique vortex shedding pattern, inclined in the direction of the travelling wave component of the cylinder vibrations. Vortex splittings occur between spanwise cells of constant vortex shedding frequency. The flow excites the cylinder under the lock-in condition with a preferential in-line versus cross-flow motion phase difference corresponding to counter-clockwise, figure-eight orbits; but it damps cylinder vibrations in the non-lock-in region. Both mono-frequency and multi-frequency responses may be excited. In the case of multi-frequency response and within the lock-in region, the wake can lock in to different frequencies at various spanwise locations; however, lock-in is a locally mono-frequency event, and hence the flow supplies energy to the structure mainly at the local lock-in frequency.

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