Vortex-induced vibrations of a long flexible circular cylinder

1993 ◽  
Vol 250 ◽  
pp. 481-508 ◽  
Author(s):  
D. Brika ◽  
A. Laneville
Keyword(s):  
Circular Cylinder ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Abrupt Change ◽  
Velocity Range ◽  
End Effects ◽  
Synchronization Region ◽  
Vortex Induced Vibrations ◽  
Set Up ◽  
Vortex Shedding Modes

In an experimental study of the vortex-induced oscillations of a long flexible circular cylinder, the observed stationary amplitudes describe an hysteresis loop partially different from earlier studies. Each branch of the loop is associated with a vortex shedding mode and, as a jump from one branch to the other occurs, the phase difference between the cylinder displacement and the vortex shedding undergoes an abrupt change. The critical flow velocities at which the jump occurs concur with the flow visualization observations of Williamson & Roshko (1988) on the vortex shedding modes near the fundamental synchronization region. Impulsive regimes, obtained at a given flow velocity with the cylinder initially at rest or pre-excited, and progressive regimes resulting from a variation of the flow velocity, are examined. The occurrence of bifurcations is detected for a flow velocity range in the case of the impulsive regimes. The coordinates of the bifurcations define a boundary between two vortex shedding modes, a boundary that verifies the critical curve obtained by Williamson & Roshko (1988). The experimental set-up of this study simulates half the wavelength of a vibrating cable, eliminates the end effects present in oscillating rigid cylinder set-up and has one of the lowest damping ratios reported for the study of this phenomenon.

Vortex-induced vibrations of a circular cylinder at low Reynolds numbers

2007 ◽  
Vol 594 ◽  
pp. 463-491 ◽  
Author(s):  
T. K. PRASANTH ◽  
S. MITTAL
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Free Vibrations ◽  
Forced Vibrations ◽  
Two Dimensions ◽  
Element Formulation ◽  
Transverse Displacement ◽  
Mean Flow ◽  
Phase Jump ◽  
Vortex Induced Vibrations

Results are presented for a numerical simulation of vortex-induced vibrations of a circular cylinder of low non-dimensional mass (m* = 10) in the laminar flow regime (60 < Re < 200). The natural structural frequency of the oscillator, fN, matches the vortex shedding frequency for a stationary cylinder at Re = 100. This corresponds to fND2/ν = 16.6, where D is the diameter of the cylinder and ν the coefficient of viscosity of the fluid. A stabilized space–time finite element formulation is utilized to solve the incompressible flow equations in primitive variables form in two dimensions. Unlike at high Re, where the cylinder response is known to be associated with three branches, at low Re only two branches are identified: ‘initial’ and ‘lower’. For a blockage of 2.5% and less the onset of synchronization, in the lower Re range, is accompanied by an intermittent switching between two modes with vortex shedding occurring at different frequencies. With higher blockage the jump from the initial to lower branch is hysteretic. Results from free vibrations are compared to the data from experiments for forced vibrations reported earlier. Excellent agreement is observed for the critical amplitude required for the onset of synchronization. The comparison brings out the possibility of hysteresis in forced vibrations. The phase difference between the lift force and transverse displacement shows a jump of almost 180° at, approximately, the middle of the synchronization region. This jump is not hysteretic and it is not associated with any radical change in the vortex shedding pattern. Instead, it is caused by changes in the location and value of the maximum suction on the lower and upper surface of the cylinder. This is observed clearly by comparing the time-averaged flow for a vibrating cylinder for different Re. While the mean flow for Re beyond the phase jump is similar to that for a stationary cylinder, it is associated with a pair of counter-rotating vortices in the near wake for Re prior to the phase jump. The phase jump appears to be one of the mechanisms of the oscillator to self-limit its vibration amplitude.

Numerical Simulation of Vortex Shedding Past a Circular Cylinder in a Cross-Flow at Low Reynolds Number With Finite Volume Technique: Part 2 — Flow-Induced Vibration

2007 ◽  
Author(s):  
Antoine Placzek ◽  
Jean-Franc¸ois Sigrist ◽  
Aziz Hamdouni
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Time Integration ◽  
Cross Flow ◽  
Forced Oscillations ◽  
Turbulent Regime ◽  
Flow Induced Vibration ◽  
Coupling Procedure ◽  
Vortex Shedding Modes ◽  
Good Agreement

This paper is the sequel of the work exposed in a companion publication dealing with forced oscillations of a circular cylinder in a cross-flow. In the present study, oscillations of the cylinder are now directly induced by the vortex shedding process in the wake and therefore, the former model used for forced oscillations has been modified to take into account the effects of the flow in order to predict the displacement of the cylinder. The time integration of the cylinder motion is performed with an explicit staggered algorithm whose numerical damping is low. In the first part of the paper, the performances of the coupling procedure are evaluated in the case of a cylinder oscillating in a confined configuration for a viscous flow. Amplitude and frequency responses of the cylinder in a cross-flow are then investigated for different reduced velocities U* ranging from 3 to about 15. The results show a very good agreement at Re = 100 and the vortex shedding modes have also been related to the frequency response observed. Finally, some perspectives for further simulations in the turbulent regime (at Re = 1000) with structural damping are presented.

Locked-on vortex shedding modes from a rotationally oscillating circular cylinder

2017 ◽  
Vol 146 ◽  
pp. 324-338 ◽  
Author(s):  
H.V.R. Mittal ◽  
Qasem M. Al-Mdallal ◽  
Rajendra K. Ray
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Vortex Shedding Modes

Vortex-Induced Vibrations of a Flexible Cylinder in a Slowly Varying Flow: Experimental Results

2002 ◽  
Author(s):  
Fre´de´ric Lague¨ ◽  
Andre´ Laneville
Keyword(s):  
Wind Tunnel ◽  
Flow Velocity ◽  
Wind Velocity ◽  
Vortex Shedding ◽  
Large Scale ◽  
Critical Curve ◽  
Wave Form ◽  
Flexible Cylinder ◽  
Flexible Tube ◽  
Vortex Induced Vibrations

This paper deals with a wind tunnel simulation of the vortex-induced vibrations of a long flexible cylinder in cross-flow when the flow velocity varies periodically with different low frequencies and different flow velocity amplitude. The experimental set-up consists of a flexible tube suspended at the nodes of its first free-free mode of vibration. In order to modulate the wind velocity, the fan rpm of the wind tunnel is controlled: this simulation allows the excursions and incursions in the region of lock-in as well as the periodical crossing of the critical curve separating the 2S and 2P modes of vortex shedding. The additional objective of the simulation is to reproduce more closely the behavior of aerial conductor in the fields and exposed to large scale and low frequency “turbulence”. The results show that the amplitude of vibrations of the flexible tube is modulated with the frequency of the periodic wind fluctuations: it can range from a simple beating to chaotic fluctuations superimposed to a mean. The amplitude of vibrations, when compared to the case of steady wind velocity, may decrease or increase according to the range of the wind mean velocity. Modulation taking different shapes is observed: it may adopt a wave form made of “sharp” peaks or “smooth” periodic oscillations or a combination of the two; sometimes it may be of chaotic form. A link is established between the “sharp” peaks, the occurrence of bifurcations, the presence of the two modes of vortex shedding and the critical curve. The instantaneous amplitude of vibrations is observed to exceed that measured under steady flow conditions.

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.

POD ANALYSIS OF THREE-DIMENSIONAL HARMONICALLY FORCED WAKE FLOW OF A CIRCULAR CYLINDER

2015 ◽  
Vol 39 (4) ◽  
pp. 789-803 ◽  
Author(s):  
Negar Nabatian ◽  
Xiaofei Xu ◽  
Njuki Mureithi
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Transverse Velocity ◽  
Lift Coefficient ◽  
Oscillation Amplitude ◽  
Three Dimensional ◽  
Wake Flow ◽  
Cylinder Wake ◽  
Pod Analysis ◽  
Vortex Shedding Modes

A 3D numerical simulation of a circular cylinder wake is presented in this paper. The cylinder is harmonically forced in the stream-wise direction. The objective of the present work is to investigate the effect of the oscillation amplitude on the secondary transition of the wake. The frequency of the lift force is then linked to the form of the vortex shedding mode. The relation between these vortex shedding modes using POD analysis of the transverse velocity and the unsteady lift coefficient of 3D simulation is in good agreement with the 2D model. Results show that the 3D spanwise effect, which can change the wake structure, is suppressed at Re = 200 by streamwise oscillation of the cylinder. Thus the 2D analysis can effectively model the temporal instability of the wake flow.

Evolution of unstable system.

2015 ◽  
Vol 9 (3) ◽  
pp. 2487-2502 ◽  
Author(s):  
Igor V. Lebed
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Stokes Flow ◽  
Stable Solution ◽  
The State ◽  
Unstable System ◽  
Unstable Flow ◽  
Unstable Solutions ◽  
Vortex Shedding Modes ◽  
Hydrodynamics Equations

Scenario of appearance and development of instability in problem of a flow around a solid sphere at rest is discussed. The scenario was created by solutions to the multimoment hydrodynamics equations, which were applied to investigate the unstable phenomena. These solutions allow interpreting Stokes flow, periodic pulsations of the recirculating zone in the wake behind the sphere, the phenomenon of vortex shedding observed experimentally. In accordance with the scenario, system loses its stability when entropy outflow through surface confining the system cannot be compensated by entropy produced within the system. The system does not find a new stable position after losing its stability, that is, the system remains further unstable. As Reynolds number grows, one unstable flow regime is replaced by another. The replacement is governed tendency of the system to discover fastest path to depart from the state of statistical equilibrium. This striving, however, does not lead the system to disintegration. Periodically, reverse solutions to the multimoment hydrodynamics equations change the nature of evolution and guide the unstable system in a highly unlikely direction. In case of unstable system, unlikely path meets the direction of approaching the state of statistical equilibrium. Such behavior of the system contradicts the scenario created by solutions to the classic hydrodynamics equations. Unstable solutions to the classic hydrodynamics equations are not fairly prolonged along time to interpret experiment. Stable solutions satisfactorily reproduce all observed stable medium states. As Reynolds number grows one stable solution is replaced by another. They are, however, incapable of reproducing any of unstable regimes recorded experimentally. In particular, stable solutions to the classic hydrodynamics equations cannot put anything in correspondence to any of observed vortex shedding modes. In accordance with our interpretation, the reason for this isthe classic hydrodynamics equations themselves.

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