A highly accurate fourierchebyshev spectral collocation method has been used to simulate flow in the wake of a sphere in the reynolds number range from 350 to 650. The emphasis in this monograph is on the classical theory of inviscid incompressible fluids containing finite regions of vorticity. Numerical assessment of wake dynamics and vortex shedding. The diameter ratio of the main cylinder and the wire equals dd50 so no vortex shedding is expected to occur for the wire. American institute of aeronautics and astronautics 12700 sunrise valley drive, suite 200 reston, va 201915807 703. Vortex dynamics in the wake of a cylinder springerlink. Dynamics and flow structures in the turbulent wake of rigid.
The dynamics of vortex streets in channels xiaolinwang1,2, aandsilasalben1. Vortex suppression and drag reduction in the wake of. The flow visualization images and sketches by williamson 1992 suggest that the essential features of the wake vortex dynamics may be described by these two frequencies. An analysis of the vortex dynamics in the wake of three different freestream turbine concepts is conducted to gain a better understanding of the main processes affecting the energy recovery in their wakes. Vortex dynamics of a cylinder wake in proximity to a wall. Vortex dynamics in the wake 479 view of a vortex street in cross section is shown in figure 1, where regions of concentrated vorticity are shed into the downstream flow from alternate sides of the body and with alternate senses of rotation, giving the appearance of an upper row of negative vortices and lower row of positive vortices. The uid dynamics video presented in this investigation is used to illustrate the e ect of aspect ratio on dual step cylinder wake development for re d 2100, dd 2, and 0. Flowinduced vibration fiv is an important phenomenon, by which the flow around bluff bodies creates forces that excite vibration. Energy contents and vortex dynamics in modec transition. Analyzing threedimensional wake vortex dynamics using. Realtime identification of vortex shedding in the wake of a. Oblique and parallel modes of vortex shedding in the wake of a circular cylinder at low reynolds numbers chk williamson journal of fluid mechanics 206, 579627, 1989. Energy contents and vortex dynamics in modec transition of.
The maximum decrement occurs at a wire position of y wd0. Threedimensional vortex structures in a cylinder wake. Centreville, montreal, qc, canada, h3c 3a7 abstract the vortex wake flow dynamics downstream of a cylinder. The flow topology between the gaps of triangular cylinders at various reynolds numbers and centretocentre distances remain elusive. Vortex dislocation mechanisms in the near wake of a step. The effects of crossflow oscillation of a cylinder on the formation of vortices in its wake are investigated experimentally by means of flowvisualization studies in a 4. Resolving vortexinduced pressure fluctuations on a cylinder. Detecting vortex formation and shedding in cylinder wakes. Vortex dynamics in the cylinder wake semantic scholar. May, 2019 the interaction between rotor wake and a cylinder has been studied experimentally in the current work. As a generalization of foppls flow past a circular cylinder 5, a steady solution is given for flow past an elliptical cylinder of arbitrary aspect ratio perpendicular or parallel to the flow at infinity with a bound wake of two symmetric recirculating eddies in the form of a. Secondary vortex dynamics in the cylinder wake during laminarto.
Vortex shedding in the wake of a dual step cylinder. Vortex dynamics is a natural paradigm for the field of chaotic motion and modern dynamical system theory. A vortex street will form only at a certain range of flow velocities, specified by a range of reynolds numbers re, typically above a limiting re value of about 90. Zovatto and pedrizzetti35 studied the vortex wake pattern of a cylinder placed asymmetrically in the channel and showed that the vortex wake.
Vorticity dynamics in the wake of a yawed cylinder fluids. The threedimensional 3d, timedependent, incompressible navierstokes. As with most fluid dynamics phenomena, the physics of vortexinduced vibrations is quite rich and very complicated. Pdf simulation of vortex dynamics in a cylinder wake by the. In part i, steady wakes in inviscid fluid are constructed and investigated using the techniques of vortex dynamics. A detailed analysis of cylinder wake dynamics is presented for characteristic instabilities spanning laminartoturbulent transition regimes. Additionally, the motion of the object in the fluid affects the formation andor shedding of vortices and can have a positive or. The typical reynolds number for insect flight is in the range of 100, where both the viscous and inertial forces are relevant. We investigate numerically vortexinduced vibrations viv of two identical twodimensional elastically mounted cylinders in tandem in the proximitywake interference regime at reynolds number re 200 for systems having both one transverse vibrations and two transverse and inline degrees of freedom 1dof and 2dof, respectively. At low reynolds numbers based on cylinder diameter re47 an unsteady wake develops behind the circular cylinder due to instabilities in the separation bubble that.
Vortex dynamics analysis we now proceed to describe the changes in vortex wake modes as a function of cylinder oscillation amplitude. Analyzing threedimensional wake vortex dynamics using time. Pdf vortex dynamics for flow over a circular cylinder in proximity to. Modelbased estimation of vortex shedding in an unsteady. Largeeddy simulations les are used to investigate the modifications of wake dynamics and turbulence characteristics behind a circular cylinder placed near a wall for varying gaptodiameter gd ratios where g signifies the gap between the wall and the cylinder, and d the cylinder diameter. Howeveraboutre 50 the width of the wake approaches the. Lift frequency effect for each simulation, the steady state lift frequency or the last 5000 time steps in case of non periodic response is. The crossstream vorticity is observed to shed from the cylinder as thin sheets and to wrap around the ka.
On the relationship between the vortex formation process. Mureithi bwcaeclnserc chair of fluidstructure interaction department of mechanical engineering ecole polytechnique box 6079, succ. Pdf simulation of vortex dynamics in a cylinder wake by. On the relationship between the vortex formation process and cylinder wake vortex patterns by david jeonand morteza gharib graduate aeronautical laboratory, california institute of technology, pasadena, ca 91125, usa received 10 july 2004 and in revised form 12 july 2004 the idea of vortex formation time, originally developed for vortex ring. Resolving vortexinduced pressure fluctuations on a. Vortex shedding in air harvard natural sciences lecture. Andersson skip to main content accessibility help we use cookies to distinguish you from other users and to provide you with a better experience on our websites. The secondary effect of the wire is observed in the kinematics of. Realtime identification of vortex shedding in the wake of. The study is performed using planar high framerate particle image velocimetry.
On the vortex dynamics in the wake of a finite surface. Vortexinduced vibrations of two cylinders in tandem. The 3d nature of turbulent flow causes phase shift in the spanwise direction. Vortex dislocation mechanisms in the near wake of a step cylinder volume 891 cai tian, fengjian jiang, bjornar pettersen, helge i. Vortex and wake induced vibrations in an array of cylinders. Bluff body wake flows have direct engineering significance.
They showed that any perturbation in a vortex line or tube in the separating shear layer can magnify, under the action of selfinduction and stretching induced by the karman vortices, into riblike vortices in the braid joining consecutive karman vortices. Iii discusses the numerical method for solving the model, sec. A dualstep cylinder is comprised of a large diameter cylinder d with low aspect ratio ld attached coaxially to the midspan of a small diameter cylinder d. We present simulation results of vortexinduced vibrations of an infinitely long flexible cylinder at reynolds number re, corresponding to a young turbulent wake i. Threedimensional vortex dynamics in bluff body wakes. However, little attention has been paid to the dynamics and. Vortex dynamics in the cylinder wake williamson, c h k 19960101 00. The fluid dynamics video presented in this investigation is used to illustrate the effect of aspect ratio on dual step cylinder wake development for re 2100, dd 2, and 0. Pdf vortex dynamics in the sphere wake researchgate. Computational fluid dynamics and vortex dynamics research. Dec 14, 2011 the shedding process in the near wake of a surfacemounted, square crosssection cylinder of heighttowidth aspect ratio 4 at a reynolds number of 12,000 based on freestream velocity and the obstacle width was investigated. However, these studies are based on single triangular cylinder only. Computational fluid dynamics and vortex dynamics the interaction between flapping wings and unsteady flows is governed by the navierstokes equation coupled to the dynamic boundaries.
When marine risers are designed in a tandem arrangement, two aspects of fiv including vortex induced vibration viv and wake induced vibration wiv are very important, resulting in strong vibrations and fatigue damage. Flow visualizations and frequency spectra provide a glimpse of the complex vortex dynamics that are observed in the sphere wake. The effects of viscosity, compressiblity, inhomogeneity, and stratification are enormously important in many. The gap flow is able to periodically force either the top or the bottom shear layer of the front cylinder into the gap region, setting off a series of very complex vortex to vortex and vortex to cylinder interactions, which induces pressure gradients that result in a large oscillatory force in phase with the vortex shedding and lead to the. Pdf vortex dynamics in a wiredisturbed cylinder wake. For example, various vortex wake modes are possible with fluid flow jumping from one mode to another. The shedding process in the near wake of a surfacemounted, square crosssection cylinder of heighttowidth aspect ratio 4 at a reynolds number of 12,000 based on freestream velocity and the obstacle width was investigated. The global reynolds number for a flow is a measure of the ratio of inertial to viscous forces in the flow of a fluid around a body or in a channel, and may be defined as a nondimensional parameter of the global speed of the. The primary effect of the wire is the reduction of the. Furthermore, parezanovic and cadot20,21 characterized the modi. Vortex suppression and drag reduction in the wake of counter. Introduction the wake behind a circular cylinder is a canonical ow that has implications in the control of vortex shedding from a arietvy of blu bodies.
Vortex dynamics in the wake of three generic types of. Vortex dynamics in the cylinder wake vortex dynamics in the cylinder wake williamson, c h k 19960101 00. Ivstudies the effects of fluid parameters on vortex dynamics, and the conclusions follow in sec. The celerity of the positive vortex shed from the lower side of the cylinder was smaller than that of the upper side shed vortex due.
Vorticity dynamics in the wake of a yawed cylinder. The aim of this work is to examine wake dynamics and vortex. Plasmabased actuators for cylinder wake vortex control. Iidescribes the model for the vortex dynamics, sec. Dynamics and flow structures in the turbulent wake of. However, the vorticity introduced by the wire in the vicinity of the upper shear layer of the cylinder still affects the vortex dynamics in the wake of the main cylinder. Zdrakovich 15, 16 summarized most of the well known findings related to the flow past a circular cylinder. Cylinder wake dynamics in the presence of streamwise. Jun 20, 2012 american institute of aeronautics and astronautics 12700 sunrise valley drive, suite 200 reston, va 201915807 703. Stability and bifurcation analysis of a forced cylinder wake. The simulations are based on a new class of spectral methods suitable for unstructured and hybrid grids. Simulation of vortex dynamics in a cylinder wake by the immersed boundary technique article pdf available in progress in computational fluid dynamics an international journal 103. Vortex formation in the wake of an oscillating cylinder.
Oct 24, 2017 an analysis of the vortex dynamics in the wake of three different freestream turbine concepts is conducted to gain a better understanding of the main processes affecting the energy recovery in their wakes. Simulation of plate in free fall carried out by using a cutcell method mittal et al. Vortex dislocation mechanisms in the near wake of a step cylinder. The vortex dislocations occur periodically, and are linked to two dominant frequencies detectable in the large cylinder wake. Looking at the wake flow in terms of the vortex wake mode behind the cylinder the strong effect of the cylinder motion is apparent. Vortex shedding in the wake of a dual step cylinder arxiv. Furthermore, parezanovic and cadot 20,21 characterized the modi. The interaction between rotor wake and a cylinder has been studied experimentally in the current work. An increase in streamwise and transverse reorientation of spanwise vorticity is identified for increasing re, leading to a decrease of up to 20% in. Largeeddy simulations les are used to investigate the modifications of wake dynamics and turbulence characteristics behind a circular cylinder placed near a. A number of past experimental studies involving circular cylinders have focused on various flow problems, including aeroacoustics 14, spanwise correlation 15, vortex and wake dynamics 16, 17, and drag reduction 14. Between 5 the steady attached vortices that form the wake behind the cylindergrow withre. Ijrras 11 3 june 2012 varshney vortex structures in the wake of inclined cylinders 478 fig.
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