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Showing papers on "Vortex shedding published in 1993"


Journal ArticleDOI
TL;DR: In this article, an experimental study of the vortex-induced oscillations of a long flexible circular cylinder was performed and the observed stationary amplitudes describe an hysteresis loop partially different from earlier studies.
Abstract: 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.

372 citations


Dissertation
01 Feb 1993
TL;DR: In this article, the authors focus on the measurement, via forced-oscillation experiments, of the vortex-induced lift and drag forces acting on circular cylinders undergoing sinusoidal and amplitude-modulated oscillations.
Abstract: : Vortex-induced forces and consequent vibration of long cylindrical structures are important for a large number of engineering applications, while the complexity of the underlying physical mechanisms is such that this is one of the canonical problems of fluid mechanics Vortex shedding force varies in frequency and magnitude along the length of the structure, causing the response at any point to be amplitude-modulated in space and time The focus is on the measurement, via forced-oscillation experiments, of the vortex-induced lift and drag forces acting on circular cylinders undergoing sinusoidal and amplitude- modulated oscillations Basic concepts on vortex formation and vortex-induced vibrations, a review of the existing literature, and details of the experimental apparatus and data processing methods are presented Stationary and sinusoidal oscillation tests are presented Several novel properties are described, among them the role of the lift force phase angle in causing the amplitude-limited nature of VIV, and use of the lift force excitation region in contrast with the often-quoted but quite different lift force lock-in region Next, a comprehensive data error analysis, and a simple VIV prediction scheme are described New data on amplitude-modulated oscillations are presented The concept of control of the mean wake velocity profile via the control of the major vortical feature is explored, with possible applications being the reduction of the in-line wake velocity and alteration of the wake signature

293 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe experiments undertaken to study in detail the control of vortex shedding from circular cylinders at low Reynolds numbers by using feedback to stabilize the wake instability, and they show that feedback control is able to delay the onset of wake instability by about 20% higher than otherwise.
Abstract: This paper describes experiments undertaken to study in detail the control of vortex shedding from circular cylinders at low Reynolds numbers by using feedback to stabilize the wake instability. Experiments have been performed both in a wind tunnel and in an open water channel with flow visualization. It has been found that feedback control is able to delay the onset of the wake instability, rendering the wake stable at Reynolds numbers about 20% higher than otherwise. At higher flow rates, however, it was not possible to use single-channel feedback to stabilize the wake - although, deceptively, it was possible to reduce the unsteadiness recorded by a near-wake sensor. When control is applied to a long span only the region near the control sensor is controlled. The results presented in this paper generally support the analytical results of other researchers.

263 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compared the results of Ronneberger and Ahrens (1977) with results of linear theory for the propagation of acoustic waves in a pipe with a quiescent fluid.
Abstract: The propagation of plane acoustic waves in smooth pipes and their reflection at open pipe terminations have been studied experimentally. The accuracy of the measurements is determined by comparison of experimental data with results of linear theory for the propagation of acoustic waves in a pipe with a quiescent fluid. The damping and the reflection at an unflanged pipe termination are compared.In the presence of a fully developed turbulent mean flow the measurements of the damping confirm the results of Ronneberger & Ahrens (1977). In the high-frequency limit the quasi-laminar theory of Ronneberger (1975) predicts accurately the convective effects on the damping of acoustic waves. For low frequencies a simple theory combining the rigid-plate model of Ronneberger & Ahrens (1977) with the theoretical approach of Howe (1984) yields a fair prediction of the influence of turbulence on the shear stress. The finite response time of the turbulence near the wall to the acoustic perturbations has to be taken into account in order to explain the experimental data. The model yields a quasi-stationary limit of the damping which does not take into account the fundamental difference between the viscous and thermal dissipation observed for low frequencies.Measurements of the nonlinear behaviour of the reflection properties for unflanged pipe terminations with thin and thick walls in the absence of a mean flow confirm the theory of Disselhorst & van Wijngaarden (1980), for the low-frequency limit. It appears however that a two-dimensional theory such as proposed by Disselhorst & van Wijngaarden (1980) for the high-frequency limit underestimates the acoustical energy absorption by vortex shedding by a factor 2.5.The measured influence of wall thickness on the reflection properties of an open pipe end confirms the linear theory of Ando (1969). In the presence of a mean flow the end correction δ of an unflanged pipe end varies from the value at the high-Strouhal-number limit of δ/a = 0.61, with a the pipe radius, which is close to the value in the absence of a mean flow given by Levine & Schwinger (1948) of δ/a = 0.6133, to a value of δ/a = 0.19 in the low-Strouhal-number limit which is close to the value predicted by Rienstra (1983) of δ/a = 0.26.The pressure reflection coefficient is found to agree with the theoretical predictions by Munt (1977, 1990) and Cargill (1982b) in which a full Kutta condition is included. The accuracy of the theory is fascinating in view of the dramatic simplifications introduced in the theory. For a thick-walled pipe end and a pipe terminated by a horn the end correction behaviour is similar. It is surprising that the nonlinear behaviour at low frequencies and high acoustic amplitudes in the absence of mean flow does not influence the end correction significantly.The aero-acoustic behaviour of the pipe end is dramatially influenced by the presence of a horn. In the presence of a mean flow the horn is a source of sound for a critical range of the Strouhal number.The high accuracy of the experimental data suggests that acoustic measurements can be used for a systematic study of turbulence in unsteady flow and of unsteady flow separation.

226 citations


Journal ArticleDOI
TL;DR: The results of an experimental work concerning the behavior of flows with partial cavities are presented in this article, where a plano-convex foil placed in the free surface channel of the I.M.G.
Abstract: The results of an experimental work concerning the behavior of flows with partial cavities are presented. The tests were carried out using a plano-convex foil placed in the free surface channel of the I.M.G. Hydrodynamic Tunnel. The experimental conditions concerning ambient pressure, water velocity, and body size were such that various and realistic kinds of flows could be realized. The main flow regimes are described and correlated to the values of foil incidence and cavitation parameter. Attention is paid to the shedding of large vapor pockets into the cavity wake and its possible periodic character. Aside from classical consideration to the cavity length and shedding frequency in the periodic regime, results concerning the wall pressure distribution in the rear part of the cavity are given. They lead to distinguish thin, stable, and closed cavities from the thick ones in which the reentrant jet plays a dominant role for the shedding of vortical structures and the flow unsteadiness.

192 citations


Journal ArticleDOI
TL;DR: The physical mechanisms by which the Reynolds shear stress is produced from dynamically evolving vortical structures in the wall region of a direct numerical simulation of turbulent channel flow are explored in this article.
Abstract: The physical mechanisms by which the Reynolds shear stress is produced from dynamically evolving vortical structures in the wall region of a direct numerical simulation of turbulent channel flow are explored. The complete set of quasistreamwise vortices are systematically located and tracked through the flow by the locus of the points of intersection of their centres of rotation with the (y, z) numerical grid planes. This approach assures positive identification of vortices of widely differing strengths, including those whose amplitude changes significantly in time. The process of vortex regeneration, and the means by which vortices grow, distort and interact over time are noted. Ensembles of particle paths arriving on fixed planes in the flow are used to represent the physical processes of displacement and acceleration transport (Bernard & Handler 1990a) from which the Reynolds stress is produced. By interweaving the most dynamically significant of the particle paths with the evolving vortical structures, the dynamical role of the vortices in producing Reynolds stress is exposed. This is found to include ejections of low-speed fluid particles by convecting structures and the acceleration and deceleration of fluid particles in the cores of vortices. Sweep dominated Reynolds stress close to the wall appears to be a manifestation of the regeneration process by which new vortices are created in the flow.

174 citations


Book ChapterDOI
01 Jan 1993
TL;DR: In this paper, the vortex shedding flow past a square cylinder at Re = 22.000 was calculated with various turbulence models and the 2D periodic shedding motion was resolved in an unsteady calculation, and the superimposed stochastic turbulent fluctuations were simulated both with the k-eddy-viscocity model and with a Reynolds-stress equation model.
Abstract: The vortex-shedding flow past a square cylinder at Re = 22.000 was calculated with various turbulence models. The 2D periodic shedding motion was resolved in an unsteady calculation, and the superimposed stochastic turbulent fluctuations were simulated both with the k — e eddy-viscocity model and with a Reynolds-stress equation model. For both models, the viscosity-affected near-wall region was either bridged by wall functions or was resolved with a simpler one-equation model using a prescribed length-scale distribution. The k — e model with wall functions does not yield unsteady vortex motion while the other model variants do. The two-layer k —e model underpredicts severely the periodic fluctuations and also the Strouhal number and drag coefficient. The Reynoldsstress-equation models yield considerably better agreement with experiments, but tend to overpredict the periodic fluctuating motion and also miss some other details of the flow behaviour.

163 citations


Journal ArticleDOI
TL;DR: In this article, a two-dimensional numerical computation was made for unsteady laminar flow in a channel obstructed with a square rod placed perpendicular to the flow in the channel center plane.

129 citations


Journal ArticleDOI
TL;DR: In this paper, the wakes of towed spheres in quiescent baths of glycerin and water mixtures were studied for sphere Reynolds numbers Re in the range 30-4000.
Abstract: The wakes of spheres in a still environment were studied for sphere Reynolds numbers Re in the range 30-4000. The experiments consisted of towed spheres in quiescent baths of glycerin and water mixtures. Measurements included dye traces illuminated by a laser light sheet for visualization and laser velocimetry for streamwise velocities. The recirculation region on the downstream side of the sphere was stable and symmetric for Re 280. Three wake regions were identified: a fast-decay region that was observed only when vortex shedding was present, followed in succession by turbulent and laminar wake regions. Vortex shedding increased the distance to the onset of the turbulent wake region by an order of magnitude due to the presence of the fast-decay wake region. Mean velocities within the turbulent and laminar wake regions scaled according to classical similarity theories, with transition between these regions at conditions where their estimates of mean streamwise velocities along the axis were the same: this occurred at a local wake Reynolds number ReH -10. Within the turbulent wake region, turbulence intensities along the axis were roughly 85% for Rew > 70; however, as the onset of the laminar wake region was approached, turbulence intensities along the axis were proportional to Rew1/4, which is consistent with scaling proposed earlier for the final decay period of axisymmetric wakes.

125 citations


Journal ArticleDOI
TL;DR: In this article, the formation of Karman vortex streets is studied within the framework of single-layer shallow-water dynamics and in absence of surface friction and background rotation, and steady numerical solutions for flow past circular topography were obtained by imposing a symmetry condition that essentially suppressed vortex shedding.
Abstract: The formation of Karman vortex streets is studied within the framework of single-layer shallow-water dynamics and in absence of surface friction and background rotation. In the first part of this study, steady numerical solutions for flow past circular topography were obtained by imposing a symmetry condition that essentially suppressed vortex shedding. In the second part, this symmetry condition is relaxed in order to study the transition into the vortex-shedding regime. This transition is due to an instability of the symmetric wake pattern. The most unstable global normal mode of this instability is derived by a numerical method. Most of the features of this mode can be understood in terms of the absolute instability theory. The mode is essentially barotropic and relies on a positive feedback between the perturbations located on the two shearlines on either side of the wake. The classical shear modes centered on a single shearline are, on the other hand, shown to be absolutely stable even thoug...

103 citations


Journal ArticleDOI
TL;DR: In this article, a wide range of cross-sectional shapes and angles of incidence of prismatic bodies and grids composed of prisms are reviewed for vortex-induced transverse, torsional, streamwise, and plunging vibrations.

Journal ArticleDOI
TL;DR: In this article, the inviscid pressure distribution of Gaster was applied to study the development of a laminar separation bubble, and periodic vortex shedding occurred from the primary separation region.
Abstract: The two‐dimensional unsteady incompressible Navier–Stokes equations, solved by a fractional time‐step method, were used to investigate separation due to the application of an adverse pressure gradient to a low‐Reynolds number boundary layer flow. The inviscid pressure distribution of Gaster [AGARD CP 4, 813 (1966)] was applied in the present computations to study the development of a laminar separation bubble. In all cases studied, periodic vortex shedding occurred from the primary separation region. The shed vortices initially lifted from the boundary layer and then returned towards the surface downstream. The shedding frequency nondimensionalized by the momentum thickness was found to be independent of Reynolds number. The value of the nondimensional Strouhal number, however, was found to differ from the results of Pauley et al. [J. Fluid Mech. 220, 397 (1990)], indicating that the shedding frequency varies with the nondimensional pressure distribution, Cp. The computational results were time averaged o...

Journal ArticleDOI
TL;DR: In this paper, the particle streak method has been applied to the study of bluff-body wakes at low Reynolds number and 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, the authors used flow visualization and two-dimensional Fourier decomposition of velocity measurements to study wakes behind disk-shaped axisymmetric bodies of varying solidity and found that large-scale structures are predominately helical (m = ± 1) and occur at a characteristic frequency which corresponds to their wavelength.
Abstract: Wakes behind disk-shaped axisymmetric bodies of varying solidity are studied using flow visualization and two-dimensional Fourier decomposition of velocity measurements. Evidence of a reverse flow region behind some of the bodies is observed to coincide with the presence of large-scale structures in the near and far wake. Fourier analysis shows that these large-scale structures are predominately helical (m= ±1) and occur at a characteristic frequency which corresponds to their wavelength as observed from flow visualization. Our measured value for this characteristic frequency agrees with vortex shedding frequencies observed for these types of wakes.

Journal ArticleDOI
TL;DR: In this article, the authors explore the structure of streamwise vortices and their interactions with the von Karman Vortices in the immediate wakes of cylinders in a water tunnel at Reynolds numbers from 330-21'000 based on cylinder diameter.
Abstract: Flow‐visualization methods were used to explore the structure of streamwise vortices and their interactions with the von Karman vortices in the immediate wakes of cylinders. The experiments were conducted in a water tunnel at Reynolds numbers from 330–21 000 based on cylinder diameter. Over this entire range of Reynolds number, pairs of counter‐rotating streamwise vortices were observed immediately behind the cylinders, with a mean spanwise spacing of approximately one pair per diameter. The streamwise vortices significantly distorted the von Karman vortices, but only on their upstream‐facing sides. The cylinder near‐surface‐flow topology was found to include a secondary separation line containing ‘‘dominant‐foci structures’’ whose spanwise locations correlated with those of the streamwise vortices.

Journal ArticleDOI
TL;DR: In this article, the temporal development of a 2D viscous incompressible flow generated by a circular cylinder started impulsively into steady rotatory and rectilinear motion is studied by integration of a velocity/vorticity formulation of the governing equations, using an explicit finite-difference/pseudo-spectral technique and an implementation of the Biot-Savart law.
Abstract: The temporal development of a 2D viscous incompressible flow generated by a circular cylinder started impulsively into steady rotatory and rectilinear motion is studied by integration of a velocity/vorticity formulation of the governing equations, using an explicit finite-difference/pseudo-spectral technique and an implementation of the Biot-Savart law. Results are presented for a Reynolds number of 200 (based on the cylinder diameter 2a and the magnitude U of the rectilinear velocity) for several values of the angular/rectilinear speed ratio alpha = omega(a)/U (where omega is the angular speed) up to 3.25. Several aspects of the kinematics and dynamics of the flow not considered earlier are discussed. For higher values of alpha, the results indicate that for Re = 200, vortex shedding does indeed occur for alpha = 3.25. However, consecutive vortices shed by the body can be shed from the same side and be of the same sense, in contrast to the nonrotating case, in which mirror-image vortices of opposite sense are shed alternately on opposite sides of the body. The implications of the results are discussed in relation to the possibility of suppressing vortex shedding by open or closed-loop control of the rotation rate.

Journal ArticleDOI
TL;DR: In this article, experiments were performed to study vortex shedding behind a linearly tapered cylinder, where four cylinders were used, with taper ratios varying from 50:1 to 100:1.
Abstract: Experiments were performed to study vortex shedding behind a linearly tapered cylinder. Four cylinders were used, with taper ratios varying from 50:1 to 100:1. The cylinders were each run at four different velocities, adjusted to cover the range of laminar vortex shedding for a non-tapered cylinder. The flow was confirmed to consist of discrete shedding cells, each with a constant frequency. For a centrespan Reynolds number greater than 100, the dimensionless mean cell length was found to be a constant. Individual cell size was found to be roughly self-similar. New shedding cells were created on the ends of the cylinders, or in regions adjacent to areas not shedding. Successful scalings were found for both the cell shedding frequencies and their differences, the modulation frequencies. The modulation frequencies were found to be constant along the cylinder span. The shedding frequency Strouhal number versus Reynolds number curve was found to have a slightly steeper slope than the Strouhal number curve for a non-tapered cylinder. Vortex shedding was found to begin at a local Reynolds number of about 60, regardless of any other factors. End effects were found to be of little importance.The vortex splits, which form the links between shedding cells, were found to be similar in some respects to those found by earlier investigators. Amplitude results suggested that the splits at different spanwise locations are temporally sequenced by an overall flow mechanism, a supposition confirmed by flow visualization. Wavelet analysis results showed that while the behaviour of the shedding frequencies in time was relatively unaffected by changing taper ratio, the behaviour of the modulation frequency in time was greatly affected. Comparisons with other experiments point out the universality of vortex splitting phenomena.

Journal ArticleDOI
TL;DR: In this paper, a spring-mounted circular cylinder was observed in a wind tunnel and the vertical displacement of the cylinder and velocity fluctuations in the near wake region of a near-wake region were observed.
Abstract: Vortexinduced response of a springmounted circular cylinder was observed in a lowspeed wind tunnel. Vertical (lift) displacement of the cylinder and velocity fluctuations in the near wake region of...

Journal ArticleDOI
TL;DR: In this article, an in-line tube bundle with large spacing ratios is tested in air and water flows to examine the mechanisms of vorticity shedding and acoustic resonance, including correlation measurements of the velocity fluctuations, and visualization of the flow structure at resonant and non-resonant conditions.

Journal ArticleDOI
TL;DR: Water channel flow visualization and anemometry studies were conducted to examine the flow structure and velocity statistics in the wake of a passive mixing tab designed for enhancement of cross-stream mixing by generation of flow structures characteristic of turbulent boundary layers.
Abstract: Water channel flow visualization and anemometry studies were conducted to examine the flow structure and velocity statistics in the wake of a passive mixing tab designed for enhancement of cross-stream mixing by generation of flow structures characteristic of turbulent boundary layers. Flow visualization reveals that the mixing tab generates a wake comprising a combination of counterrotating, streamwise vortices enveloped by distinct hairpin vortex structures

Journal ArticleDOI
TL;DR: In this paper, the topology of the boundary-layer separation line is linked to the subsequent three-dimensional development of the mean and turbulent structures of the wake, and the formation of trailing streamwise vortices behind the nodal points of separation results in a locally narrower wake, a more rapid wake velocity recovery and suppression of the turbulence development within the separated boundary layer.
Abstract: The flowfield behind the wavy-cylinder geometry has been examined using flow visualization, total pressure surveys, and two-component laser Doppler anemometry. The topology of the boundary-layer separation line is linked to the subsequent three-dimensional development of the mean and turbulent structures of the wake. The formation of trailing streamwise vortices behind the nodal points of separation results in a locally narrower wake, a more rapid wake velocity recovery, and suppression of the turbulence development within the separated boundary layer. The dynamic behavior of the trailing vortices suggests that vortex pairing is suppressed by the presence of an axial strain field

Journal ArticleDOI
TL;DR: In this article, the three-dimensional orthogonal spatial modes and their temporal counterparts were extracted from a large-eddy simulation of turbulent flow over a surface-mounted cube, using a space-time symmetric version of proper orthogonality.
Abstract: The three-dimensional orthogonal spatial modes and their temporal counterparts have been extracted from a large-eddy simulation of turbulent flow over a surface-mounted cube, using a space-time symmetric version of proper orthogonal decomposition (POD), proposed by Aubry et al. (1991). A relatively small domain of interest, located immediately above the top face of the flow obstacle, has been selected for the application of POD. Within that volume of interest, time records of the velocity field have been sampled at 6000 locations simultaneously. The space-time duality of POD can be demonstrated by deriving two alternative eigenvalue problems for either the orthogonal spatial modes or the orthogonal temporal modes. For a particular case, the choice between the two alternatives can be done on the basis of computational convenience and of data-storage requirements. The results show that the first spatiotemporal mode can be identified with the mean flow. The second spatiotemporal mode is dominated by the alternating vortex shedding from the side edges of the flow obstacle. A Fourier analysis of the second temporal mode leads to a Strouhal number of S=0.125 which corresponds to the measured Strouhal number for the vortex shedding (Martinuzzi, 1992). The third and the fourth spatiotemporal modes are connected with the rolls created at the horizontal leading edge of the cube. For the flow field investigated, the dual space-time point of view of POD is rather realistic in the sense that the first four spatiotemporal modes can actually be observed in the flow.

Journal ArticleDOI
TL;DR: In this paper, a finite volume code with a k-e model of turbulence is used to calculate the turbulent flow around and behind triangular-shaped flameholders, and the flow behind the flameholders is found to be unsteady with a well defined Strouhal frequency.
Abstract: Calculations of unsteady turbulent flow around and behind triangular-shaped flameholders using a finite volume code with a k-e model of turbulence are presented. The flow behind the flameholders is found to be unsteady (a von Karman vortex street appears) with a well defined Strouhal frequency (predicted Sr=0·27 compared with an experimental value of 0·25). The predicted profiles of velocity and fluctuating kinetic energy agree well with experiments. The periodic motions in the vortex street are shown to be far more important than the turbulent stochastic motions in exchanging momentum in the transversal direction. The pressure-velocity coupling is handled with the SIMPLEC pressure correction procedure. The discretization in time is fully implicit and 90 times steps are used to resolve one time cycle. It was found that to capture the vortex street it is very important that the grid spacing is sufficiently fine (180 × 100).

Journal ArticleDOI
TL;DR: In this paper, an experimental investigation was carried out on the flow around and the pressure on two tubes (circular cylinders) rigidly mounted in an inline or tandem arrangement using a smoke-wire technique.

Journal ArticleDOI
TL;DR: The far wake of a sphere towed horizontally in a linearly stratified fluid with Froude numbers F ∈ (0.25,12.7) and Reynolds numbers Re ∈ [150,30,000] is investigated in this article.
Abstract: The far wake of a sphere towed horizontally in a linearly stratified fluid with Froude numbers F ∈ (0.25,12.7) and Reynolds numbers Re ∈ [150,30 000] is investigated. Regardless of the initial Froude number, the wake becomes quasi two dimensional at times large compared with the Brunt–Vaisala period. For F≤4.5, the horizontal motions are coherent over the whole depth of the wake. The wake takes the form of a regular von Karman street for F≤1.5 but is irregular at larger F. For F≥4.5 the far wake consists of, vertically incoherent, horizontal motions in several layers. The transition occurs smoothly by a vertical decorrelation of the horizontal motion in the depth of the far which starts at F=4.5. The most novel result is that the horizontal velocity and vertical vorticity diffuse vertically in a time much shorter than predicted by a viscous diffusion law. The ratio of the observed diffusion time to the viscous diffusion time is expected to depend on Reynolds number as is indicated by a simple model.

Journal ArticleDOI
TL;DR: In this article, the authors focus on one versatile set of simple geometries: arrays of circular cylinders in cross flow, by changing cylinder arrangement and the parameters of spacing, damping, and mass ratio, several basic types of self-sustaining oscillations can be produced.
Abstract: There is extreme variety in flow-induced vibrations; they are observed in many diverse situations ranging from reeds in musical instruments to fluttering panels in supersonic airplanes. In order to keep the discussion within bounds, we will focus on one versatile set of simple geometries: arrays of circular cylinders in cross flow. By changing cylinder arrangement and the parameters of spacing, damping, and mass ratio, several different basic types of self-sustaining oscillations can be produced. Because of the industrial importance of tube bundles in heat exchangers, a wealth of observations and analyses has accumulated in the literature (Naudascher & Rockwell 1980). We limit ourselves to discussing cross flow because of the fundamental differences between parallel-flow instabilities and the separated-flow mech­ anisms occurring in cross flow. In parallel flow in or outside of tubes, the cylindrical walls form continuous flow boundaries which curve when there is a vibrational deflection. The dynamic equation for a single tube is a beam equation with "gyroscopic equation" terms added:

Journal ArticleDOI
TL;DR: In this paper, a single panel method was proposed to describe the vortex shedding process in a two-dimensional channel end with infinitely thin, sharp edges by a harmonically varying acoustic flow with zero mean flow.

DissertationDOI
01 Aug 1993
TL;DR: In this article, Towing tank and water channel experiments and a two-dimensional vortex element numerical model were used to study the forces experienced by a flat plate set normal to a nominally 2D flow.
Abstract: : Towing tank and water channel experiments and a two-dimensional vortex element numerical model were used to study the forces experienced by a bluff flat plate set normal to a nominally two-dimensional flow. Intrinsic (small scale) and extrinsic (large scale) three-dimensional motions in the experimental flow were isolated and their separate and combined effects on forces and overall wake development were studied. Transient flow development starting from rest, as well as steady flow conditions, were investigated. A force balance was used to measure the unsteady lift and drag of vertically oriented models projecting through a free surface with various lower end conditions; simultaneous LIF flow visualizations imaged the structure of the vortices in the wake. Plate aspect ratio, lower end condition and angle of attack were varied to effect changes in large scale three-dimensional motions, while changes in Reynolds number and Richardson number (flow stratification) modified the small scale three dimensionality intrinsic to the flow.

Journal ArticleDOI
TL;DR: In this paper, the Strouhal numbers from simulations with zero blockage for Reynolds numbers between 60 and 180 are seen to be in very close agreement with experiments which are said to be effectively two-dimensional.
Abstract: Converged simulations of vortex shedding from a circular cylinder at a Reynolds number of 100 have been computed by the random-vortex method incorporating the influence of blockage. The results are compared with converged finite-element and spectral methods and close agreement for Strouhal number is obtained. Forces are, however, in less close agreement, particularly the fluctuating lift force. Strouhal numbers from simulations with zero blockage for Reynolds numbers between 60 and 180 are seen to be in very close agreement with experiments which are said to be effectively two-dimensional. In this range the Strouhal number changes from 0.135 to 0.191. There are no corresponding experimental measurements for force.

Journal ArticleDOI
TL;DR: In this paper, the authors used laser-induced photochemical anemometry (LIPA) to measure the enstrophy of a Laminar vortex ring approaching a solid planar surface and a free surface.
Abstract: Laminar vortex rings approaching a solid planar surface and a free surface have been investigated experimentally over the range of Reynolds numbers based on the circulation, ReΓ, from 900 to 2350. The emphasis is on the process of vortex stretching, induction of boundary layer on the surface, formation of secondary vortices, and rebounding of the primary vortex ring. Detailed measurements were made using laser‐induced photochemical anemometry (LIPA), a nonintrusive visualization technique which enables multipoint simultaneous measurement of the unsteady velocity field. Results show that enstrophy, rather than circulation, clearly signifies three stages of the behavior of the primary vortex ring—free‐traveling stage, vortex stretching stage, and vortex rebounding stage. Although the flow phenomena are very similar when a vortex ring approaches a solid surface or a slightly contaminated free surface, the difference between the induced boundary layers under two surface conditions is obvious in terms of the circulation and the enstrophy. In addition, the surface deformation and subsequent surface waves resulting from the impacting vortex ring on the contaminated free surface are also discussed. The present study provides a basis for validation and comparison with numerical simulations.