A Study of Vortex Shedding in a Staggered Tube Array for Steady and Pulsating Cross-Flow

2002 ◽  
Vol 124 (3) ◽  
pp. 737-746 ◽  
Author(s):  
E. Konstantinidis ◽  
S. Balabani ◽  
M. Yianneskis
Keyword(s):  
Experimental Investigation ◽  
Steady Flow ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Frequency Component ◽  
Flow Patterns ◽  
Visualization Technique ◽  
Velocity Fluctuations ◽  
Flow Fluctuations ◽  
Shedding Frequency

This paper describes an experimental investigation of the vortex shedding phenomena in a staggered tube array with streamwise and transverse spacing to diameter ratios of 2.1 and 3.6, respectively. LDA measurements were employed to monitor the flow fluctuations and a visualization technique was implemented to reveal the underlying flow patterns in the array for steady and pulsating cross-flow. The results obtained in steady flow are in general agreement with results from previous investigations and show that vortex shedding occurs at two distinct frequencies in the front and inner rows. A lower frequency component was detected at the exit of the array, which has not been previously identified. Pulsating flow caused the frequency of vortex shedding to lock-on at the subharmonic of the imposed frequency. In the lock-on range, vortex shedding from all the tubes was synchronized and in-phase and velocity fluctuations at the shedding frequency increased considerably compared to their counterparts in steady flow.

Incoherent turbulence structure in the near wake of a normal plate

1988 ◽  
Vol 190 ◽  
pp. 343-356 ◽  
Author(s):  
M. Kiya ◽  
M. Matsumura
Keyword(s):  
Vortex Shedding ◽  
Frequency Component ◽  
Turbulence Structure ◽  
Near Wake ◽  
Velocity Fluctuations ◽  
Coherent Vortices ◽  
Frequency Components ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Small Dispersion

In this paper experimentally studied characteristics of various frequency components of incoherent velocity fluctuations in the near wake behind a thin normal plate immersed in a uniform flow are described. Measurements were made at a position 8 plate heights downstream of the plate where the wake had a marked periodicity, so that coherent vortices shed from the plate are expected to have a small dispersion in streamwise spacing, transverse location, strength and shape. Shearing stress associated with the incoherent fluctuations is mainly contributed by components with frequencies around half of the vortex-shedding frequency fs on one side of the wake. The ½fs frequency component appears to be caused by the spanwise locations of ribs, which are connected to the coherent vortices, being different from vortex to vortex. A probable spanwise arrangement of the ribs is suggested.

Effect of Tube Spacing on the Vortex Shedding Characteristics of Laminar Flow Past an Inline Tube Array

2008 ◽  
Author(s):  
C. Liang ◽  
X. Luo ◽  
G. Papadakis
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Unstructured Grid ◽  
Flow Patterns ◽  
Instantaneous Flow ◽  
Flow Past ◽  
Recirculation Zones ◽  
Shedding Frequency ◽  
Drag And Lift ◽  
Lift And Drag

The effect of tube spacing on the vortex shedding characteristics and fluctuating forces in an inline tube array is examined. The array consists of 6 cylinders in tandem, the examined Reynolds number is 100 and the flow is laminar. The numerical methodology and the code employed to solve the equations in an unstructured grid are validated against available results from the literature for the flow past two cylinders in tandem. Computations are then performed for the 6 row inline bank for 8 pitch-to-diameter ratios s ranging from 2.1 to 4. The instantaneous flow patterns are visualised for different spacings and the lift and drag coefficients for all cylinders are recorded and analysed. At the smallest spacing examined (s = 2.1) there are five stagnant and symmetric recirculation zones and weak vortex shedding activity occurs behind the last cylinder only. As s increases, the symmetry of the recirculation zones breaks leading to vortex shedding. This process progressively moves upstream, so that for s = 4 there is clear shedding for every row. The shedding frequency behind each cylinder is the same and increases with tube spacing. A spacing region between 3d and 3.6d is identified, within which rms drag and lift coefficients attain maximum values. This behaviour is explained with the aid of instantaneous flow patterns.

A contribution to an inviscid vortex-shedding model for an inclined flat plate in uniform flow

1977 ◽  
Vol 82 (2) ◽  
pp. 223-240 ◽  
Author(s):  
Masaru Kiya ◽  
Mikio Arie
Keyword(s):  
Flat Plate ◽  
Vortex Shedding ◽  
Separated Flow ◽  
Flow Patterns ◽  
Shear Layers ◽  
Visualization Technique ◽  
Time Intervals ◽  
Discrete Vortex ◽  
Kutta Condition ◽  
Vorticity Transport

Unsteady separated flow behind an inclined flat plate is numerically studied through the use of the discrete-vortex approximation, in which the shear layers emanating from the edges of the plate are represented by an array of discrete vortices introduced into the flow field at appropriate time intervals at some fixed points near the edges of the plate. The strengths of the nascent vortices are chosen so as to satisfy the Kutta condition at the edges of the plate. Numerical calculations are performed for a plate at 60° incidence impulsively started from rest in an otherwise stationary incompressible fluid, by systematically changing the distance between the location of the nascent vortices and the edges of the plate. The temporal changes in the drag force, the rate of vorticity transport at both edges of the plate and the velocity of the separated shear layers are given together with the flow patterns behind the plate on the basis of this model. The results of the computation show that the vortex street behind the plate inclines as a whole towards the direction of the time-averaged lift force exerted on the plate. It is also predicted from the calculations that the vortex shedding at one edge of the plate will not occur at the mid-interval of the successive vortex shedding at the other edge. The predicted flow patterns are not inconsistent with a few experimental observations based on the flow-visualization technique.

Computational Determination of the Modified Vortex Shedding Frequency for a Rigid, Truncated, Wall-Mounted Cylinder in Cross Flow

2014 ◽  
Author(s):  
Aimie Faucett ◽  
Todd Harman ◽  
Tim Ameel
Keyword(s):  
Vortex Shedding ◽  
Cross Flow ◽  
Classical Case ◽  
Reynolds Numbers ◽  
Two Dimensional ◽  
End Effects ◽  
Dimensional Solution ◽  
Horseshoe Vortices ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Flow around a rigid, truncated, wall-mounted cylinder with an aspect ratio of 5 is examined computationally at various Reynolds numbers Re to determine how the end effects impact the vortex shedding frequency. The existence of the wall and free end cause a dampening of the classical shedding frequency found for a semi-infinite, two-dimensional cylinder, as horseshoe vortices along the wall and flow over the tip entrain into the shedding region. This effect was observed for Reynolds numbers in the range of 50 to 2000, and quantified by comparing the modified Strouhal numbers to the classical (two-dimensional) solution for Strouhal number as a function of Reynolds number. The range of transition was found to be 220 < Re < 300, versus 150 < Re < 300 for the classical case. Vortex shedding started at Re ≈ 100, significantly above Re = 50, where shedding starts for the two-dimensional case.

Vortex shedding from a cylinder vibrating in line with an incident uniform flow

1976 ◽  
Vol 75 (2) ◽  
pp. 257-271 ◽  
Author(s):  
Owen M. Griffin ◽  
Steven E. Ramberg
Keyword(s):  
Vortex Shedding ◽  
Vibration Amplitude ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Vortex Wake ◽  
Single Vortex ◽  
Vortex Pairs ◽  
Wake Patterns ◽  
Shedding Frequency ◽  
Basic Characteristics

A study has been made of the wake of a cylinder vibrating in line with an incident steady flow. The Reynolds number for the experiments was 190, and the vortex shedding was at all times synchronized with the vibrations of the cylinder, which were in a range of frequencies near twice the Strouhal shedding frequency for the stationary cylinder. Two distinct vortex wake patterns were encountered. The first is a complex regime in which two vortices are shed during each cycle of the vibration and form an alternating pattern of vortex pairs downstream. The second pattern is an alternating street which results from the shedding of a single vortex during each cycle of the cylinder's motion. The street geometry in the latter case shares many basic characteristics with the wake of a cylinder vibrating in cross-flow. These include the effects of vibration amplitude and frequency on the longitudinal and transverse spacing of the vortices. The results obtained from these experiments in air are in agreement with previous findings from free- and forced-vibration experiments in water at both higher and lower Reynolds numbers.

Elastically Mounted Body in Cross Flow With an Attached Pendulum

1993 ◽  
Author(s):  
Aleš Tondl
Keyword(s):  
Vortex Shedding ◽  
Parametric Excitation ◽  
Trivial Solution ◽  
Cross Flow ◽  
Vertical Vibration ◽  
The Body ◽  
Autoparametric Resonance ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
The Stability

Abstract A pendulum is attached to an elastically mounted body in cross flow. The body is excited due to the action of vortex shedding. The stability of the semi-trivial solution (representing the vibration of the body with the non-oscillating pendulum) is investigated. It is proved that a certain interval of the vortex shedding frequency can exist where the semi-trivial solution representing the vertical vibration of the body is unstable. The body vibration is the source of parametric excitation of the pendulum resulting in autoparametric resonance.

An experimental study of steady and pulsating cross-flow over a semi-staggered tube bundle

2005 ◽  
Vol 219 (3) ◽  
pp. 283-298 ◽  
Author(s):  
E Konstantinidis ◽  
D Castiglia ◽  
S Balabani
Keyword(s):  
Experimental Study ◽  
Vortex Shedding ◽  
Considerable Increase ◽  
Tube Bundle ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Velocity Fields ◽  
Velocity Fluctuations ◽  
The Mean

This paper describes an experimental study of the cross-flow characteristics in a semi-staggered tube bundle for Reynolds numbers in the range 1100-12 900. It is shown that by displacing transversely the tubes in the even rows of an in-line bundle by one diameter the vortex-shedding mechanism is suppressed. Vortex shedding is re-established and reinforced by pulsations superimposed on to the approaching flow and a considerable increase in the power of the associated velocity fluctuations is observed in the bundle. Two cases of pulsating flow are examined with different effects on the flow structure of the bundle. Detailed measurements of the mean and fluctuating velocity fields in the semi-staggered tube bundle together with flow visualization images are also reported in the paper in order to examine in depth the effects of tube displacement and flow pulsations. Comparisons with in-line and staggered configurations having the same spacing-to-diameter ratios are made.

Free vibrations of two side-by-side cylinders in a cross-flow

2001 ◽  
Vol 443 ◽  
pp. 197-229 ◽  
Author(s):  
Y. ZHOU ◽  
Z. J. WANG ◽  
R. M. C. SO ◽  
S. J. XU ◽  
W. JIN
Keyword(s):  
Vortex Shedding ◽  
Natural Frequencies ◽  
Cross Flow ◽  
Free Vibrations ◽  
Dynamic Strain ◽  
Valuable Insight ◽  
Combined System ◽  
Sharp Variation ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Free vibrations of two side-by-side cylinders with fixed support (no rotation and displacement) at both ends placed in a cross-flow were experimentally investigated. Two fibre-optic Bragg grating sensors were used to measure the dynamic strain, while a hot wire and flow visualization were employed to examine the flow field around the cylinders. Three T/d ratios, 3.00, 1.70 and 1.13, were investigated, where T is the centre-to-centre cylinder spacing and d is the diameter; they give rise to three different flow regimes. The investigation throws new light on the shed vortices and their evolution. A new interpretation is proposed for the two different dominant frequencies, which are associated with the narrow and the wide wake when the gap between the cylinders is between 1.5 and 2.0 as reported in the literature. The structural vibration behaviour is closely linked to the flow characteristics. At T/d = 3:00, the cross-flow root-mean-square strain distribution shows a very prominent peak at the reduced velocity Ur ≈ 26 when the vortex shedding frequency fs, coincides with the third-mode natural frequency of the combined fluid–cylinder system. When T/d < 3:00, this peak is not evident and the vibration is suppressed because of the weakening strength of the vortices. The characteristics of the system modal damping ratios, including both structural and fluid damping, and natural frequencies are also investigated. It is found that both parameters depend on T/d. Furthermore, they vary slowly with Ur, except near resonance where a sharp variation occurs. The sharp variation in the natural frequencies of the combined system is dictated by the vortex shedding frequency, in contrast with the lock-in phenomenon, where the forced vibration of a structure modifies the vortex shedding frequency. This behaviour of the system natural frequencies persists even in the case of the single cylinder and does not seem to depend on the interference between cylinders. A linear analysis of an isolated cylinder in a cross-flow has been carried out. The linear model prediction is qualitatively consistent with the experimental observation of the system damping ratios and natural frequencies, thus providing valuable insight into the physics of fluid–structure interactions.

Numerical simulations of steady flow past two cylinders in staggered arrangements

2015 ◽  
Vol 765 ◽  
pp. 114-149 ◽  
Author(s):  
Feifei Tong ◽  
Liang Cheng ◽  
Ming Zhao
Keyword(s):  
Steady Flow ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Velocity Signal ◽  
Flow Features ◽  
Flow Information ◽  
Lift Forces ◽  
Pitch Distance

AbstractThis paper presents a numerical study on steady flow around two identical circular cylinders of various arrangements at a low subcritical Reynolds number ($\mathit{Re}=10^{3}$). The ratio of centre-to-centre pitch distance ($P$) to the diameter of the cylinder ($D$) ranges from 1.5 to 4, and the alignment angle $({\it\alpha})$ between the two cylinders and the direction of the cross-flow varies from 0 to 90°. The detailed flow information obtained from direct numerical simulation allows a comprehensive interpretation of the underlying physics responsible for some interesting flow features observed around two staggered cylinders. Four distinct vortex shedding regimes are identified and it is demonstrated that accurate classification of vortex shedding regimes around two staggered cylinders should consider the combination of the flow visualization with the analyses of lift forces and velocity signal in the wake. It is revealed that the change in pressure distribution, as a result of different vortex shedding mechanisms, leads to a variety of characteristics of hydrodynamic forces on both cylinders, including negative drag force, attractive and repulsive lift forces. Two distinct vortex shedding frequencies are identified and are attributed to the space differences based on the flow structures observed in the wake of the cylinders. It is also found that the three-dimensionality of flow in the gap and the shared wake region is significantly weakened in almost two of the classified flow regimes; however, compared with the flow around a single cylinder, active wake interaction at large ${\it\alpha}$ does not clearly increase the three-dimensionality.

An Experimental Investigation Into the Breakdown of Low Reynolds Number Pulsed Flows at a Pipe Orifice

1997 ◽  
Vol 119 (2) ◽  
pp. 347-353 ◽  
Author(s):  
P. S. Addison ◽  
D. A. Ervine ◽  
A. H. C. Chan ◽  
K. J. Williams
Keyword(s):  
Experimental Investigation ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Control Parameters ◽  
Experimental Apparatus ◽  
Pulsed Flows ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Growth Evolution ◽  
Downstream Development

An experimental investigation into the behavior of pulsed vortex flows in water at a pipe orifice is outlined. An experimental apparatus is described whereby flow pulsations are generated using an electronically controlled motor-piston arrangement. Preliminary investigations are made into the unpulsed system to determine the natural vortex shedding frequency for various Reynolds numbers and orifice diameters. The downstream development of initially axisymmetric, periodically pulsed vortices shed from the orifice plate are then examined. The growth, evolution, and eventual breakdown of the initially axisymmetric vortices are investigated for a range of flow control parameters. Various flow regimes are discerned and an attempt is made to categorize them.

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