Phenomena of vortex shedding and flow interference of three cylinders in different equilateral arrangements

1988 ◽  
Vol 196 ◽  
pp. 1-26 ◽  
Author(s):  
K. Lam ◽  
W. C. Cheung
Keyword(s):  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Injection Technique ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Visualization Experiments ◽  
Flow Interference ◽  
Bistable Flow

This paper describes how the flows around three equal circular cylinders arranged in an equilateral-triangular manner interact at different angles of incidence α and spacing ratios l/d. Some vortex-shedding-frequency data evaluated from flow visualization experiments conducted at Reynolds numbers of 2.1 × 103 and 3.5 × 103, based on the diameter of a single cylinder, using a dye -injection technique, are presented. In order to provide additional insight to the understanding of the flow structure around this particular cylinder array, some photographs indicating the typical flow patterns for various arrangements are also presented. The investigation indicates that the flows interact in a complex fashion for spacing ratios smaller than 2.29 and it also reveals that, at this range of spacing ratios and at α = 0°, bistable flow characteristic exists. Moreover, for l/d approximately smaller than 4.65 there always exists an angle at which the vortex shedding behind an upstream cylinder is suppressed by a nearest downstream cylinder. This angle is found not to remain constant but increases as the spacing ratio increases. For illustration and comparisons, some numerical results obtained from the application of the surface-vorticity method have also been presented.

A Study on Vortex Shedding From Spheres in a Uniform Flow

1990 ◽  
Vol 112 (4) ◽  
pp. 386-392 ◽  
Author(s):  
H. Sakamoto ◽  
H. Haniu
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Water Channel ◽  
Reynolds Numbers ◽  
Uniform Flow ◽  
Freestream Velocity ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Visualization Experiments

Vortex shedding from spheres at Reynolds numbers from 3 × 102 to 4 × 104 in a uniform flow was investigated experimentally. Standard hot-wire technique were used to measure the vortex shedding frequency from spheres in a low-speed wind tunnel. Flow-visualization experiments were carried out in a water channel. Important results from the investigation were that (i) the variation of the Strouhal number St (=fD/U0, U0: freestream velocity, D: diameter of the sphere, f: vortex shedding frequency) with the Reynolds number (= U0D/v, v: kinematic viscosity) can be classified into four regions, (ii) the Reynolds number at which the hairpinshaped vortices begin to change from laminar to turbulent vortices so that the wake structure behind the sphere is not shown clearly when a Reynolds number of about 800 is reached, and (vi) at Reynolds numbers ranging from 8X102 to 1.5X104, the higher and lower frequency modes of the Strouhal number coexist.

The Effects of Roughness and Shear on Vortex Shedding Cell Lengths Behind a Circular Cylinder

1982 ◽  
Vol 104 (1) ◽  
pp. 72-80 ◽  
Author(s):  
D. M. Rooney ◽  
R. D. Peltzer
Keyword(s):  
Wind Tunnel ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Cell Length ◽  
Circular Cylinders ◽  
Average Cell ◽  
Wide Range ◽  
Shear Parameter ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Circular cylinders of aspect ratio L/D=17 were tested in a wind tunnel under a wide range of spanwise upstream velocity shears. The correlation between upstream shear, characterized by a nondimensional shear parameter β, and the spanwise lengths of constant vortex shedding frequency was sought for both smooth and rough cylinders in transitional Reynolds numbers flows. Among the significant conclusions are that the spanwise range in shedding frequencies decreases with increasing roughness, the average constant shedding frequency cell length increases with increasing roughness for constant shear, and the average cell length decreases with increasing upstream shear for constant roughness.

Investigation of Wall Induced Modifications to Vortex Shedding From a Circular Cylinder

1982 ◽  
Vol 104 (4) ◽  
pp. 518-522 ◽  
Author(s):  
F. Angrilli ◽  
S. Bergamaschi ◽  
V. Cossalter
Keyword(s):  
Velocity Field ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Frequency Measurements ◽  
Geometrical Pattern ◽  
Cylinder Diameter ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

In this paper the influence of a wall on vortex shedding frequency, geometrical pattern, and velocity field are investigated. Frequency measurements were carried out with three circular cylinders at Reynolds numbers of 2860, 3820, and 7640. Mean and fluctuating velocities at several traverses were also measured at Re = 3820 both for an isolated cylinder and for an arrangement with a gap from the wall equal to one cylinder diameter. The modifications of the wake pattern are shown in several figures. It is also shown that the proximity of the wall induces a slight increase of vortex shedding frequency.

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 Visualization of flow past square cylinders with corner modification

2020 ◽  
Vol 4 (3) ◽  
pp. 285-294
Author(s):  
Ch. Krishnappa Vikram ◽  
H. V. Ravindra ◽  
Y. T. Krishnegowda
Keyword(s):  
Aluminum Powder ◽  
Experimental Work ◽  
Vortex Shedding ◽  
Test Section ◽  
Square Cylinder ◽  
Square Cylinders ◽  
Flow Past ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

This article presents the results for flow past a square cylinder and two square cylinders of the same and different sizes with corner modifications by varying the spacing ratio. Here, experimental work is conducted in a recirculatory channel filled with water. A set of aluminum discs made to rotate to create the flow in the test section. The motor is used to vary the speed of the water. Fine aluminum powder is used as a tracer medium. It is observed that vortex shedding frequency decreases by placing the second cylinder in the downstream of the first cylinder. For similar size cylinders, the width of the eddy in the middle of the cylinders increases with an increase in spacing ratio. With the increase of spacing ratio to 6, the flow past each cylinder behaves like a single square cylinder. If the upstream square cylinder size is smaller than the downstream square cylinder, the eddy size is reduced in between the cylinder compared to the downstream of the second cylinder. If the upstream square cylinder size is bigger than the downstream square cylinder, the eddy size is larger in between the cylinder compared to the downstream of the second cylinder.

Unsteady Force Measurements on a Responding Circular Cylinder in the Wake of an Upstream Cylinder

2007 ◽  
Author(s):  
Gustavo R. S. Assi ◽  
Peter W. Bearman ◽  
Julio R. Meneghini
Keyword(s):  
Circular Cylinders ◽  
Force Measurements ◽  
Flow Induced Vibration ◽  
Constant Rate ◽  
Unsteady Force ◽  
Low Mass ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Low Mass Ratio ◽  
Flow Interference

This paper presents force measurements during flow-induced vibration of a pair of circular cylinders with low mass ratio (m* = 2.0) and low damping (ζ = 0.7%) aligned in a tandem arrangement. A particular case with a gap of 3 diameters centre to centre is used to examine flow-interference mechanisms occurring on a downstream cylinder, free to oscillate only in the transverse direction. The Reynolds number varies within the range 1500 < Re < 20000. A cylinder immersed in the wake of another can develop flow-induced oscillations persisting for a large range of reduced velocities. Oscillations are observed for reduced velocities, based on cylinder natural frequency measured in air, as high as 35. Apparently, the amplitude of oscillation is reaching a level of saturation of about 1.5 diameters, while the frequency of vibration is increasing at an approximate constant rate. As reduced velocity is increased two regimes of flow-induced vibration are observed: first vortex-induced vibration and then a wake-induced vibration regime. In addition, the presence of the second cylinder affects the dynamics of the upstream wake, but it is found not to synchronize the vortex shedding frequency of the upstream cylinder for the second regime of oscillations.

An Investigation of the Effects of Incidence on the Flow Around a Square Section Cylinder

1983 ◽  
Vol 34 (4) ◽  
pp. 243-259 ◽  
Author(s):  
E.D. Obasaju
Keyword(s):  
Vortex Shedding ◽  
Pressure Coefficient ◽  
Rate Of Change ◽  
Base Pressure ◽  
Angle Of Incidence ◽  
Spacing Ratio ◽  
Spectral Peaks ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency

SummaryA study has been made of the changes that take place in the flow around a square section cylinder as the angle of incidence is increased from 0° to 45°. Measurements of the Strouhal number, S, and the vortex longitudinal spacing, a/d, are presented and used to estimate the vortex strength,, and vortex street spacing ratio, b/a.is found to vary between about 1.2 and 1.7 depending on incidence, and is given approximately by 0.52(1 - Cpb)/2πS, where Cpbis the mean base pressure coefficient. As the incidence is increased from 0°, S at first decreases slightly and then rises sharply to a maximum at 13.5° incidence, which is the incidence where reattachment of the shear layer, in some mean sense, is expected to commence. The spectra of pressure and velocity fluctuations were measured and subharmonic peaks were found in both spectra at 5° and 10° incidence. It is suggested that they may have been caused by an interaction between a vortex and a trailing edge corner. The degree of organisation of the vortex shedding process was estimated by calculating the sharpness factor, Q, of the spectral peaks at the vortex shedding frequency. In general Q fluctuated with changes in incidence. High values of Q occurred at angles of incidence where the rate of change of the mean base pressure coefficient with incidence is very small whereas low values occurred where the flow is changing to a different state.

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.

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