scholarly journals FLOW AROUND MODIFIED CIRCULAR CILYNDERS

2004 ◽  
Vol 3 (1) ◽  
pp. 62
Author(s):  
R. L. Ferreira ◽  
E. D. R. Vieira
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Vortex Wake ◽  
Continuous Mode ◽  
Longitudinal Slit ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Hot Film ◽  
The Relationship

The flow around a circular cylinder has awaken the attention of different researchers since the historic Strouhal's work of 1878. Ever since, many experimental and numeric works have been carried out in order to determine the relationship between the vortex shedding frequency and the flow regime. Recently, a number of studies have been developed using several small modifications in circular cylinder. In this work a circular cylinder modified with a longitudinal concave notch, has been tested in order to determine the relationship between the non-dimensional vortex shedding frequency (Strouhal number) and the Reynolds number has been determined to Reynolds up to 600. Additionally a modified circular cylinder with a longitudinal slit also has been tested in order to determine the Strouhal-Reynolds relationship in several attack angle configurations. The experiments have been carried out in a vertical low turbulence hydrodynamic tunnel with 146x146x500 mm of test section operating in continuous mode. Flow visualization by direct liquid dye injection has been utilized in order to produce vortex images. These images have been captured in still chemical photography for different Reynolds numbers. A hot-film probe has been adequately positioned in the vortex wake to determine the vortex shedding frequency and consequently the Strouhal number.

scholarly journals FLOW AROUND MODIFIED CIRCULAR CILYNDERS

2004 ◽  
Vol 3 (1) ◽  
Author(s):  
R. L. Ferreira ◽  
E. D. R. Vieira
Keyword(s):  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Continuous Mode ◽  
Longitudinal Slit ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Hot Film ◽  
The Relationship

The flow around a circular cylinder has awaken the attention of different researchers since the historic Strouhal's work of 1878. Ever since, many experimental and numeric works have been carried out in order to determine the relationship between the vortex shedding frequency and the flow regime. Recently, a number of studies have been developed using several small modifications in circular cylinder. In this work a circular cylinder modified with a longitudinal concave notch, has been tested in order to determine the relationship between the non-dimensional vortex shedding frequency (Strouhal number) and the Reynolds number has been determined to Reynolds up to 600. Additionally a modified circular cylinder with a longitudinal slit also has been tested in order to determine the Strouhal-Reynolds relationship in several attack angle configurations. The experiments have been carried out in a vertical low turbulence hydrodynamic tunnel with 146x146x500 mm of test section operating in continuous mode. Flow visualization by direct liquid dye injection has been utilized in order to produce vortex images. These images have been captured in still chemical photography for different Reynolds numbers. A hot-film probe has been adequately positioned in the vortex wake to determine the vortex shedding frequency and consequently the Strouhal number.

Studying Three-Dimensionality of Vortex Shedding Behind a Circular Cylinder with Mems Sensors

2007 ◽  
Vol 23 (2) ◽  
pp. 107-116 ◽  
Author(s):  
J. K. Tu ◽  
J. J. Miau ◽  
Y. J. Wang ◽  
G. B. Lee ◽  
C. Lin
Keyword(s):  
Aspect Ratio ◽  
Circular Cylinder ◽  
Wavelet Analysis ◽  
Vortex Shedding ◽  
Reynolds Numbers ◽  
Splitter Plate ◽  
Mems Sensors ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

AbstractExperiments were made with 14 MEMS sensors situated along the span of a circular cylinder whose aspect ratio was 5. The signals of the MEMS sensors were sampled simultaneously as flow over the cylinder at Reynolds numbers of 104. The results of Wavelet analysis of the signals indicate that the percentage of time during which strong three-dimensionality of vortex shedding was detected is about 10%.As noted, strong three-dimensionality took place when the fluctuating amplitude of the signals was severely modulated and the vortex shedding frequency reduced appeared abnormally high or low. Further noted was that the addition of a splitter plate of 0.5 or one diameter in length behind the circular cylinder was not able to suppress the three-dimensionality of the flow.

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.

Vortex-Induced Vibration Characteristics of an Elastic Square Cylinder on Fixed Supports

2004 ◽  
Vol 127 (2) ◽  
pp. 241-249 ◽  
Author(s):  
Z. J. Wang ◽  
Y. Zhou
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Flow Separation ◽  
Natural Frequencies ◽  
Separation Point ◽  
Square Cylinder ◽  
Vortex Induced Vibration ◽  
The Third ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The vortex-induced structural vibration of an elastic square cylinder, on fixed supports at both ends, in a uniform cross flow was measured using fiber-optic Bragg grating sensors. The measurements are compared to those obtained for an elastic circular cylinder of the same hydraulic diameter in an effort to understand the effect of the nature (fixed or oscillating) of the flow separation point on the vortex-induced vibration. It is found that a violent vibration occurs at the third-mode resonance when the vortex-shedding frequency coincides with the third-mode natural frequency of the fluid-structure system, irrespective of the cross-sectional geometry of the cylinder. This is in distinct contrast to previous reports of flexibly supported rigid cylinders, where the first-mode vibration dominates, thus giving little information on the vibration of other modes. The resonance behavior is neither affected by the incidence angle (α) of the free stream, nor by the nature of the flow separation point. However, the vibration amplitude of the square cylinder is about twice that of the circular cylinder even though the flexural rigidity of the former is larger. This is ascribed to a difference in the nature of the flow separation point between the two types of structures. The characteristics of the effective modal damping ratios, defined as the sum of structural and fluid damping ratios, and the system natural frequencies are also investigated. The damping ratios and the system natural frequencies vary little with the reduced velocity at α=0deg, but appreciable at α⩾15deg; they further experience a sharp variation, dictated by the vortex-shedding frequency, near resonance.

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.

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.

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.

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