Vortex Shedding in a Tandem Circular Cylinder System With a Yawed Downstream Cylinder

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Stephen J. Wilkins ◽  
James D. Hogan ◽  
Joseph W. Hall
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Large Body ◽  
Flow Regimes ◽  
Small Scale ◽  
Mean Flow ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Local Spacing

This investigation examines the flow produced by a tandem cylinder system with the downstream cylinder yawed to the mean flow direction. The yaw angle was varied from α=90deg (two parallel tandem cylinders) to α=60deg; this has the effect of varying the local spacing ratio between the cylinders. Fluctuating pressure and hot-wire measurements were used to determine the vortex-shedding frequencies and flow regimes produced by this previously uninvestigated flow. The results showed that the frequency and magnitude of the vortex shedding varies along the cylinder span depending on the local spacing ratio between the cylinders. In all cases the vortex-shedding frequency observed on the front cylinder had the same shedding frequency as the rear cylinder. In general, at small local spacing ratios the cylinders behaved as a single large body with the shear layers separating from the upstream cylinder and attaching on the downstream cylinder, this caused a correspondingly large, low frequency wake. At other positions where the local span of the tandem cylinder system was larger, small-scale vortices began to form in the gap between the cylinders, which in turn increased the vortex-shedding frequency. At the largest spacings, classical vortex shedding persisted in the gap formed between the cylinders, and both cylinders shed vortices as separate bodies with shedding frequencies typical of single cylinders. At certain local spacing ratios two distinct vortex-shedding frequencies occurred indicating that there was some overlap in these flow regimes.

Vortex Shedding in a Yawed-Tandem Circular Cylinder Arrangement

2010 ◽  
Author(s):  
Stephen J. Wilkins ◽  
James D. Hogan ◽  
Joseph W. Hall
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Large Body ◽  
Flow Regimes ◽  
Small Scale ◽  
Mean Flow ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Local Spacing

This investigation examines the flow produced by a tandem cylinder system with the downstream cylinder yawed to the mean flow direction. The yaw angle was varied from α = 90° (two parallel tandem cylinders) to α = 60°; this has the effect of varying the local spacing ratio between the cylinders. Fluctuating pressure and hot-wire measurements were used to determine the vortex-shedding frequencies and flow regimes produced by this previously uninvestigated flow. The results showed that the frequency and magnitude of the vortex-shedding varies along the cylinder span depending on the local spacing ratio between the cylinders. In all cases the vortex-shedding frequency observed on the front cylinder had the same shedding frequency as the rear cylinder. In general, at small local spacing ratios the cylinders behaved as a single large body with the shear layers separating from the upstream cylinder and attaching on the downstream cylinder, this caused a correspondingly large, low frequency wake. At other positions where the local span of the tandem cylinder system was larger, small scale vortices began to form in the gap between the cylinders which in turn increased the vortex-shedding frequency. At the largest spacings, classical vortex-shedding persisted in the gap formed between the cylinders and both cylinders shed vortices as separate bodies with shedding frequencies typical of single cylinders. At certain local spacing ratios two distinct vortex-shedding frequencies occurred indicating that there was some overlap in these flow regimes.

The Spanwise Dependence of Vortex-Shedding From Yawed Circular Cylinders

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
James D. Hogan ◽  
Joseph W. Hall
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Rapid Decrease ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Independence Principle ◽  
Simultaneous Measurements ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency

Simultaneous measurements of the fluctuating wall pressure along the cylinder span were used to examine the spanwise characteristics of the vortex-shedding for yaw angles varying from α=60 deg to α=90 deg. The Reynolds number based on the diameter of the cylinder was 56,100. The results indicate that yawing the cylinder to the mean flow direction causes the vortex-shedding in the wake to become more disorderly. This disorder is initiated at the upstream end of the cylinder and results in a rapid decrease in correlation length, from 3.3D for α=90 deg to 1.1D for α=60 deg. The commonly used independence principle was shown to predict the vortex-shedding frequency reasonably well along the entire cylinder span for α>70 deg, but did not work as well for α=60 deg.

The Spanwise Dependence of Vortex-Shedding From Yawed Circular Cylinders

2009 ◽  
Author(s):  
James D. Hogan ◽  
Joseph W. Hall
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Rapid Decrease ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Independence Principle ◽  
Simultaneous Measurements ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency

Simultaneous measurements of the fluctuating wall pressure along the cylinder span were used to examine the spanwise characteristics of the vortex-shedding for yaw angles varying from α = 60° to α = 90°. The Reynolds number based upon the diameter of the cylinder was 56,100. The results indicate that yawing the cylinder to the mean flow direction causes the vortex-shedding in the wake to become more disorderly. This disorder is initiated at the upstream end of the cylinder and results in a rapid decrease in correlation length, from 3.3D for α = 90° to 1.1D for α = 60°. The commonly used independence principle was shown to predict the vortex-shedding frequency reasonably well along the entire cylinder span for α > 70°, but did not work as well for α = 60°.

Influence of slip on the flow past superhydrophobic circular cylinders

2011 ◽  
Vol 680 ◽  
pp. 459-476 ◽  
Author(s):  
PRANESH MURALIDHAR ◽  
NANGELIE FERRER ◽  
ROBERT DANIELLO ◽  
JONATHAN P. ROTHSTEIN
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Superhydrophobic Surfaces ◽  
Separation Point ◽  
Circular Cylinders ◽  
Recirculation Region ◽  
Small Scale ◽  
Flow Past ◽  
Shedding Frequency

Superhydrophobic surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large- and small-scale channels. In this paper, a series of experiments were performed which investigated the effect of superhydrophobic-induced slip on the flow past a circular cylinder. In these experiments, circular cylinders were coated with a series of superhydrophobic surfaces fabricated from polydimethylsiloxane with well-defined micron-sized patterns of surface roughness. The presence of the superhydrophobic surface was found to have a significant effect on the vortex shedding dynamics in the wake of the circular cylinder. When compared to a smooth, no-slip cylinder, cylinders coated with superhydrophobic surfaces were found to delay the onset of vortex shedding and increase the length of the recirculation region in the wake of the cylinder. For superhydrophobic surfaces with ridges aligned in the flow direction, the separation point was found to move further upstream towards the front stagnation point of the cylinder and the vortex shedding frequency was found to increase. For superhydrophobic surfaces with ridges running normal to the flow direction, the separation point and shedding frequency trends were reversed. Thus, in this paper we demonstrate that vortex shedding dynamics is very sensitive to changes of feature spacing, size and orientation along superhydrophobic surfaces.

Stability properties of forced wakes

2007 ◽  
Vol 579 ◽  
pp. 137-161 ◽  
Author(s):  
B. THIRIA ◽  
J. E. WESFREID
Keyword(s):  
Vortex Shedding ◽  
Mean Flow ◽  
Near Wake ◽  
Global Mode ◽  
Spatial Properties ◽  
Moderate Reynolds Number ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
The Stability ◽  
Selection Of

Thiria, Goujon-Durand & Wesfreid (J. Fluid Mech. vol. 560, 2006, p. 123), it was shown that vortex shedding from a rotationally oscillating cylinder at moderate Reynolds number can be characterized by the spatial coexistence of two distinct patterns, one of which is related to the forcing frequency in the near wake and the other to a frequency close to the natural one for the unforced case downstream of this locked region. The existence and the modification of these wake characteristics were found to be strongly affected by the frequency and the amplitude of the cylinder oscillation. In this paper, a linear stability analysis of these forced regimes is performed, and shows that the stability characteristics of such flows are governed by a strong mean flow correction which is a function of the oscillation parameters. We also present experiments on the spatial properties of the global mode and on the selection of the vortex shedding frequency as a function of the forcing conditions for Re = 150. Finally, we elucidate a diagram of locked and non-locked states, for a large range of frequencies and amplitudes of the oscillation.

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.

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.

In-Situ Measurement of Thermowell Vibration During Production Train Pressurization

2002 ◽  
Author(s):  
Paul N. Finch ◽  
Michael G. Hamblin ◽  
Damien C. Constable
Keyword(s):  
Vortex Shedding ◽  
Flow Direction ◽  
Vibration Measurement ◽  
Start Up ◽  
Form Part ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Mechanism Of Failure ◽  
Flow Velocities

Fatigue failure of intrusive fittings such as erosion probes, sample quills and thermowells, has occurred in Woodside’s offshore and onshore operations. The mechanism of failure is generally thought to be resonant vibration caused by vortex shedding. The consequence of these failures can be severe, in particular for thermowells, as they form part of the pressure envelope, and hydrocarbon release can result. Thermowells on the Goodwyn Alpha platform flow lines were designed to withstand the maximum normal operating flow velocities. During production train pressurisation, however, the thermowells can experience velocities higher than the design limit, albeit for a limited time. These start up flow velocities are likely to cause vortex shedding frequencies exceeding flowline thermowell resonant frequencies. If a vortex shedding frequency occurs that is close to a thermowell natural frequency, a vortex “lock on” resonance can occur, resulting in large amplitude thermowell vibration transverse to the flow direction. In order to determine if thermowell replacement was warranted, a study was undertaken to measure the thermowells in situ. The specific aims were: to determine if vortex “lock on” was occurring; and to determine what cyclic stresses are present. To do this, a novel vibration measurement probe was developed and commissioned. The probe is capable of measuring bidirectional acceleration in thermowells without the need for the thermowell to be taken offline. This paper presents the development of the probe and the results of the measurements during flowline pressurisation.

The Unsteady Lift on Bluff Cylindrical Bodies in Unsteady Flow

1982 ◽  
Vol 33 (3) ◽  
pp. 219-236 ◽  
Author(s):  
H. Stapountzis ◽  
J.M.R. Graham
Keyword(s):  
Vortex Shedding ◽  
Elliptic Cylinder ◽  
Reynolds Numbers ◽  
Bluff Bodies ◽  
Mean Flow ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency ◽  
Naca 0015 ◽  
Unsteady Lift

SummaryThe unsteady lift generated on a NACA 0015 aerofoil, a D cylinder (with the flat face down-stream) and an elliptic cylinder was measured when these bodies were exposed to a flow with a two-dimensional sinusoidal upwash at reduced frequencies 0.05 to 0.8. The mean flow Reynolds numbers were in the range 1.2 × 105 to 3 × 105. Unsteady thin aerofoil theory was used in an attempt to predict the unsteady lift on the bluff bodies, as well as the aerofoil section for fequencies in the low range below the vortex shedding frequency. The results were quite accurate for the aerofoil and the D cylinder, but the aerodynamic admittance predicted by this theory for the elliptic cylinder was significantly above that measured experimentally. The movement of the two free separation points was found to play an important role in the characteristic lift behaviour of the elliptic cylinder.

scholarly journals Investigation of passive control of the wake past a thick plate by stability and sensitivity analysis of experimental data

2017 ◽  
Vol 828 ◽  
pp. 753-778 ◽  
Author(s):  
S. Camarri ◽  
R. Trip ◽  
J. H. M. Fransson
Keyword(s):  
Experimental Data ◽  
Sensitivity Analysis ◽  
Vortex Shedding ◽  
Flow Model ◽  
Flow Fields ◽  
Mean Flow ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency ◽  
The Stability

In this paper we propose a strategy, entirely relying on available experimental data, to estimate the effect of a small control rod on the frequency of vortex shedding in the wake past a thick perforated plate. The considered values of the flow Reynolds number range between $Re\simeq 6.6\times 10^{3}$ and $Re=5.3\times 10^{4}$. By means of particle image velocimetry, an experimental database consisting of instantaneous flow fields is collected for different values of suction through the body surface. The strategy proposed here is based on classical stability and sensitivity analysis applied to mean flow fields and on the formulation of an original ad hoc model for the mean flow. The mean flow model is obtained by calibrating the closure of the Reynolds averaged Navier–Stokes equations on the basis of the available experimental data through an optimisation algorithm. As a result, it is shown that the predicted control map agrees reasonably well with the equivalent one measured experimentally. Moreover, it is shown that even when turbulence effects are neglected, the stability analysis applied to the mean flow fields provides a reasonable estimation of the vortex shedding frequency, confirming what is known in the literature and extending it up to $Re=5.3\times 10^{4}$. It is also shown that, when turbulence is taken into account in the stability analysis using the same closure that is calibrated for the corresponding mean flow model, the prediction of the vortex shedding frequency is systematically improved.

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