A Numerical Study of Vortex Shedding From One and Two Circular Cylinders

1981 ◽  
Vol 32 (1) ◽  
pp. 48-71 ◽  
Author(s):  
P.K. Stansby
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Potential Flow ◽  
Numerical Study ◽  
Circular Cylinders ◽  
Discrete Vortex ◽  
Formation Region ◽  
Flow Features ◽  
The Mean

SummaryA discrete-vortex representation of the wake of a circular cylinder, in which vortices are convected in a potential-flow calculation and maintain their identities unless they approach one another or a surface closely, predicts many of the unsteady flow features and is computationally more efficient than other schemes. The mean rate of shedding of vorticity is adjusted to be compatible with experiments at a high subcritical Reynolds number of 3 × 104 and the model gives reasonable predictions of separation, drag, lift, Strouhal number and vorticity loss in the formation region. The method is extended to accommodate a second cylinder and many of the surprising features which have been observed experimentally with two cylinders in a side-by-side arrangement are reproduced.

A Numerical Study of Geometrical Effects on the Strouhal Number of a Circular Cylinder

2008 ◽  
Author(s):  
Farzan Kazemifar ◽  
Mehdi Molai ◽  
Bahar Firoozabadi ◽  
Goodarz Ahmadi
Keyword(s):  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Circular Cylinders ◽  
Percentage Reduction ◽  
Blade Angle ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Geometrical Effects

In this paper, reducing the Strouhal number of a circular cylinder is studied numerically. Two-dimensional numerical simulations of flow over a normal circular cylinder and various modified circular cylinders are carried out using FLUENT® soft ware. Two small blades are attached to a circular cylinder and the effects of variation of the blades length and the blade angle are studied numerically. The blade angle is chosen 2α = 0°, 30°, 90°, 120° and 150°. The blades length is chosen l/d = 0.125, 0.25, 0.375. Effects of blade angles and blade lengths were studied for both 2α = 0° and 150°. Results show that increasing in blade lengths decreases the Strouhal number. Moreover, as the blade angle was increased from zero to 90°, the percentage reduction in Strouhal number decreased; however, as the blade angle was further increased from 90° to 150°, the percentage reduction in Strouhal number increased. Although the modifications studied here decrease the vortex shedding frequency they make the vortices shed from the cylinder farther and stronger hence increasing the magnitude of the fluctuating forces.

A Numerical Investigation of the Effects of Flow Pulsations on the Drag Force Over a Cylinder

2011 ◽  
Author(s):  
Eric D’herde ◽  
Laila Guessous
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Free Stream ◽  
Stream Velocity ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency

Flow over a cylinder is a fundamental fluid mechanics problem that involves a simple geometry, yet increasingly complex flow patterns as the Reynolds number is increased, most notably the development of a Karman vortex with a natural vortex shedding frequency fs when the Reynolds number exceeds a value of about 40. The goal of this ongoing study is to numerically investigate the effect of an incoming free-stream velocity pulsation with a mean Reynolds number of 100 on the drag force over and vorticity dynamics behind a circular cylinder. This paper reports on initial results involving unsteady, laminar and incompressible flows over a circular cylinder. Sinusoidal free-stream pulsations with amplitudes Av varying between 25% and 75% of the mean free-stream velocity and frequencies f varying between 0.25 and 5 times the natural shedding frequency were considered. Of particular interest to us is the interaction between the pulsating frequency and natural vortex shedding frequency and the resulting effects on drag. Interestingly, at frequencies close to the natural frequency, and to twice the natural frequency, a sudden drop in the mean value of the drag coefficient is observed. This drop in the drag coefficient is also accompanied by a change in the flow and vortex shedding patterns observed behind the cylinder.

A Numerical Investigation of the Effects of Flow Pulsations on the Vortex Shedding, Drag and Lift Forces Over a Cylinder

2011 ◽  
Author(s):  
Eric D’herde ◽  
Laila Guessous
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Free Stream ◽  
Lift Coefficient ◽  
Stream Velocity ◽  
Vortex Shedding Frequency ◽  
The Mean ◽  
Shedding Frequency ◽  
Drag And Lift

Flow over a cylinder is a fundamental fluid mechanics problem that involves a simple geometry, yet increasingly complex flow patterns as the Reynolds number is increased, most notably the development of a Karman vortex with a natural vortex shedding frequency when the Reynolds number exceeds a value of about 40. The goal of this ongoing study is to numerically investigate the effect of an incoming free-stream velocity pulsation with a mean Reynolds number of 100 on the drag and lift forces over and vorticity dynamics behind a circular cylinder. This paper reports on initial results involving unsteady, laminar and incompressible flows over a circular cylinder. Sinusoidal free-stream pulsations with amplitudes Av varying between 25% and 75% of the mean free-stream velocity and frequencies varying between 0.25 and 5 times the natural shedding frequency fs were considered. Of particular interest to us is the interaction between the pulsating frequency and natural vortex shedding frequency and the resulting effects on drag. Interestingly, at frequencies close to the natural frequency, and to twice the natural frequency, a sudden drop in the mean value of the drag coefficient is observed. The first drop in the drag coefficient, i.e. near f = fs, is also accompanied by a change in the flow and vortex shedding patterns observed behind the cylinder. This change in vortex shedding pattern manifests itself as a departure from symmetrical shedding, and in a non-zero mean lift coefficient value. The second drop, i.e. near f = 2 fs, has similar characteristics, except that the mean lift coefficient remains at zero.

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.

Appraisal of Universal Wake Numbers From Data for Roughened Circular Cylinders

1983 ◽  
Vol 105 (4) ◽  
pp. 464-468 ◽  
Author(s):  
G. Buresti
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Vortex Shedding ◽  
Physical Interpretation ◽  
Potential Flow ◽  
Bluff Body ◽  
Cross Flow ◽  
Sufficient Accuracy ◽  
Circular Cylinders

An analysis was carried out to check whether certain existing universal wake numbers can characterize the cross-flow around roughened circular cylinders in transitional regimes. The results confirmed the soundness of the idea of the existence of a link between the drag coefficient of a bluff body, its pressure distribution, and the frequency of the shedding of vortices in its wake. In particular, Bearman’s number and Griffin’s number were shown to be able to describe this link with sufficient accuracy and to be a function of the Reynolds number based on the typical dimension of the surface roughness. A physical interpretation of Griffin’s number was also given which permits to link the drag force with the velocity of the potential flow at separation and the frequency of vortex shedding.

A Basic Research on the VIV Response of Rotating Circular Cylinder in Flow

2011 ◽  
Author(s):  
Chang-Kyu Rheem ◽  
Koichiro Kato
Keyword(s):  
Circular Cylinder ◽  
Natural Frequency ◽  
Vortex Shedding ◽  
Oscillation Amplitude ◽  
Water Channel ◽  
Basic Research ◽  
Rotation Frequency ◽  
Circular Cylinders ◽  
Discrete Vortex ◽  
Rotating Circular Cylinder

The characteristics of VIV response of rotating circular cylinders in flow had been investigated by both experiment and numerical simulation. In the experiment, the motions of a flexible circular cylinder pipe installed in a circulation water channel were measured. In simulation, a Discrete Vortex Method had been used to estimate hydrodynamic forces acting on a rigid circular cylinder. When a cylinder rotates in flow, a rotation frequency becomes important added to natural frequency and vortex shedding frequency. The deflection of a flexble pipe peaked when the frequency ratio of rotation frequency to natural frequency was between 1.0 and 1.5. This is similar to increment of oscillation amplitude by a resonance of natural vibration and vortex shedding. The peak oscillation frequency of a rotating circular cylinder in flow decreased with increase in rotation number. The main axis of cylinder oscillation turned in the rotation direction.

Pressure Distributions Around Circular Cylinders in Oscillating Flow

1980 ◽  
Vol 102 (2) ◽  
pp. 191-195 ◽  
Author(s):  
C. Dalton ◽  
B. Chantranuvatana
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Pressure Distribution ◽  
Vortex Shedding ◽  
Flow Reversal ◽  
Oscillatory Motion ◽  
Circular Cylinders ◽  
Oscillating Flow ◽  
Average Pressure ◽  
Pressure Distributions

Oscillatory motion of a circular cylinder is studied from the viewpoint of the average pressure distribution on the cylinder. Effects of Reynolds number up to 40,000, period, and Keulegan and Carpenter number on the pressure distribution are examined. Results are explained in terms of vortex shedding and its relationship to period and Keulegan-Carpenter number. The effects of flow reversal, sweeping wake vortices back over the cylinder, are discussed.

Vortex Shedding From Two Circular Cylinders in Staggered Arrangement

1980 ◽  
Vol 102 (2) ◽  
pp. 166-171 ◽  
Author(s):  
M. Kiya ◽  
M. Arie ◽  
H. Tamura ◽  
H. Mori
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Circular Cylinders ◽  
Staggered Arrangement

The frequency of vortex shedding from two circular cylinders of the same diameter in staggered arrangement is experimentally investigated at a Reynolds number of 1.58 × 104. This Reynolds number is within the range where the flow around a circular cylinder is relatively insensitive to Reynolds number changes. The results are summarized in several figures from which one can obtain the Strouhal number of vortex shedding for all arrangements within distances between their centers less than 5 diameters.

scholarly journals Aerodynamics of smooth and rough square-section prisms at incidence in very high Reynolds-number cross-flows

2021 ◽  
Vol 62 (3) ◽  
Author(s):  
Nils Paul van Hinsberg
Keyword(s):  
Reynolds Number ◽  
Cross Sections ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Surface Boundary ◽  
Experimental Proof ◽  
Surface Boundary Layer ◽  
Pitch Moment ◽  
The Mean ◽  
High Reynolds

Abstract The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1$$\times$$ × 10$$^{5}$$ 5 $$\le$$ ≤ Re$$_{D}$$ D $$\le$$ ≤ 1$$\times$$ × 10$$^{7}$$ 7 . For the smooth prism with $$k_s$$ k s /D = 4$$\times$$ × 10$$^{-5}$$ - 5 , tests were performed at three angles of incidence, i.e. $$\alpha$$ α = 0$$^{\circ }$$ ∘ , −22.5$$^{\circ }$$ ∘ and −45$$^{\circ }$$ ∘ , whereas only both “symmetric” angles were studied for its slightly rough counterpart with $$k_s$$ k s /D = 1$$\times$$ × 10$$^{-3}$$ - 3 . First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as $$\mathcal {O}$$ O (10$$^{7}$$ 7 ). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though. Graphic abstract

Vortex shedding from a circular cylinder in moderate-Reynolds-number shear flow

1980 ◽  
Vol 101 (4) ◽  
pp. 721-735 ◽  
Author(s):  
Masaru Kiya ◽  
Hisataka Tamura ◽  
Mikio Arie
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Shear Flow ◽  
Vortex Shedding ◽  
Transverse Velocity ◽  
Number Range ◽  
Uniform Shear ◽  
Reynolds Number Range ◽  
Moderate Reynolds Number ◽  
Shear Parameter

The frequency of vortex shedding from a circular cylinder in a uniform shear flow and the flow patterns around it were experimentally investigated. The Reynolds number Re, which was defined in terms of the cylinder diameter and the approaching velocity at its centre, ranged from 35 to 1500. The shear parameter, which is the transverse velocity gradient of the shear flow non-dimensionalized by the above two quantities, was varied from 0 to 0·25. The critical Reynolds number beyond which vortex shedding from the cylinder occurred was found to be higher than that for a uniform stream and increased approximately linearly with increasing shear parameter when it was larger than about 0·06. In the Reynolds-number range 43 < Re < 220, the vortex shedding disappeared for sufficiently large shear parameters. Moreover, in the Reynolds-number range 100 < Re < 1000, the Strouhal number increased as the shear parameter increased beyond about 0·1.

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