A study of forces, circulation and vortex patterns around a circular cylinder in oscillating flow

1988 ◽  
Vol 196 ◽  
pp. 467-494 ◽  
Author(s):  
E. D. Obasaju ◽  
P. W. Bearman ◽  
J. M. R. Graham
Keyword(s):  
Circular Cylinder ◽  
Steady Flow ◽  
Correlation Length ◽  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Transverse Force ◽  
Vortex Street ◽  
Oscillating Flow ◽  
Time Histories ◽  
Vortex Patterns

Measurements of sectional and total forces and the spanwise correlation of vortex shedding are presented for a circular cylinder in planar oscillatory flow at Keulegan-Carpenter numbers, KC, in the range from about 4 to 55. The viscous parameter β is in the range from around 100 to 1665. Circulation measurements around a circuit close to and enclosing the cylinder, are also presented. A mode-averaging technique was used for both sectional forces and circulation measurements and this gave, for typical modes of vortex shedding, time histories over an average cycle. The transverse force and the circulation tend to fluctuate in sympathy with each other, except around the instant of flow reversal when the force changes sign but the circulation remains high. Values of the strength of shed vortices, estimated from the measured circulation, are found to be comparable with steady-flow results. For KC [lsim ] 30, modes of vortex shedding occur over distinct ranges of KC with spanwise correlation high at the centre of a KC-range for a particular mode of shedding but low at the boundaries. Above KC ≈ 30 the correlation is no longer very sensitive to KC and the correlation length is estimated to be equal to 4.65 cylinder diameters. In the transverse vortex-street regime (8 [lsim ] KC [lsim ] 15) the cylinder was found to experience a steady transverse force, the coefficient of which is estimated to be about 0.5 at KC = 14.

Oscillatory flow past a circular cylinder in a rotating frame

1997 ◽  
Vol 345 ◽  
pp. 101-131
Author(s):  
M. D. KUNKA ◽  
M. R. FOSTER
Keyword(s):  
Circular Cylinder ◽  
Steady Flow ◽  
Stagnation Point ◽  
Oscillatory Flow ◽  
Numerical Solutions ◽  
Initial Conditions ◽  
Temporal Integration ◽  
Oncoming Flow ◽  
Flow Past ◽  
Rear Stagnation Point

Because of the importance of oscillatory components in the oncoming flow at certain oceanic topographic features, we investigate the oscillatory flow past a circular cylinder in an homogeneous rotating fluid. When the oncoming flow is non-reversing, and for relatively low-frequency oscillations, the modifications to the equivalent steady flow arise principally in the ‘quarter layer’ on the surface of the cylinder. An incipient-separation criterion is found as a limitation on the magnitude of the Rossby number, as in the steady-flow case. We present exact solutions for a number of asymptotic cases, at both large frequency and small nonlinearity. We also report numerical solutions of the nonlinear quarter-layer equation for a range of parameters, obtained by a temporal integration. Near the rear stagnation point of the cylinder, we find a generalized velocity ‘plateau’ similar to that of the steady-flow problem, in which all harmonics of the free-stream oscillation may be present. Further, we determine that, for certain initial conditions, the boundary-layer flow develops a finite-time singularity in the neighbourhood of the rear stagnation point.

Oscillating Flow Past a Rigid Circular Cylinder: A Finite-Difference Calculation

1991 ◽  
Vol 113 (3) ◽  
pp. 377-383 ◽  
Author(s):  
Xuegeng Wang ◽  
Charles Dalton
Keyword(s):  
Reynolds Number ◽  
Finite Difference ◽  
Circular Cylinder ◽  
Physical Interpretation ◽  
Oscillating Flow ◽  
Flow Past ◽  
Dependent Variables ◽  
Good Comparison ◽  
Vortex Patterns ◽  
Difference Calculation

A finite-difference study of the sinusoidally oscillating flow past a fixed circular cylinder is made using vorticity and stream function as the dependent variables. Calculations are performed for conditions which lead to both a symmetric wake and an unsymmetric wake. The Reynolds number ranges from 100 to 3000 and the Keulegan-Carpenter number ranges from 1 to 12. A hybrid differencing scheme is introduced to provide a stable for large values of the parameters. Good comparison to flow visualization results and calculated force coefficients is found. The results are given a physical interpretation for the various vortex patterns observed.

Vortex shedding and lock-on of a circular cylinder in oscillatory flow

1986 ◽  
Vol 170 ◽  
pp. 527-544 ◽  
Author(s):  
C. Barbi ◽  
D. P. Favier ◽  
C. A. Maresca ◽  
D. P. Telionis
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Published Data ◽  
Bluff Bodies ◽  
Driving Frequency ◽  
Frequency Limit ◽  
Mean Velocity ◽  
Shedding Frequency ◽  
Friction Measurements

An experimental study has been made of a circular cylinder in steady and oscillatory flow with non-zero mean velocity up to a Reynolds number of 40000. The results for the stationary cylinder are in close agreement with previously published data. Skin-friction measurements revealed the amplitude of fluctuation of the boundary layer for different angular locations. It has been universally accepted that bluff bodies shed vortices at their natural frequency of shedding (Strouhal frequency), or, when synchronized with an external unsteadiness, at the frequency of the disturbance or half of it, depending of the direction of the unsteadiness. Our findings, instead, indicate that the shedding frequency may vary smoothly with the driving frequency before locking on its subharmonic. Moreover, the present results indicate that, at the lowest frequency limit of lock-on, vortices are shed simultaneously on both sides of the model. A more traditional alternate pattern of vortex shedding is then recovered at higher driving frequencies.

scholarly journals Exotic wakes of an oscillating circular cylinder: how singles pair up

2021 ◽  
Vol 922 ◽  
Author(s):  
Kerry Hourigan
Keyword(s):  
Reynolds Number ◽  
Fluid Flow ◽  
Circular Cylinder ◽  
Numerical Simulations ◽  
Vortex Street ◽  
Wake Vortex ◽  
Continuous Evolution ◽  
Vortex Patterns ◽  
Sudden Jump ◽  
Uniform Fluid

Fascinating wake vortex patterns emerge when a circular cylinder is forced to vibrate laterally to a uniform fluid flow, deviating from the well-known Kármán vortex street and first reported by Williamson & Roshko (J. Fluids Struct., vol. 2, 1988, pp. 355–381). The two rows of single vortices (2S mode) can suddenly transition to a row of paired vortices and a row of single vortices (P+S mode) as the forcing amplitude is increased. Further increase in amplitude finds another sudden jump back to the 2S mode. Through a series of elegant and carefully crafted numerical simulations, Matharu et al. (J. Fluid Mech., vol. 918, 2021, A42) determine that the transitions occur via bifurcations, but that underlying these observed ‘jumps’, a continuous evolution of the vortex street between the modes is seen along unstable branches connecting the two modes. As the Reynolds number decreases from 100, bistability and the P+S mode are eventually suppressed.

scholarly journals FORCES ON ROUGH-WALLED CIRCULAR CYLINDERS

1976 ◽  
Vol 1 (15) ◽  
pp. 134 ◽  
Author(s):  
Turgut Sarpkaya
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Least Squares Method ◽  
Reynolds Numbers ◽  
Transverse Force ◽  
Circular Cylinders ◽  
Mean Square ◽  
Relative Roughness

This paper presents the results of an extensive experimental investigation of the in-line and transverse forces acting on sand-roughened circular cylinders placed in oscillatory flow at Reynolds numbers up to 1,500,000, Keulegan-Carpenter numbers up to 100, and relative roughnesses from 1/800 to 1/50. The drag and inertia coefficients have been determined through the use of the Fourier analysis and the least squares method. The transverse force (lift) has been analysed in terms of its maximum and root-mean-square values. In addition, the frequency of vortex shedding and the Strouhal number have been determined. The results have shown that all of the coefficients cited above are functions of the Reynolds number, Keulegan-Carpenter number, and the relative roughness height. The results have also shown that the effect of roughness is quite profound and that the drag coefficients obtained from tests in steady flow are not applicable to harmonic flows even when the loading is predominantly drag.

Numerical investigation of the oscillatory flow around a circular cylinder close to a wall at moderate Keulegan–Carpenter and low Reynolds numbers

2009 ◽  
Vol 627 ◽  
pp. 259-290 ◽  
Author(s):  
PIETRO SCANDURA ◽  
VINCENZO ARMENIO ◽  
ENRICO FOTI
Keyword(s):  
Circular Cylinder ◽  
Oscillatory Flow ◽  
Three Dimensional ◽  
Hydrodynamic Forces ◽  
Transverse Force ◽  
Vortex Structures ◽  
Time Development ◽  
Two Dimensional ◽  
Wide Range ◽  
Three Dimensional Simulations

The oscillatory flow around a circular cylinder close to a plane wall is investigated numerically, by direct numerical simulation of the Navier–Stokes equations. The main aim of the research is to gain insight into the effect of the wall on the vorticity dynamics and the forces induced by the flow over the cylinder. First, two-dimensional simulations are performed for nine values of the gap-to-diameter ratio e. Successively, three-dimensional simulations are carried out for selected cases to analyse the influence of the gap on the three-dimensional organization of the flow. An attempt to explain the pressure distribution around the cylinder in terms of vorticity time development is presented. Generally, the time development of the hydrodynamic forces is aperiodic (i.e. changes from cycle to cycle). In one case (Re = 200), when the distance of the cylinder from the wall is reduced, the behaviour of the flow changes from aperiodic to periodic. When the cylinder approaches the wall the drag coefficient of the in-line force increases in a qualitative agreement with the results reported in literature. The transverse force is not monotonic with the reduction of the gap: it first decreases down to a minimum, and then increases with a further reduction of the gap. For intermediate values of the gap the decrease of the transverse force is due to the reduction of the angle of ejection of the shedding vortices caused by the closeness of the wall; for small gaps the increase of the transverse force is due to the strong interaction between the vortex system ejected from the cylinder and the shear layer generated on the wall.Three-dimensional simulations show that the flow is unstable with respect to spanwise perturbations which cause the development of three-dimensional vortices and the distortion of the two-dimensional ones generated by flow separation.In all the analysed cases, the three-dimensional effects on the hydrodynamic forces are clearly attenuated when the cylinder is placed close to the wall.The spanwise modulation of the vortex structures induces oscillations of the sectional forces along the axis of the cylinder which in general are larger for the transverse sectional force. In the high-Reynolds-number case (Re = 500), the reduction of the gap produces a large number of three-dimensional vortex structures developing over a wide range of spatial scales. This produces homogenization of the flow field along the spanwise direction and a consequent reduction of the amplitudes of oscillation of the sectional forces.

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.

On the Impact of the Addition of Steady Flow to Oscillatory Flow in a Diffuser

2008 ◽  
Author(s):  
Cameron V. King ◽  
Barton L. Smith
Keyword(s):  
Pressure Gradient ◽  
Steady Flow ◽  
Oscillatory Flow ◽  
Adverse Pressure Gradient ◽  
Oscillating Flow ◽  
Pressure Measurements ◽  
Minor Losses ◽  
Velocity Pressure ◽  
The Impact ◽  
Diffuser Angle

Separating oscillating and pulsating flows in an internal adverse pressure gradient geometry are studied experimentally. Simultaneous velocity-pressure measurements demonstrate that the minor losses associated with oscillating flow in an adverse pressure gradient geometry can be smaller or larger than for steady flow. The minor losses grow with increasing displacement amplitude in the range 10 < L0/h < 37. Losses decrease with Reδ in the range of 380 < Re < 740. The extent and duration of boundary separation increase with L0/h. It is found that the losses increase with increasing diffuser angle for 12° < θ < 30°. The addition of steady flow can cause the in decrease if the flow becomes more turbulent as a result, or increase when the flow was already turbulent.

Oscillatory flow regimes for a circular cylinder near a plane boundary

2018 ◽  
Vol 844 ◽  
pp. 127-161 ◽  
Author(s):  
Chengwang Xiong ◽  
Liang Cheng ◽  
Feifei Tong ◽  
Hongwei An
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Flow Regimes ◽  
Plane Boundary ◽  
Marginal Stability ◽  
Hysteresis Phenomenon ◽  
Physical Mechanisms ◽  
Large Hysteresis

Oscillatory flow around a circular cylinder close to a plane boundary is numerically investigated at low-to-intermediate Keulegan–Carpenter ($KC$) and Stokes numbers ($\unicode[STIX]{x1D6FD}$) for different gap-to-diameter ratios ($e/D$). A set of unique flow regimes is observed and classified based on the established nomenclature in the ($KC,\unicode[STIX]{x1D6FD}$)-space. It is found that the flow is not only influenced by $e/D$ but also by the ratio of the thickness of the Stokes boundary layer ($\unicode[STIX]{x1D6FF}$) to the gap size (e). At relatively large $\unicode[STIX]{x1D6FF}/e$ values, vortex shedding through the gap is suppressed and vortices are only shed from the top of the cylinder. At intermediate values of $\unicode[STIX]{x1D6FF}/e$, flow through the gap is enhanced, resulting in horizontal gap vortex shedding. As $\unicode[STIX]{x1D6FF}/e$ is further reduced below a critical value, the influence of $\unicode[STIX]{x1D6FF}/e$ becomes negligible and the flow is largely dependent on $e/D$. A hysteresis phenomenon is observed for the transitions in the flow regime. The physical mechanisms responsible for the hysteresis and the variation of marginal stability curves with $e/D$ are explored at $KC=6$ through specifically designed numerical simulations. The Stokes boundary layer over the plane boundary is found to be responsible for the relatively large hysteresis range over $0.25<e/D<1.0$. Three mechanisms have been identified to the change of the marginal stability curve over $e/D$, which are the blockage effect due to the geometry setting, the favourable pressure gradient over the gap and the location of the leading eigenmode relative to the cylinder.

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