Uniform-shear flow over a circular cylinder at low Reynolds numbers

Kang, Sangmo

doi:10.1016/j.jfluidstructs.2006.02.003

Cited by 64 publications

(57 citation statements)

References 23 publications

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“…Numerical results obtained by Lei et al (2000) and Kang (2006) under large blockage and conditions enforcing no cross-flow velocity on the upper and lower boundaries (i.e. comparable to conditions BC2), at the same Reynolds number (Re = 100), are also reported in the table; they are close to the present results obtained with conditions BC2.…”

Section: Resultssupporting

confidence: 85%

“…In the first branch (β ∈ [0, 0.2]), C x slowly decreases as a function of β. A similar trend was observed by Lei et al (2000), Kang (2006) and Cao et al (2010) in the same range of β, at comparable Reynolds numbers. As the shear parameter is increased above 0.…”

Section: Fluid Forcessupporting

confidence: 85%

“…Vorticity contours are centred on the background vorticity induced by the oncoming shear (ω z = −β). It can be noted that the shear slightly alters the antisymmetric nature of the wake pattern, as also reported in previous works (Kang 2006;Cao et al 2010); in particular, the negative (blue) vortices are convected faster than the positive (orange) ones. However, the alternating vortex shedding pattern remains globally comparable to the vortex street developing in uniform flow and the shedding frequency, equal to f C y , is close to that observed for β = 0.…”

Section: Flow Regimessupporting

confidence: 84%

“…The case of a fixed circular cylinder placed in planar shear flow has been addressed experimentally Kwon, Sung & Hyun 1992;Sumner & Akosile 2003;Cao et al 2007) and numerically (Jordan & Fromm 1972;Yoshino & Hayashi 1984;Chew, Luo & Cheng 1997;Lei, Cheng & Kavanagh 2000;Kang 2006;Cao et al 2010). These prior studies, which mainly focused on linear shear, quantified the evolution of the vortex shedding frequency and time-averaged fluid forces as functions of the shear parameter (β), defined as the inflow velocity gradient normalized by the cylinder diameter and the oncoming flow velocity at the centre of the body.…”

Section: Introductionmentioning

confidence: 99%

“…ratio between the body diameter and the width of the test section or computational domain). Kang (2006) suggested that the influence of the blockage ratio may justify the above mentioned discrepancies. The different regimes of the unconfined flow past a fixed circular cylinder still need to be clarified, especially for large values of the shear parameter.…”

Section: Introductionmentioning

confidence: 99%

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Vortex-induced vibrations of a cylinder in planar shear flow

2017

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 18137 The system composed of a circular cylinder, either fixed or elastically mounted, and immersed in a current linearly sheared in the cross-flow direction, is investigated via numerical simulations. The impact of the shear and associated symmetry breaking are explored over wide ranges of values of the shear parameter (non-dimensional inflow velocity gradient, β ∈ [0, 0.4]) and reduced velocity (inverse of the non-dimensional natural frequency of the oscillator, U * ∈ [2, 14]), at Reynolds number Re = 100; β, U * and Re are based on the inflow velocity at the centre of the body and on its diameter. In the absence of large-amplitude vibrations and in the fixed body case, three successive regimes are identified. Two unsteady flow regimes develop for β ∈ [0, 0.2] (regime L) and β ∈ [0.2, 0.3] (regime H). They differ by the relative influence of the shear, which is found to be limited in regime L. In contrast, the shear leads to a major reconfiguration of the wake (e.g. asymmetric pattern, lower vortex shedding frequency, synchronized oscillation of the saddle point) and a substantial alteration of the fluid forcing in regime H. A steady flow regime (S), characterized by a triangular wake pattern, is uncovered for β > 0.3. Free vibrations of large amplitudes arise in a region of the parameter space that encompasses the entire range of β and a range of U * that widens as β increases; therefore vibrations appear beyond the limit of steady flow in the fixed body case (β = 0.3). Three distinct regimes of the flow-structure system are encountered in this region. In all regimes, body motion and flow unsteadiness are synchronized (lock-in condition). For β ∈ [0, 0.2], in regime VL, the system behaviour remains close to that observed in uniform current. The main impact of the shear concerns the amplification of the in-line response and the transition from figure-eight to ellipsoidal orbits. For β ∈ [0.2, 0.4], the system exhibits two well-defined regimes: VH1 and VH2 in the lower and higher ranges of U * , respectively. Even if the wake patterns, close to the asymmetric pattern observed in regime H, are comparable in both regimes, the properties of the vibrations and fluid forces clearly depart. The responses differ by their spectral contents, i.e. sinusoidal versus multi-harmonic, and their amplitudes are much larger in regime VH1, where the in-line responses reach 2 diameters (0.03 diameters in uniform flow) and the cross-flow responses 1.3 diameters. Aperiodic, intermittent oscillations are found to occur in the transition region between regimes VH1 and VH2; it appears that wake-body synchronization persists in this case.

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Section: Resultssupporting

confidence: 85%

Section: Fluid Forcessupporting

confidence: 85%

Section: Flow Regimessupporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Vortex-induced vibrations of a cylinder in planar shear flow

2017

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Shear effect on square cylinder wake transition characteristics

Lankadasu

Vengadesan

2010

Numerical Methods in Fluids

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SUMMARYThe transition of square cylinder wake flow from two-dimensional (2-D) to three-dimensional (3-D) when inflow is subjected to linear shear is examined numerically. The value of the non-dimensional shear parameter (K ) considered in this study are 0.0, 0.1, and 0.2. The range of Reynolds number (Re) defined based on the centerline velocity and cylinder width is from Re = 150 to 700. The transition of the wake flow from 2-D laminar to 3-D is marked by streamwise vortical structures. Unlike in uniform flow, in shear flow the transition is characterized by single mode of spanwise wavelength. The critical Reynolds number (Re crit ), at which the transition from 2-D to 3-D occurs, is less in case of shear flow. The magnitude of the mean lift coefficient increases with increasing shear parameter on the positive side. The strength of the Karman vortices on the top side is higher and on the bottom side is lower when compared with the same in the uniform flow.

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Turbulence in a skewed three‐dimensional wall‐bounded shear flow: effect of mean vorticity on structure modification

Holstad

Andersson

Pettersen

2011

Numerical Methods in Fluids

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SUMMARY Mean‐flow three‐dimensionalities affect both the turbulence level and the coherent flow structures in wall‐bounded shear flows. A tailor‐made flow configuration was designed to enable a thorough investigation of moderately and severely skewed channel flows. A unidirectional shear‐driven plane Couette flow was skewed by means of an imposed spanwise pressure gradient. Three different cases with 8°, 34°and 52°skewing were simulated numerically and the results compared with data from a purely two‐dimensional plane Couette flow. The resulting three‐dimensional flow field became statistically stationary and homogeneous in the streamwise and spanwise directions while the mean velocity vector V and the mean vorticity vector Ω remained parallel with the walls. Mean flow profiles were presented together with all components of the Reynolds stress tensor. The mean shear rate in the core region gradually increased with increasing skewing whereas the velocity fluctuations were enhanced in the spanwise direction and reduced in the streamwise direction. The Reynolds shear stress is known to be closely related to the coherent flow structures in the near‐wall region. The instantaneous and ensemble‐averaged flow structures were turned by the skewed mean flow. We demonstrated for the medium‐skewed case that the coherent structures should be examined in a coordinate system aligned with V to enable a sound interpretation of 3D effects. The conventional symmetry between Case 1 and Case 2 vortices was broken and Case 1 vortices turned out to be stronger than Case 2. This observation is in conflict with the common understanding on the basis of the spanwise (secondary) mean shear rate. A refined model was proposed to interpret the structure modifications in three‐dimensional wall‐flows. What matters is the orientation of the mean vorticity vector Ω relative to the vortex vorticity vector ωv, that is, the sign of Ω ·ωv. In the present situation, Ω ·ωv > 0 for the Case 1 vortices causing a strengthening relative to the Case 2 vortices. Copyright © 2011 John Wiley & Sons, Ltd.

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Uniform-shear flow over a circular cylinder at low Reynolds numbers

Cited by 64 publications

References 23 publications

Vortex-induced vibrations of a cylinder in planar shear flow

Vortex-induced vibrations of a cylinder in planar shear flow

Shear effect on square cylinder wake transition characteristics

Turbulence in a skewed three‐dimensional wall‐bounded shear flow: effect of mean vorticity on structure modification

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