scholarly journals Forces Acting on a Pair of Circular Cylinders Arranged Side by Side in the Region of Critical Reynolds Number

2004 ◽  
Vol 52 (611) ◽  
pp. 556-563
Author(s):  
Nobuyuki Okura ◽  
Hidetoshi Hayafuji ◽  
Muneshige Okude
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Circular Cylinders

Onset of Vortex Shedding in a Periodic Array of Circular Cylinders

2006 ◽  
Vol 128 (5) ◽  
pp. 1101-1105 ◽  
Author(s):  
L. Zhang ◽  
S. Balachandar
Keyword(s):  
Reynolds Number ◽  
Hopf Bifurcation ◽  
Vortex Shedding ◽  
Critical Reynolds Number ◽  
Base Flow ◽  
Periodic Array ◽  
Circular Cylinders ◽  
Rectangular Cylinders

Hopf bifurcation of steady base flow and onset of vortex shedding over a transverse periodic array of circular cylinders is considered. The influence of transverse spacing on critical Reynolds number is investigated by systematically varying the gap between the cylinders from a small value to large separations. The critical Reynolds number behavior for the periodic array of circular cylinders is compared with the corresponding result for a periodic array of long rectangular cylinders considered in [Balanchandar, S., and Parker, S. J., 2002, “Onset of Vortex Shedding in an Inline and Staggered Array of Rectangular Cylinders,” Phys. Fluids, 14, pp. 3714–3732]. The differences between the two cases are interpreted in terms of differences between their wake profiles.

Experiment on smooth, circular cylinders in cross-flow in the critical Reynolds number regime

2011 ◽  
Vol 51 (4) ◽  
pp. 949-967 ◽  
Author(s):  
J. J. Miau ◽  
H. W. Tsai ◽  
Y. J. Lin ◽  
J. K. Tu ◽  
C. H. Fang ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Cross Flow ◽  
Circular Cylinders

The Forces acting on a Pair of Circular Cylinders Arranged Side by Side near the Critical Reynolds Number

2002 ◽  
Vol 2002.51 (0) ◽  
pp. 37-38
Author(s):  
Ryo IMAI ◽  
Kazuhiko KATO ◽  
Nobuyuki OHKURA ◽  
Hidetoshi HAYAFUJI ◽  
Muneshige OKUDE
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Circular Cylinders

Critical Reynolds number and galloping instabilities: experiments on circular cylinders

2011 ◽  
Vol 52 (5) ◽  
pp. 1295-1306 ◽  
Author(s):  
N. Nikitas ◽  
J. H. G. Macdonald ◽  
J. B. Jakobsen ◽  
T. L. Andersen
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Circular Cylinders

Cell structure on circular cylinders near the critical Reynolds number

1998 ◽  
Author(s):  
Takashi Yoshinaga ◽  
Mamoru Sato ◽  
Atsushi Tate ◽  
Norikazu Sudani ◽  
Kunio Soga
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Cell Structure ◽  
Circular Cylinders

Linear instability of annular Poiseuille flow

2008 ◽  
Vol 610 ◽  
pp. 391-406 ◽  
Author(s):  
C. J. HEATON
Keyword(s):  
Reynolds Number ◽  
Poiseuille Flow ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Linear Instability ◽  
Circular Cylinders ◽  
Flow Profile ◽  
Mean Flow ◽  
Annular Pipe ◽  
Axisymmetric Disturbances

The linear stability of flow along an annular pipe formed by two coaxial circular cylinders is considered. We find that the flow is unstable above a critical Reynolds number for all 0 < η ≤ 1, where η is the ratio between the radii of the inner and outer cylinders. This contradicts a recent claim that the flow is stable at all Reynolds numbers for radius ratio η less than a finite critical value. We find that non-axisymmetric disturbances become stable at all Reynolds numbers for η < 0.11686215, and we are able to study this ‘bifurcation from infinity’ asymptotically. However, axisymmetric disturbances remain unstable, with critical Reynolds number tending to infinity as η → 0. A second asymptotic analysis is performed to show that the critical Reynolds number Rec ∝ η−1 log(η−1) as η → 0, with the form of the mean flow profile causing the appearance of the logarithm. The stability of Hagen–Poiseuille flow (η = 0) at all Reynolds numbers is therefore interpreted as a limit result, and there are no annular pipe flows which share this stability.

Secondary instabilities in the flow around two circular cylinders in tandem

2010 ◽  
Vol 644 ◽  
pp. 395-431 ◽  
Author(s):  
BRUNO S. CARMO ◽  
JULIO R. MENEGHINI ◽  
SPENCER J. SHERWIN
Keyword(s):  
Reynolds Number ◽  
Stability Analysis ◽  
Numerical Simulations ◽  
Critical Reynolds Number ◽  
Three Dimensional ◽  
Circular Cylinders ◽  
Physical Mechanisms ◽  
Nonlinear Character ◽  
Secondary Instabilities ◽  
Wake Transition

Direct stability analysis and numerical simulations have been employed to identify and characterize secondary instabilities in the wake of the flow around two identical circular cylinders in tandem arrangements. The centre-to-centre separation was varied from 1.2 to 10 cylinder diameters. Four distinct regimes were identified and salient cases chosen to represent the different scenarios observed, and for each configuration detailed results are presented and compared to those obtained for a flow around an isolated cylinder. It was observed that the early stages of the wake transition changes significantly if the separation is smaller than the drag inversion spacing. The onset of the three-dimensional instabilities were calculated and the unstable modes are fully described. In addition, we assessed the nonlinear character of the bifurcations and physical mechanisms are proposed to explain the instabilities. The dependence of the critical Reynolds number on the centre-to-centre separation is also discussed.

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

Stability of thermocapillary flows in non-cylindrical liquid bridges

2002 ◽  
Vol 458 ◽  
pp. 35-73 ◽  
Author(s):  
CH. NIENHÜSER ◽  
H. C. KUHLMANN
Keyword(s):  
Reynolds Number ◽  
Prandtl Number ◽  
Critical Reynolds Number ◽  
Volume Fraction ◽  
Thermocapillary Flow ◽  
Surface Shape ◽  
Liquid Bridges ◽  
Gravity Level ◽  
Neutral Curves ◽  
Prandtl Numbers

The thermocapillary flow in liquid bridges is investigated numerically. In the limit of large mean surface tension the free-surface shape is independent of the flow and temperature fields and depends only on the volume of liquid and the hydrostatic pressure difference. When gravity acts parallel to the axis of the liquid bridge the shape is axisymmetric. A differential heating of the bounding circular disks then causes a steady two-dimensional thermocapillary flow which is calculated by a finite-difference method on body-fitted coordinates. The linear-stability problem for the basic flow is solved using azimuthal normal modes computed with the same discretization method. The dependence of the critical Reynolds number on the volume fraction, gravity level, Prandtl number, and aspect ratio is explained by analysing the energy budgets of the neutral modes. For small Prandtl numbers (Pr = 0.02) the critical Reynolds number exhibits a smooth minimum near volume fractions which approximately correspond to the volume of a cylindrical bridge. When the Prandtl number is large (Pr = 4) the intersection of two neutral curves results in a sharp peak of the critical Reynolds number. Since the instabilities for low and high Prandtl numbers are markedly different, the influence of gravity leads to a distinctly different behaviour. While the hydrostatic shape of the bridge is the most important effect of gravity on the critical point for low-Prandtl-number flows, buoyancy is the dominating factor for the stability of the flow in a gravity field when the Prandtl number is high.

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