Characteristics of force coefficients and energy transfer for vortex shedding modes of a square cylinder subjected to inline excitation

AbstractThe behaviour of vortices induced by a single square cylinder in an oscillating flow was investigated. The flow patterns in the vicinity of square cylinders were visualized using an in-house numerical model. Meanwhile, force coefficients exerted on the square cylinder were determined numerically. In terms of various Keulegan-Carpenter (KC) numbers, it turns out that the flow patterns for an oscillating flow past a single cylinder can be divided into three modes: (i) no vortex, (ii) pairs of symmetric vortices, and (iii) asymmetric vortex shedding. Reynolds (Re) number did not affect the flow field apparently in this study. In addition, the in-line force coefficient decreases exponentially as KC increases. Spectrum analysis of in-line force coefficients for various KCs was provided. It can be found that the flow system was at a periodic state at small KC for the first two modes. Variations of the flow system from a periodic state to a highly nonlinear state in which asymmetric vortex shedding appeared were demonstrated for increasing KC. The relationship between the in-line force and KC was provided for future applications.

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Near-Wake Flow Structures of a Corner-Chamfered Square Cylinder at Higher Harmonic Excitations

Volume 1A: Symposia, Part 2 ◽

10.1115/ajkfluids2015-12675 ◽

2015 ◽

Author(s):

M. S. Aswathy ◽

K. K. Amrita ◽

C. M. Hariprasad ◽

R. Ajith Kumar

Keyword(s):

Vortex Shedding ◽

Water Channel ◽

Wake Flow ◽

Flow Structures ◽

Square Cylinder ◽

Near Wake ◽

Harmonic Excitations ◽

Vortex Shedding Frequency ◽

Higher Harmonic ◽

Vortex Shedding Modes

In this paper, the results of a flow visualization study on the flow structures around a chamfered square cylinder are presented. Square cylinders having side dimension Bo with corner chamfering ‘b’ are used such that b/Bo ratio assumes values 0, 0.1, 0.2 and 0.3. Corners of the square cylinder are equally cut by a measure ‘b’ both in the stream-wise and cross stream directions. Flow over these cylinders are visualized in a water channel. All the studies correspond to a Reynolds number value of 2100 (based on Bo). Results are taken for two situations (a) cylinders are stationary and (b) cylinders are oscillated at frequency ‘fe’. The main objective of this study is to investigate the near-wake flow structures around the cylinders at harmonic and higher harmonic excitations. Experiments were conducted for fe/fs= 1.0, 1.5, 2.0, 2.5 and 3.0 where fs is the vortex shedding frequency from the stationary cylinder for each b/Bo ratio. Peak-to-peak amplitude of excitation is kept at 1B in all cases. In this investigation, the main focus is on investigating the vortex shedding modes, mechanisms and the number of vortices shed per shear layer as the cylinder completes one oscillatory cycle as a function of fe/fs ratio.

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Evolution of unstable system.

JOURNAL OF ADVANCES IN PHYSICS ◽

10.24297/jap.v9i3.1349 ◽

2015 ◽

Vol 9 (3) ◽

pp. 2487-2502 ◽

Cited By ~ 1

Author(s):

Igor V. Lebed

Keyword(s):

Reynolds Number ◽

Vortex Shedding ◽

Stokes Flow ◽

Stable Solution ◽

The State ◽

Unstable System ◽

Unstable Flow ◽

Unstable Solutions ◽

Vortex Shedding Modes ◽

Hydrodynamics Equations

Scenario of appearance and development of instability in problem of a flow around a solidÂ sphere at rest is discussed. The scenario was created by solutions to the multimomentÂ hydrodynamics equations, which were applied to investigate the unstable phenomena. TheseÂ solutions allow interpreting Stokes flow, periodic pulsations of the recirculating zone in the wakeÂ behind the sphere, the phenomenon of vortex shedding observed experimentally. In accordanceÂ with the scenario, system loses its stability when entropy outflow through surface confining theÂ system cannot be compensated by entropy produced within the system. The system does not findÂ a new stable position after losing its stability, that is, the system remains further unstable. AsÂ Reynolds number grows, one unstable flow regime is replaced by another. The replacement isÂ governed tendency of the system to discover fastest path to depart from the state of statisticalÂ equilibrium. This striving, however, does not lead the system to disintegration. Periodically,Â reverse solutions to the multimoment hydrodynamics equations change the nature of evolutionÂ and guide the unstable system in a highly unlikely direction. In case of unstable system, unlikelyÂ path meets the direction of approaching the state of statistical equilibrium. Such behavior of theÂ system contradicts the scenario created by solutions to the classic hydrodynamics equations.Â Unstable solutions to the classic hydrodynamics equations are not fairly prolonged along time toÂ interpret experiment. Stable solutions satisfactorily reproduce all observed stable medium states.Â As Reynolds number grows one stable solution is replaced by another. They are, however,Â incapable of reproducing any of unstable regimes recorded experimentally. In particular, stableÂ solutions to the classic hydrodynamics equations cannot put anything in correspondence to anyÂ of observed vortex shedding modes. In accordance with our interpretation, the reason for this isthe classic hydrodynamics equations themselves.

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COMPARISON OF LES WITH DSM, k-ε AND EXPERIMENTS FORTURBULENT VORTEX SHEDDING FLOW PAST 2D SQUARE CYLINDER

Journal of Structural and Construction Engineering (Transactions of AIJ) ◽

10.3130/aijs.59.49_2 ◽

1994 ◽

Vol 59 (459) ◽

pp. 49-56 ◽

Cited By ~ 1

Author(s):

Shigehiro SAKAMOTO ◽

Akashi MOCHIDA ◽

Shuzo MURAKAMI ◽

Wolfgang RODI

Keyword(s):

Vortex Shedding ◽

Square Cylinder ◽

Flow Past

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Effect of Thermal Buoyancy on Vortex-Shedding and Aerodynamic Characteristics for Fluid Flow Past an Inclined Square Cylinder

International Journal of Heat and Technology ◽

10.18280/ijht.380223 ◽

2020 ◽

Vol 38 (2) ◽

pp. 463-471

Author(s):

Md. Reyaz Arif ◽

Nadeem Hasan

Keyword(s):

Fluid Flow ◽

Vortex Shedding ◽

Aerodynamic Characteristics ◽

Square Cylinder ◽

Thermal Buoyancy ◽

Flow Past

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Vortex-induced vibrations of a long flexible circular cylinder

Journal of Fluid Mechanics ◽

10.1017/s0022112093001533 ◽

1993 ◽

Vol 250 ◽

pp. 481-508 ◽

Cited By ~ 230

Author(s):

D. Brika ◽

A. Laneville

Keyword(s):

Circular Cylinder ◽

Flow Velocity ◽

Vortex Shedding ◽

Abrupt Change ◽

Velocity Range ◽

End Effects ◽

Synchronization Region ◽

Vortex Induced Vibrations ◽

Set Up ◽

Vortex Shedding Modes

In an experimental study of the vortex-induced oscillations of a long flexible circular cylinder, the observed stationary amplitudes describe an hysteresis loop partially different from earlier studies. Each branch of the loop is associated with a vortex shedding mode and, as a jump from one branch to the other occurs, the phase difference between the cylinder displacement and the vortex shedding undergoes an abrupt change. The critical flow velocities at which the jump occurs concur with the flow visualization observations of Williamson & Roshko (1988) on the vortex shedding modes near the fundamental synchronization region. Impulsive regimes, obtained at a given flow velocity with the cylinder initially at rest or pre-excited, and progressive regimes resulting from a variation of the flow velocity, are examined. The occurrence of bifurcations is detected for a flow velocity range in the case of the impulsive regimes. The coordinates of the bifurcations define a boundary between two vortex shedding modes, a boundary that verifies the critical curve obtained by Williamson & Roshko (1988). The experimental set-up of this study simulates half the wavelength of a vibrating cable, eliminates the end effects present in oscillating rigid cylinder set-up and has one of the lowest damping ratios reported for the study of this phenomenon.

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