• 한국전산유체공학회:학술대회논문집
• /
• 2008.03a
• /
• pp.316-320
• /
• 2008

In this paper, the near wake of stationary and transversely oscillating square section cylinders with different corner radii are studied by numerical method to investigate the influence of corner radius. Six models R/D=0,0.1,0.2,0.3,0.4,0.5 (R is the corner radius and D is the characteristic dimension of the body) were studied. It was found that the corner radius of square cylinder significantly influences the flow features around the body both in stationary and oscillating conditions. Results indicate that, as R/D ratio increases, the Strouhal number increases and the separation point decrease for the stationary and oscillating cases.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.10a
• /
• pp.316-320
• /
• 2008

In this paper, the near wake of stationary and transversely oscillating square section cylinders with different corner radii are studied by numerical method to investigate the influence of corner radius. Six models R/D=0,0.1,0.2,0.3,0.4,0.5 (R is the corner radius and D is the characteristic dimension of the body) were studied. It was found that the corner radius of square cylinder significantly influences the flow features around the body both in stationary and oscillating conditions. Results indicate that, as R/D ratio increases, the Strouhal number increases and the separation point decrease for the stationary and oscillating cases.

• 한국전산유체공학회:학술대회논문집
• /
• 2007.10a
• /
• pp.115-119
• /
• 2007

In this paper, a flow visualization analysis has been carried out on an oscillating square section cylinder, numerically, using a commercially available code CFD-ACE. In this study, the square cylinder is forced to oscillate at different frequencies of excitation, viz., fe/fo=0.5, 1.0 and 2.0 (where, fe is the excitation frequency provided to the cylinder and fo is the natural vortex shedding frequency from the stationary cylinder at a particular Reynolds number (=5200). In all the cases, the peak-to-peak amplitude of oscillation is kept at 32% of the side dimension of the square cylinder. These studies are conducted to understand the influence of frequency of oscillation on the flow field features around the cylinder, particularly the mode of vortex shedding. Results indicate that, the flow field around a square cylinder is very much influenced by the excitation frequency, in particular the vortex shedding mode. It is also found that, the vortex street parameters are significantly influence by the oscillation frequency. Comparison with earlier reported experimental studies has also been attempted in this paper. In appears that, such a numerical exercise (as performed in this paper) is first of its kind. It is believed that, these studies would enable one to understand the mechanisms underlying the flow-induced vibrations of a square section cylinder.

• Wind and Structures
• /
• v.34 no.5
• /
• pp.437-450
• /
• 2022

Vortex-induced vibration (VIV) is a significant concern when designing slender structures with square cross sections. VIV strongly depends on structural dynamics and flow states, which depend on the conditions of the approaching flow and shape of a structure. Therefore, the effects of the angle of attack on the coupling effects of VIV for a square cylinder are expected to be significant in practice. In this study, the aerodynamic forces for a fixed and elastically mounted square cylinder were measured using wind pressure tests. Aerodynamic forces on the stationary cylinder are firstly discussed by comparisons of variation of statistical aerodynamic force and wind pressure coefficient with wind angle of attack. The coupling effect between the aerodynamic forces and the motion of the oscillating square cylinder by VIV is subsequently investigated in detail at typical wind angels of attack with occurrence of three typical flow regimes, i.e., leading-edge separation, separation bubble (reattachment), and attached flow. The coupling effect are illustrated by discussing the onset of VIV, characteristics of aerodynamic forces during VIV, and interaction between motion and aerodynamic forces. The results demonstrate that flow states can be classified based on final separation points or the occurrence of reattachment. These states significantly influence coupling effects of the oscillating cylinder. Vibration enhances vortex shedding, which creates strong fluctuations in aerodynamic forces. However, differences in the lock-in range, aerodynamic force, and interaction process for angles of attack smaller and larger than the critical angle of attack revealed noteworthy characteristics in the VIV of a square cylinder.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.11
• /
• pp.1527-1534
• /
• 2001

Phase averaged velocity fields in the near wake region behind a square cylinder have been (successfully) obtained using randomly sampled PIV data sets. The Reynolds number based on the flow velocity and the vertex height was 3,900. To identify the phase information, we examined the magnitude of circulation and the center of peak vorticity. The center of vorticity was estimated from lowpass filtered vorticity contours (LES decomposition) adopting a sub-pixel searching algirithm. Due to the sinusoidal nature of firculation which is closely related to the instantaneous vorticity, the location of peak voticity fits well with a sine curve of the circulation magnitude. Conditionally-averaged velocity fields represent the barman vortex shedding phenomenon very well within 5 degrees phase uncertainty. The oscillating nature of the separated shear layer and the separation bubble at the top surface are clearly observed. With the hot-wire measurements of Strouhal frequency, we found thats the convection velocity changes its magnitude very rapidly from 25 to 75 percent of the free stream velocity along the streamwise direction when the flow passes by the recirculation region.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.5
• /
• pp.573-583
• /
• 1998

Effects of the oscillating incoming flow on vortex shedding and lock-on behind a square cylinder are investigated using numerical simulations at a Reynolds number of 100. Vortex shedding occurred at low forcing frequencies of the incoming flow similar to the natural vortex shedding. As the forcing frequency further increases, the shedding frequency decreases to the half of the forcing freqnency. For a sufficiently large frequency, vortex shedding returns to the natural vortex shedding irrespective of the forcing amplitude. Also, the lock-on region becomes wider with higher forcing amplitudes. The phase diagram between the drag and lift shows a simple periodic behavior in the lock-on region, while a complicated periodic phase relation is observed when there is no lock-on.

• Wind and Structures
• /
• v.2 no.4
• /
• pp.285-303
• /
• 1999

A discrete vortex method (DVM) has been developed at the Department of Aerospace Engineering, University of Glasgow, to predict unsteady, incompressible, separated flows around closed bodies. The basis of the method is the discretisation of the vorticity field, rather than the velocity field, into a series of vortex particles that are free to move in the flow. This paper gives a brief description of the method and presents the results of calculations on static and transversely oscillating square section cylinders. The results demonstrate that the method successfully predicts the character of the flow field at different angles of incidence for the static case. Vortex lock-in around the resonance point is successfully captured in the oscillatory cases. It is concluded that the vortex method results show good agreement, both qualitatively and quantitatively, with results from various experimental data.