A critical review of the intrinsic nature of vortex-induced vibrations

The control of flow separation by periodic excitation

Fluctuating lift on a circular cylinder: review and new measurements

Results are reported from a highly accurate, global numerical stability analysis of the periodic wake of a circular cylinder for Reynolds numbers between 140 and 300 The analysis shows that the two-dimensional wake becomes (absolutely) linearly unstable to three-dimensional perturbations at a critical Reynolds number of 1885±10 The critical spanwise wavelength is 396 ± 002 diameters and the critical Floquet mode corresponds to a ‘Mode A’ instability At Reynolds number 259 the two-dimensional wake becomes linearly unstable to a second branch of modes with wavelength 0822 diameters at onset Stability spectra and corresponding neutral stability curves are presented for Reynolds numbers up to 300

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Three-dimensional Floquet stability analysis of the wake of a circular cylinder

Flow over a circular cylinder at Reynolds number 3900 is studied numerically using the technique of large eddy simulation. The computations are carried out with a high-order accurate numerical method based on B-splines and compared with previous upwind-biased and central finite-difference simulations and with the existing experimental data. In the very near wake, all three simulations are in agreement with each other. Farther downstream, the results of the B-spline computations are in better agreement with the hot-wire experiment of Ong and Wallace [Exp. Fluids 20, 441–453 (1996)] than those obtained in the finite-difference simulations. In particular, the power spectra of velocity fluctuations are in excellent agreement with the experimental data. The impact of numerical resolution on the shear layer transition is investigated.

Numerical studies of flow over a circular cylinder at ReD=3900

The fine scale three-dimensional structures usually associated with streamwise vortices in the near wake of a circular cylinder have been studied at Reynolds numbers ranging from 170 to 2200. Spatially continuous velocity measurements along lines parallel to the cylinder axis were obtained with a scanning laser anemometer. To detect the streamwise vortices in the amplitude modulated velocity field, it was necessary to develop a spatial decomposition technique to split the total flow into a primary flow component and a secondary flow component. The primary flow is comprised of the mean flow and Strouhal vortices, while the secondary flow is the result of the three-dimensional streamwise vortices that are the essence of transition to turbulence. The three-dimensional flow amplitude increases in the primary vortex formation region, then saturates shortly after the maximum amplitude in the primary flow is reached. In the near-wake region the wavelength decreases approximately like Re(exp -0.5), but increases with downstream distance. A discontinuous increase in wavelength occurs below Re = 300 suggesting a fundamental change in the character of the three-dimensional flow. At downstream distances (x/D = 10-20), the spanwise wavelength decreases from 1.42D to 1.03D as the Reynolds number increases from 300 to 1200.

Quantitative measurements of three-dimensional structures in the wake of a circular cylinder

The mechanism of flow control on a cylinder with the unsteady bleed technique

Detailed velocity measurements have been made to investigate the structure of the low‐frequency vortex dislocations that appear in the indigenous wake of a circular cylinder. It is shown that one mechanism for the production of vortex dislocations is the superposition of two waves with slightly different frequencies, where the higher frequency wave is parallel to the cylinder axis and the lower frequency is an oblique wave. In contrast to the discrete vortex concept that implies discontinuous shedding frequencies, the measured amplitude and phase distribution of the interacting waves are shown to be continuous along the span of the cylinder. Both waves (parent modes) exist simultaneously and overlap in the wake. The difference mode associated with the vortex dislocations is produced by the nonlinear interaction of the parent modes, and its maximum amplitude is at the location where the parent modes have comparable magnitude. The spanwise phase and amplitude distributions of the difference mode are ‘‘predicted’’ by taking the product of the complex wave amplitudes of the parent modes.

Oblique and parallel wave interaction in the near wake of a circular cylinder

The wave interactions which produce the low-frequency disturbances that dominate the far-wake spectrum of a circular cylinder have been studied. The spatial symmetry of interacting 2-D and 3-D waves that occur in the near wake region under natural and forced conditions are shown to follow a simple set of symmetry rules. The spanwise phase distribution of the low-frequency wave is predicted assuming a simple three-wave interaction.

Pan-Mei Yang

Papers

Quantitative measurements of three-dimensional structures in the wake of a circular cylinder

The mechanism of flow control on a cylinder with the unsteady bleed technique

Oblique and parallel wave interaction in the near wake of a circular cylinder

Symmetry of Two- and Three Dimensional Modes at a Vortex Shedding Interface in a Cylinder Wake