Unsteady Flow Distortion Past Blades: Sources of Noise Generation in Rotating Flows

Rockwell, D.; Akın, Oğuz; Kim, J. H.; Konak, S.; Kuryla, J.; Magness, C.; Robinson, Owen; Takmaz, L.; Towfighi, J.

doi:10.21236/ada255496

Cited by 3 publications

(1 citation statement)

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“…Quantitative flow visualization involved a laser-scanning version of high-imagedensity particle image velocimetry (PIV), described by Rockwell et al ( 1992, and Rockwell & Lin (1993). A scanning laser sheet was generated by steering the beam from a continuous wavelength Argon-ion laser (4 W) to a rotating mirror having 72 facets.…”

Section: Experimental System and Techniquesmentioning

confidence: 99%

Near-wake structure of an oscillating cylinder: effect of controlled shear-layer vortices

Chyu

Rockwell

1996

J. Fluid Mech.

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The instantaneous structure of the near wake of a cylinder subjected to small-amplitude perturbations is characterized using high-image-density particle image velocimetry. Emphasis is on control of the small-scale shear-layer vortices, which feed into the Kármán vortices. Modifications of the Kármán vortex formation are classified according to patterns of modulated and locked-on shear-layer vortices. The formation length of the Kármán vortices can be dramatically shortened and, in the limiting case, occur adjacent to the base of the cylinder when it is perturbed at the inherent instability frequency of the shear layer and its subharmonics. Moreover, the induced shear-layer vortices can lead to large-amplitude transverse undulations of the entire near-wake region during formation of the Kármán vortices.These variations of the near-wake structure are further elucidated by considering the transient response of the wake, induced by abrupt cessation and onset of periodic motion of the cylinder. Distinctive intermediate states of the wake arise during relaxation to its asymptotic state; such relaxation requires a very large number of periods of the inherent instability of the shear layer.

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Section: Experimental System and Techniquesmentioning

confidence: 99%

Near-wake structure of an oscillating cylinder: effect of controlled shear-layer vortices

Chyu

Rockwell

1996

J. Fluid Mech.

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High image-density particle image velocimetry using laser scanning techniques

Rockwell

Magness

Towfighi

et al. 1993

Experiments in Fluids

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Laser scanning, corresponding to time-dependent deflections of laser beam across a field of interest, can provide relatively high illumination intensity of small particles, thereby allowing implementation of high image-density particle image velocimetry (PIV). Scanning techniques employing a rotating (multi-faceted) mirror, an oscillating mirror, and an acousto-optic deflector are addressed. Issues of illumination intensity and exposure, rate of scan of the laser beam, and retrace time of the scanning beam are assessed. Representative classes of unsteady separated flows investigated with laser-scanning PIV are described.

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Kármán vortex formation from a cylinder: Role of phase-locked Kelvin–Helmholtz vortices

et al. 1995

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The formation length of Kármán vortices can be drastically reduced by small-amplitude excitation at a frequency much higher than the natural frequency of Kármán vortex formation, namely the Kelvin–Helmholtz (KH) frequency of the separating shear layer. Phase-locked patterns of KH vortices are attainable. These spatially stationary patterns coexist, however, with the spatial and temporal development of the Kármán vortices.

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Unsteady Flow Distortion Past Blades: Sources of Noise Generation in Rotating Flows

Cited by 3 publications

References 0 publications

Near-wake structure of an oscillating cylinder: effect of controlled shear-layer vortices

Near-wake structure of an oscillating cylinder: effect of controlled shear-layer vortices

High image-density particle image velocimetry using laser scanning techniques

Kármán vortex formation from a cylinder: Role of phase-locked Kelvin–Helmholtz vortices

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