Low-Frequency Modulations Associated with Vortex Shedding due to Flow over a Bluff Body

Miau, Jiun‐Jih; Wu, S. J.; Hu, Cheng Chao; Chou, Jung-Hua

doi:10.2514/6.2003-1122

Cited by 2 publications

(5 citation statements)

References 31 publications

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“…The images in figure 3(c) show the unsteady appearance of the separated shear layer in the near-wake region from a side view, which are reproduced from Miau et al (2004). An interesting feature revealed is that the size of the vortex formation region is varying with time, seen from a comparison of the images corresponding to the time periods I and II.…”

Section: Resultsmentioning

confidence: 76%

“…Referring to the raw hot-wire signals, included for reference, one sees that the fluctuating amplitude of the velocity signals within period I appears to be substantially larger than that within period II. For a quantitative investigation of the relation between the instantaneous characteristics of the velocity signals and the unsteadiness of the vortex formation region, refer to Miau et al (2004).…”

Section: Resultsmentioning

confidence: 99%

“…Recently, the present authors (Miau et al 2004) have made an attempt, employing a wavelet transformation, to obtain the vortex shedding frequency from the hot-wire signals measured in the near-wake region behind a normal plate. This analysis showed that the instantaneous vortex shedding frequencies obtained were in good correlation with the low-frequency modulations in the signals.…”

Section: Introductionmentioning

confidence: 99%

“…Based on the previous findings (Miau et al 2003(Miau et al , 2004, the present work is aimed at examining the vortex shedding characteristics at different spanwise locations, in order to gain a better understanding of the unsteady, three-dimensional behaviour of flow in the near-wake region. Of particular interest are the instantaneous characteristics of vortex shedding along the spanwise direction, based on the quantities obtained by a wavelet analysis.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

On low-frequency modulations and three-dimensionality in vortex shedding behind a normal plate

Miau

et al. 2005

J. Fluid Mech.

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In this study spanwise correlation measurements and smoke flow visualization were performed on vortex shedding behind a normal plate. For Reynolds numbers in a range between 1800 and 27 000, the hot-wire signals measured were analysed by a wavelet transformation, from which the instantaneous properties of vortex shedding were obtained and examined. Results show that the phase difference of vortex shedding detected at two spanwise locations, separated by twice the characteristic length, can be as high as 35 •. A correlation analysis further shows that large spanwise phase differences occur when small fluctuating amplitudes in the vortex shedding signals are measured. Smoke-wire visualization performed at Reynolds number 1800 indicates that the formation of shedding vortex can be divided into two distinct situations, namely, one featuring a long formation region, called Mode L; and the other featuring a short formation region, called Mode S. In Mode S, the three-dimensionality of vortex formation appears to be very pronounced, and the secondary vortices are clearly present in the separated shear layer. The events of Mode S occupy less than 5% of the total time measured, and are called the burst events in this study.

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Section: Resultsmentioning

confidence: 76%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On low-frequency modulations and three-dimensionality in vortex shedding behind a normal plate

Miau

et al. 2005

J. Fluid Mech.

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“…Except for low Re d , below the appearance of threedimensional instabilities, disruptions or modifications of the shedding process are inherent to wakes for twodimensional circular cylinders (Tritton 1959;Williamson 1992), normal flat plates (Najjar and Balachander 1998;Miau et al 2004;Wu et al 2005) and square cylinders (Bearman and Obasaju 1982;Bailey et al 2002). For these geometries, events of disruption in the von Kármán shedding process are associated with local dislocation/split in vortex tubes.…”

Section: Introductionmentioning

confidence: 95%

On the vortex dynamics in the wake of a finite surface-mounted square cylinder

2011

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The shedding process in the near wake of a surface-mounted, square cross-section cylinder of heightto-width aspect ratio 4 at a Reynolds number of 12,000 based on free-stream velocity and the obstacle width was investigated. The boundary layer thickness was 0.18 obstacle heights based on 99% free-stream velocity. The study is performed using planar high frame-rate particle image velocimetry synchronized with pressure measurements and hot-wire anemometry. Spatial cross-correlation, instantaneous phase relationships, and phase-averaged velocity data are reported. Two dominant vortex-shedding regimes are observed. During intervals of high-amplitude pressure fluctuations on the obstacle side faces, alternate formation and shedding of vortices is observed (regime A) similar to the von Kármán process. Regime B is characterized by two co-existing vortices in the obstacle lee throughout the shedding cycle and is observed within lowamplitude pressure fluctuation intervals. Despite the coexisting vortices in the base region, opposite sign vorticity is still shed out-of-phase downstream of this vortex pair giving rise to a staggered arrangement of counterrotating vortices downstream. While the probability of occurrence of Regime B increases toward the free end, the amplitude modulation remains coherent along the obstacle height. Conditionally phase-averaged reconstructions of the flow field are consistent with the spatial distribution of the phase relationships and their probability density function. Earlier observations are reconciled showing that the symmetric shedding of vortices is a rare occurrence.

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Low-Frequency Modulations Associated with Vortex Shedding due to Flow over a Bluff Body

Cited by 2 publications

References 31 publications

On low-frequency modulations and three-dimensionality in vortex shedding behind a normal plate

On low-frequency modulations and three-dimensionality in vortex shedding behind a normal plate

On the vortex dynamics in the wake of a finite surface-mounted square cylinder

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