An experimental investigation of the wake structure behind a disk

Lee, S.J.; Bearman, P. W.

doi:10.1016/0889-9746(92)90025-x

Cited by 20 publications

(10 citation statements)

References 8 publications

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“…The dominant peak corresponding to large-scale vortex shedding is detected at all the probes, while the broadband peak related to the shear-layer instability is only clearly identified at the probes located in the separated shear layer. The main frequencies corresponding to large-scale vortex shedding ( f vs ) and the shear-layer instability ( f KH ) at Re = 3000 and 10 4 are in good agreement with the results by Lee and Bearman 48 In addition to the large-scale vortex shedding frequency and the high frequency corresponding to the shear-layer instability, some peaks at much lower frequencies have also been observed in the cases of Re ≥ 300. As shown in Figure 5(b), at Re = 300, the frequency spectrum at P1 in the separated shear layer also exhibits a peak at a much lower frequency of f p ≈ 0.03.…”

Section: B Frequency Analysissupporting

confidence: 84%

Low-frequency characteristics in the wake of a circular disk

Yang

Liu

et al. 2015

Physics of Fluids

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Numerical simulations of flow over a circular disk have been performed in this study at Re = 250, 300, 3000, and 104. The Fourier spectra analysis of the velocity at different positions suggests that together with the natural vortex-shedding frequency and the shear-layer Kelvin-Helmholtz instability frequency, several much lower frequencies are also detected when the Reynolds number (Re) increases to 300: one is fp ≈ 0.03, another one is fr ≈ 0.02, and its second harmonic is at about 0.04 and a low frequency of about 0.05. Considering the limited time length of the data, time-frequency analysis based on wavelet transform is then performed. It is found that the local frequencies of the amplitude peaks for the large-scale vortex shedding and shear-layer Kelvin-Helmholtz instability vary irregularly with time, indicating that the traditional Fourier analysis of the numerical signals would not be representative. Nevertheless, the low frequencies fp ≈ 0.03 and fr ≈ 0.02 are clearly confirmed. The frequencies of about 0.04 and 0.05 are observed to occur in some time periods but with much weaker magnitude. It is found that the low-frequency signals keep nearly invariant as Reynolds number increases. The physical origins of the low frequencies fp ≈ 0.03 and fr ≈ 0.02 are then investigated. The physical origin of fp ≈ 0.03 is due to a low-frequency pumping motion of the recirculation bubble, and the fr ≈ 0.02 signal is due to a low-frequency modulation in the rotation of the azimuthal location of large-scale vortex shedding (i.e., the changing of the rotation direction). To characterize the low-frequency unsteadiness of the recirculation bubble, the temporal evolution of the low-pass filtered flow field is investigated. It is observed that the pumping motion of the recirculation bubble is associated with the growing and shedding of the large toroidal vortices formed in the bubble, which is closely related to the behavior of the separated shear layer. The separated shear layer rolls up later in the state with longer recirculation bubble, whereas it rolls up earlier in the state with shorter bubble.

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Section: B Frequency Analysissupporting

confidence: 84%

Low-frequency characteristics in the wake of a circular disk

Yang

Liu

et al. 2015

Physics of Fluids

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“…IV, we investigate the structure of the wake using Fourier decomposition on two-point measurements, similar to those done in the wake of a disk and other axisymmetric bodies. [6][7][8]10,11 …”

Section: The Structure Of the Turbulent Wakementioning

confidence: 98%

“…Johansson and George 5 provide an extensive review of the various qualitative and quantitative studies that have investigated the structure of turbulent axisymmetric wakes. Of particular interest in the context of this study are the works by Roberts, 6 Fuchs et al, 7 Berger et al, 8 Cannon, 9 Lee and Bearman, 10 Cannon et al, 11 and Johansson et al 12 This body of work investigated the large-scale coherent structures in axisymmetric wakes through means of cross-correlations of multiple points in space. By decomposing these signals, either through azimuthal Fourier decomposition or proper orthogonal decomposition (POD), it was possible to determine the most energetic modes within the wake.…”

Section: Introductionmentioning

confidence: 98%

Geometrical influence on vortex shedding in turbulent axisymmetric wakes

et al. 2015

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We investigate the structures generated by the vortex shedding mechanism in turbulent axisymmetric wakes of non-axisymmetric plates, including a square plate and a series of fractal plates, and compare the results to a disk. For a given characteristic length ℓ, all plates have the same frontal area A, since ℓ = A 0.5 , but the length of the perimeter and the irregularity of the perimeter were varied in a fractal manner thus allowing us to investigate the effect of boundary conditions. Measurements were taken over a large range of downstream and radial distances in order to obtain a more robust measure for the vortex shedding energy. It was found that the fractal plates are able to reduce the vortex shedding energy by as much as 60% compared to the disk and square plates. It was also found that the frequency at which the vortex shedding structures are generated and the manner in which they organise themselves in the wake are independent of the boundary conditions of the wake generator. The results suggest that the main function of the multi-scale segments around the perimeter of the plates is to re-distribute the energy to a broader range of scales in the flow, which could explain the previously observed increase in drag coefficient for the fractal edged plates. C 2015 AIP Publishing LLC. [http://dx.

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“…The large-scale, 'coherent' features of this flow have not only been studied using flow visualization, but also by means of phase averaging and conditional sampling techniques (Lee & Bearman 1992;Miau et al 1997;Perry & Lim 1978;Perry & Watmuff 1981). Most interestingly in the context of this paper, Roberts (1973), and later Fuchs, Mercker & Michel (1979) used two hot wires to measure cross-spectra at a single radius of the near wake.…”

Section: Introductionmentioning

confidence: 99%

The far downstream evolution of the high-Reynolds-number axisymmetric wake behind a disk. Part 2. Slice proper orthogonal decomposition

Johansson

George

2006

J. Fluid Mech.

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The high-Reynolds-number axisymmetric wake behind a disk has been studied from x/D = 30 to x/D = 150 using the proper orthogonal decomposition (POD) applied to measurements of the streamwise fluctuating velocity. It was found that the energetic structure of the axisymmetric wake can very efficiently be described in terms of POD modes. The first radial (or lowest-order) POD mode has 56 % of the energy. Two major features dominate the eigenspectra, manifested as two major peaks. The first peak is an azimuthal mode-1 peak at a frequency corresponding to the Strouhal number of the near wake. The second is an azimuthal mode-2 peak at near-zero frequency. The mode-1 peak dies out faster than the mode-2 peak, so that the far wake is dominated by the latter. This evolution from azimuthal mode-1 dominance in the near wake to mode-2 dominance in the far wake corresponds closely to the approach to equilibrium similarity. Once azimuthal mode-2 becomes equally important as azimuthal mode-1 (after x/D = 30 or x/θ = 110), the ratio of turbulence intensity to centreline velocity deficit is constant, the mean deficit and turbulence intensity collapse in similarity variables, and the wake grows as x 1/3 .

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An experimental investigation of the wake structure behind a disk

Cited by 20 publications

References 8 publications

Low-frequency characteristics in the wake of a circular disk

Low-frequency characteristics in the wake of a circular disk

Geometrical influence on vortex shedding in turbulent axisymmetric wakes

The far downstream evolution of the high-Reynolds-number axisymmetric wake behind a disk. Part 2. Slice proper orthogonal decomposition

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