Convection velocities in a turbulent boundary layer

Krogstad, Per‐Åge; Kaspersen, Jon; Rimestad, S.

doi:10.1063/1.869617

Cited by 93 publications

(98 citation statements)

References 20 publications

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“…The angle γ was measured when a streak reached the maximum inclination from the mean flow direction. The maximum angle of inclination of about 30 • detected in our visualizations compares well with an estimate given by the vector of the convection velocity U c at this height (U + c ≈ 10, as shown by Krogstad et al [25]) and the vector of the peak spanwise velocity of the Stokes layer, also at y + = 5 and for T + = 67 and W + m = 17. The maximum angle can then be estimated as follows:…”

Section: Jot 5 (2004) 024supporting

confidence: 70%

Modification of near-wall turbulence due to spanwise wall oscillations

Riccó¹

2004

J. of Turbulence

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Abstract. An experimental investigation of a turbulent boundary layer modified by spanwise wall oscillations is conducted in a water channel by means of the hydrogen-bubble technique.The purpose is to study the dynamics of near-wall turbulent structures to shed new light on the physical mechanisms characterizing the boundary layer perturbed by the wall motion and to comprehend how these changes cause a wall-shear stress reduction. It is likely that flow visualizations conducted at the highest values of maximum wall velocity describe the spatial transient evolution of the flow to the new modified state because of the limited extension of the oscillating wall section. When the oscillatory motion is imposed, the low-speed streaks shift laterally, and cyclically incline to an angle with respect to the streamwise direction. Flow visualizations from the end of the water channel distinctly show that the interaction between these low-velocity pockets and the overriding longitudinal vortices is strongly altered, the latter being only slightly disturbed by the spanwise Stokes layer which develops due to the wall movement. We also notice that the ejection phenomena of low-speed fluid from the viscous sublayer to higher regions of the boundary layer and the sweeping motions of high-speed fluid towards the wall are both significantly weakened. During the first instants of the wall oscillation, the nearwall turbulent structures are already remarkably affected after one oscillating cycle. The drag-reducing flow pattern downstream of the moving wall is also described.

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Section: Jot 5 (2004) 024supporting

confidence: 70%

Modification of near-wall turbulence due to spanwise wall oscillations

Riccó¹

2004

J. of Turbulence

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“…Kim & Hussain (1993) also found that the phase velocity of v was relatively insensitive to λ x and increased weakly with λ z , but their computational domain was too small to show the sharp growth of c for long and wide wavelengths. Krogstad, Kaspersen & Rimestad (1998) investigated a laboratory boundary layer at Re τ ≈ 600, and found an increase of the advection velocities at roughly the same values as those in figure 7.…”

Section: Dynamicsmentioning

confidence: 72%

The large-scale dynamics of near-wall turbulence

2004

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The dynamics of the sublayer and buffer regions of wall-bounded turbulent flows are analysed using autonomous numerical simulations in which the outer flow, and on some occasions specific wavelengths, are masked. The results are compared with a turbulent channel flow at moderate Reynolds number. Special emphasis is put on the largest flow scales. It is argued that in this region there are two kinds of large structures: long and narrow ones which are endogenous to the wall, in the sense of being only slightly modified by the presence or absence of an outer flow, and long and wide structures which extend to the outer flow and which are very different in the two cases. The latter carry little Reynolds stress near the wall in full simulations, and are largely absent from the autonomous ones. The former carry a large fraction of the stresses in the two cases, but are shown to be quasi-linear passive wakes of smaller structures, and they can be damped without modifying the dynamics of other spectral ranges. They can be modelled fairly accurately as being infinitely long, and it is argued that this is why good statistics are obtained in short or even in minimal simulation boxes. It is shown that this organization implies that the scaling of the near-wall streamwise fluctuations is anomalous.

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“…18 To confirm that such fluctuations of U R do not affect our study of v 2 R , we calculate their correlation…”

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confidence: 99%

Statistical mechanics and large-scale velocity fluctuations of turbulence

et al. 2011

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Turbulence exhibits significant velocity fluctuations even if the scale is much larger than the scale of the energy supply. Since any spatial correlation is negligible, these large-scale fluctuations have many degrees of freedom and are thereby analogous to thermal fluctuations studied in the statistical mechanics. By using this analogy, we describe the large-scale fluctuations of turbulence in a formalism that has the same mathematical structure as used for canonical ensembles in the statistical mechanics. The formalism yields a universal law for the energy distribution of the fluctuations, which is confirmed with experiments of a variety of turbulent flows. Thus, through the large-scale fluctuations, turbulence is related to the statistical mechanics.

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Convection velocities in a turbulent boundary layer

Cited by 93 publications

References 20 publications

Modification of near-wall turbulence due to spanwise wall oscillations

Modification of near-wall turbulence due to spanwise wall oscillations

The large-scale dynamics of near-wall turbulence

Statistical mechanics and large-scale velocity fluctuations of turbulence

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