Characterization of coherent vortical structures in a supersonic turbulent boundary layer

Pirozzoli, Sergio; Bernardini, Matteo; Grasso, Francesco

doi:10.1017/s0022112008003005

Cited by 141 publications

(160 citation statements)

References 42 publications

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“…The inner dimension of vortex clusters in figure 6(d) is r 1 ≈ 6η, independently of the cluster volume, which approximately agrees with the diameter of individual filamentary vortices in turbulence (Jiménez & Wray 1998;Tanahashi, Iwase & Miyauchi 2001;del Álamo et al 2006;Pirozzoli, Bernardini & Grasso 2008;Stanislas, Perret & Foucaut 2008). It is also consistent with the description of vortex clusters as 'sponges of strings' (LFJ12).…”

Section: Flow Anisotropysupporting

confidence: 82%

Coherent structures in statistically stationary homogeneous shear turbulence

et al. 2017

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The three-dimensional vortex clusters, and the structures based on the quadrant classification of the intense tangential Reynolds stress (Qs), are studied in direct numerical simulations of statistically stationary homogeneous shear turbulence (HST) at Taylor microscale Reynolds number Re λ ≈ 50-250, with emphasis on comparisons with turbulent channels (CHs). The Qs and vortex clusters in HST are found to be versions of the corresponding detached (in the sense of del Álamo et al. (J. Fluid Mech., vol. 561 (2006), pp. 329-358)) structures in CHs, although statistically symmetrised with respect to the substitution of sweeps by ejections and vice versa. In turn, these are more symmetric versions of the corresponding attached Qs and clusters. In both flows, only co-gradient sweeps and ejections larger than the local Corrsin scale are found to couple with the shear. They are oriented anisotropically, and are responsible for carrying most of the total Reynolds stress. Most large eddies in CHs are attached to the wall, but it is shown that this is probably a geometric consequence of their size, rather than the reason for their dynamical significance. Most small Q structures associated with different quadrants are far from each other in comparison to their size, but those that are close to each other tend to form quasi-streamwise trains of groups of a sweep and an ejection paired side by side in the spanwise direction, with a vortex cluster in between, generalising to three dimensions the corresponding arrangement of attached eddies in CHs. These pairs are organised around an inclined large-scale conditional vortex 'roller', and it is shown that the composite structure tends to be located at the interface between high-and low-velocity streaks, as well as in strong 'co-gradient' shear layers that separate streaks of either sign in which velocity is more uniform. It is further found that the conditional rollers are terminated by 'hooks' reminiscent of hairpins, both upright and inverted. The inverted hook weakens as the structures approach the wall, while the upright one changes little. At the same time, the inclination of the roller with respect to the mean velocity decreases from 45 • in HST to quasi-streamwise for † Email address for correspondence: jimenez@torroja.

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Section: Flow Anisotropysupporting

confidence: 82%

Coherent structures in statistically stationary homogeneous shear turbulence

et al. 2017

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“…The average convection velocity of similar structures in a boundary layer and channel flow has already received considerable attention in the literature (e.g. Kim & Hussain 1993;Krogstad et al 1998;Pirozzoli et al 2008;Del Alamo & Jimenez 2009), and the tracking results just lend additional support for the earlier observations. The average convection velocity inferred from the tracks is constant over the considered time period and equal to 0.78U e ± 0.004U e in the streamwise direction (equal to the local mean flow velocity at a distance of 0.2δ from the wall), 0.006U e ± 0.002U e in the wall-normal direction and zero in the spanwise direction (±0.003U e ).…”

Section: Dispersion Of Vortices 41 Convection Of Individual Vorticessupporting

confidence: 64%

“…The width of these p.d.f.s decreases with increasing wall-normal distance similar to the turbulence intensity. Pirozzoli, Bernardini & Grasso (2008) performed a similar analysis in a supersonic boundary layer, but reported only the average convection velocity in the streamwise and wall-normal direction.…”

Section: Introductionmentioning

confidence: 99%

Tracking of vortices in a turbulent boundary layer

et al. 2012

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The motion of spanwise vortical elements and large-scale bulges has been tracked in the outer region between wall-normal distance z/δ = 0.11 and 0.30 of a turbulent boundary layer at Re θ = 2460. The experimental dataset of time-resolved threedimensional velocity fields used has been obtained by tomographic particle image velocimetry. The tracking of these structures yields their respective average trajectories as well as the variations thereof, quantified by the root mean square of the trajectory coordinates as a function of time. It is demonstrated that the variation in convection can be described by a dispersion model for infinitesimal particles in homogeneous turbulence, which suggests that these vortical structures and bulges are transported passively by the external velocity field without significant changes in their topology, at least over the present observation time of 1.2δ/U e . However, this does not mean that the structure's convection velocity is equal to the local flow velocity at each instant. Differences of the order of the Kolmogorov or wall friction velocity have been observed for the spanwise vortical elements. In addition, the simultaneous detection and tracking of multiple structures allows an evaluation of the relative velocity between two spanwise vortex elements, which are approximately aligned along the streamwise direction. The typical streamwise distance between such neighbouring structures is found to be around 0.2δ. Their relative velocities are small, especially the streamwise component, which shows less variation as may be expected based on the relative flow velocity statistics for the same separation distance. This appears consistent with the hairpin packet model, which comprises a set of streamwise aligned hairpins travelling coherently. In exceptional cases, however, the structures approach each other rapidly, forcing an interaction on a time scale of the order of 1δ/U e . It is shown that the measured variation in convection velocity can further be used successfully to predict the temporal development of space-time correlation functions starting from the instantaneous correlation map. In this prediction the structures are assumed to convect without change, following our observations.

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“…The simulation was initiated by superposing organized disturbances mimicking streaks and ejection/sweep events onto a standard mean turbulent boundary layer profile, to achieve fast transition to a turbulent state. 21 The simulation was initially run for about T 0 ≈ 10δ/u τ eddy turnover times, 14 until stationarity was observed for the boundary layer shape factor, which is in our experience a sensitive indicator. Statistics were then collected by averaging in time over an interval T ≈ 4δ/u τ , in the spanwise direction, and also in the streamwise direction, in slabs about one local boundary layer thickness wide.…”

mentioning

confidence: 99%

Probing high-Reynolds-number effects in numerical boundary layers

Pirozzoli

Bernardini

2013

Physics of Fluids

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We study the high-Reynolds-number behavior of a turbulent boundary layer in the low supersonic regime through very-large-scale direct numerical simulation (DNS). For the first time a Reynolds number is attained in DNS (Re-tau = delta/delta(v) approximate to 4000, where delta is the boundary layer thickness and delta(v) is the viscous length scale) at which theoretical predictions and experiments suggest the occurrence of phenomena pertaining to the asymptotic Reynolds number regime. From comparison with previous DNS data at lower Reynolds number we find evidence of a continuing trend toward a stronger imprint of the outer-layer structures onto the near-wall region. This effect is clearly manifested both in flow visualizations, and in energy spectra. More than a decade of nearly-logarithmic variation is observed in the mean velocity profiles, with log-law constants k approximate to 0.394, C approximate to 4.84, and a trend similar to experiments. We find some supporting evidence for the debated existence of a k(-1) region in the power spectrum of streamwise velocity fluctuations, which extends up to y(+) approximate to 150, and of a k(-5/3) spectral range in the outer layer. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792164

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Characterization of coherent vortical structures in a supersonic turbulent boundary layer

Cited by 141 publications

References 42 publications

Coherent structures in statistically stationary homogeneous shear turbulence

Coherent structures in statistically stationary homogeneous shear turbulence

Tracking of vortices in a turbulent boundary layer

Probing high-Reynolds-number effects in numerical boundary layers

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