Amplitude modulation and extreme events in turbulent channel flow

Yao, Yichen; Huang, Wei‐Xi; Xu, Chunxiao

doi:10.1007/s10409-017-0687-2

Cited by 18 publications

(13 citation statements)

References 32 publications

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“…This connection was quantitatively investigated by documenting the backflow event density beneath large-scale structures residing in the logarithmic layer. Their conclusions were confirmed in a DNS of turbulent channel flow [18] at a slightly higher Reynolds number, where a probability of finding backflow events of around 0.07% was reported at a friction Reynolds number of Re τ = 2000. In both studies a strong connection between the presence of backflow events and energetic large-scale motions in the outer region were reported.…”

Section: Introductionmentioning

confidence: 52%

“…These studies confirmed the indications in earlier works [19][20][21] regarding the presence of backflow events in wall-bounded turbulence, despite the fact that they had not been detected in certain measurement campaigns [22,23]. The more recent experimental study by Willert et al [24], who performed particle image velocimetry (PIV) measurements in zero-pressure-gradient (ZPG) turbulent boundary layers (TBLs) at Re τ = 1000 and 2700, confirmed the findings by Lenaers et al [17] and Yao, Huang, and Xu [18]. Brücker [25] used micropillar sensors to measure the topology of the wall-shear stress vector in a ZPG TBL at Re τ 940, and identified a probability of finding backflow events of around 0.05%, aligned with the results by Lenaers et al [17] at approximately the same Re.…”

Section: Introductionmentioning

confidence: 56%

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Backflow events under the effect of secondary flow of Prandtl's first kind

et al. 2020

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A study of the backflow events in the flow through a toroidal pipe at friction Reynolds number Re τ ≈ 650 is performed and compared with the results in a straight turbulent pipe flow at Re τ ≈ 500. The statistics and topological properties of the backflow events are analysed and discussed. Conditionally averaged flow fields in the vicinity of the backflow event are obtained, and the results for the torus show a similar streamwise wall-shear stress topology which varies considerably for the azimuthal wall-shear stress when compared to the pipe flow. In the region around the backflow events, critical points are observed. The comparison between the toroidal pipe and its straight counterpart also shows fewer backflow events and critical points in the torus. This is attributed to the secondary flow of Prandtl's first kind present in the toroidal pipe, which is responsible for the convection of momentum from the inner to the outer bend through the core of the pipe, and back from outer bend to the inner bend along the azimuthal direction. These results indicate that backflow events and critical points are genuine features of wall-bounded turbulence, and are not artefacts of specific boundary or inflow conditions in simulations and/or measurement uncertainties in experiments.

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Section: Introductionmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 56%

Backflow events under the effect of secondary flow of Prandtl's first kind

et al. 2020

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“…Mathis et al 2009;Harun et al 2013;Squire et al 2016a;Yao et al 2018, for instance). The fluctuating flow is hence split into large-scale dynamics u and small-scale fluctuations u using a low-pass gate function g(t) of cutoff frequency f co , u = u + u , u = g * u, u = u − u.…”

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confidence: 99%

Spatial modulations of kinetic energy in the roughness sublayer

2018

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High-Reynolds-number experiments are conducted in the roughness sublayer of a turbulent boundary layer developing over a cubical canopy. Stereoscopic particle image velocimetry is performed in a wall-parallel plane to evidence a high degree of spatial modulation of the small-scale turbulence around the footprint of large-scale motions, despite the suppression of the inner layer by the high roughness elements. Both Fourier and wavelets analyses show that the near-wall cycle observed in smooth-wall-bounded flows is severely disrupted by the canopy, whose wake in the roughness sublayer generates a new range of scales, closer to that of the outer-layer large-scale motions. This restricts significantly scale separation, hence a diagnostic method is developed to divide carefully and rationally the fluctuating velocity fields into large- and small-scale components. Our analysis across all turbulent kinetic energy terms sheds light on the spatial imprint of the modulation mechanism, revealing a very different signature on each velocity component. The roughness sublayer shows a preferential arrangement of the modulated scales similar to what is observed in the outer layer of smooth-wall-bounded flows – small-scale turbulence is enhanced near the front of high momentum regions and damped at the front of low momentum regions. More importantly, accessing spanwise correlations reveals that modulation intensifies the most along the flanks of the large-scale motions.

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“…in Chung & McKeon (2010) (see figure 4 therein) for the streamwise velocity, , or in Yao et al. (2018) (see figure 3( c ) therein) for the and components. However, to the best of our knowledge, this peculiar increase of the modulation parameter in the channel flow has not been explicitly discussed so far.…”

Section: Resultsmentioning

confidence: 98%

“…see Chung & McKeon 2010; Bernardini & Pirozzoli 2011; Agostini & Leschziner 2014; Agostini, Leschziner & Gaitonde 2016; Anderson 2016; Hwang et al. 2016; Yao, Huang & Xu 2018; Agostini & Leschziner 2019; Dogan et al. 2019).…”

Section: Introductionmentioning

confidence: 99%