Bursting and critical layer frequencies in minimal turbulent dynamics and connections to exact coherent states

Park, Jae Sung; Shekar, Ashwin; Graham, Michael D.

doi:10.1103/physrevfluids.3.014611

Cited by 18 publications

(20 citation statements)

References 68 publications

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“…Indeed, the critical transition to a turbulent state has exponents comparable to those of directed percolation, concerning, for example, the scaling of the number of active sites in terms of distance to the critical governing parameter of the transition. Such an analysis also shows the importance of large‐scale zonal flows (Shih et al, ) of critical layers (Park et al, ), as well as that of regeneration self‐sustaining cycles in such flows (Kawahara & Kida, ; Waleffe, ) with, citing Mckeon (), “the importance of scale interactions in sustaining wall turbulence through the nonlinear term.”…”

Section: The Bidirectional or Dual Cascades In Turbulencementioning

confidence: 97%

Helicity Dynamics, Inverse, and Bidirectional Cascades in Fluid and Magnetohydrodynamic Turbulence: A Brief Review

Pouquet

Rosenberg

Stawarz

et al. 2019

Earth and Space Science

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We briefly review helicity dynamics, inverse and bidirectional cascades in fluid and magnetohydrodynamic (MHD) turbulence, with an emphasis on the latter. The energy of a turbulent system, an invariant in the nondissipative case, is transferred to small scales through nonlinear mode coupling. Fifty years ago, it was realized that, for a two‐dimensional fluid, energy cascades instead to larger scales and so does magnetic excitation in MHD. However, evidence obtained recently indicates that, in fact, for a range of governing parameters, there are systems for which their ideal invariants can be transferred, with constant fluxes, to both the large scales and the small scales, as for MHD or rotating stratified flows, in the latter case including quasi‐geostrophic forcing. Such bidirectional, split, cascades directly affect the rate at which mixing and dissipation occur in these flows in which nonlinear eddies interact with fast waves with anisotropic dispersion laws, due, for example, to imposed rotation, stratification, or uniform magnetic fields. The directions of cascades can be obtained in some cases through the use of phenomenological arguments, one of which we derive here following classical lines in the case of the inverse magnetic helicity cascade in electron MHD. With more highly resolved data sets stemming from large laboratory experiments, high‐performance computing, and in situ satellite observations, machine learning tools are bringing novel perspectives to turbulence research. Such algorithms help devise new explicit subgrid‐scale parameterizations, which in turn may lead to enhanced physical insight, including in the future in the case of these new bidirectional cascades.

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Section: The Bidirectional or Dual Cascades In Turbulencementioning

confidence: 97%

Helicity Dynamics, Inverse, and Bidirectional Cascades in Fluid and Magnetohydrodynamic Turbulence: A Brief Review

Pouquet

Rosenberg

Stawarz

et al. 2019

Earth and Space Science

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“…Thus, these spikes or dips cannot be used to identify the onset/footprint of low- or high-drag events. Park et al [ 16 ], using MFU simulations, observed that many of the low-drag events are followed by strong turbulent bursts which were detected based on an increase in the volume-averaged energy dissipation rate. There may exist a relation between these turbulent bursts and spikes in the ensemble-averaged wall shear stress data after low-drag events which needs further investigation.…”

Section: Wall Shear Stress Statistics During Conditional Eventsmentioning

confidence: 99%

“…They observed that the bursting process is linked to the instability of the TW solution. Park et al [ 16 ] studied the connection between the bursting process and the ECS solutions in minimal channel flow for

. They focussed on the P4 family of ECS solutions, as identified earlier by Park and Graham [ 13 ].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, Pereira et al [ 25 ] carried out DNS in channel flow of domain size,

between 69.26 and 180 for Newtonian flow, and at

= 180 for drag-reducing flow (65% drag reduction). The flow was identified as hibernating if the spatially-averaged wall shear stress was lower than

of its time-averaged value and no time criteria were used (unlike previous studies where a minimum time duration was also used to detect a hibernating event, for example, in [ 16 , 22 , 24 ]). They demonstrated that the transition to turbulence in Newtonian flows shares various common features to the polymer induced drag reduction in turbulent flows.…”

Section: Introductionmentioning

confidence: 99%

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Low- and High-Drag Intermittencies in Turbulent Channel Flows

Agrawal

Davis

et al. 2020

Entropy

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Recent direct numerical simulations (DNS) and experiments in turbulent channel flow have found intermittent low- and high-drag events in Newtonian fluid flows, at Reτ=uτh/ν between 70 and 100, where uτ, h and ν are the friction velocity, channel half-height and kinematic viscosity, respectively. These intervals of low-drag and high-drag have been termed “hibernating” and “hyperactive”, respectively, and in this paper, a further investigation of these intermittent events is conducted using experimental and numerical techniques. For experiments, simultaneous measurements of wall shear stress and velocity are carried out in a channel flow facility using hot-film anemometry (HFA) and laser Doppler velocimetry (LDV), respectively, for Reτ between 70 and 250. For numerical simulations, DNS of a channel flow is performed in an extended domain at Reτ = 70 and 85. These intermittent events are selected by carrying out conditional sampling of the wall shear stress data based on a combined threshold magnitude and time-duration criteria. The use of three different scalings (so-called outer, inner and mixed) for the time-duration criterion for the conditional events is explored. It is found that if the time-duration criterion is kept constant in inner units, the frequency of occurrence of these conditional events remain insensitive to Reynolds number. There exists an exponential distribution of frequency of occurrence of the conditional events with respect to their duration, implying a potentially memoryless process. An explanation for the presence of a spike (or dip) in the ensemble-averaged wall shear stress data before and after the low-drag (or high-drag) events is investigated. During the low-drag events, the conditionally-averaged streamwise velocities get closer to Virk’s maximum drag reduction (MDR) asymptote, near the wall, for all Reynolds numbers studied. Reynolds shear stress (RSS) characteristics during these conditional events are investigated for Reτ = 70 and 85. Except very close to the wall, the conditionally-averaged RSS is higher than the time-averaged value during the low-drag events.

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“…In more current understanding, however, buffer-layer 'bursting' is believed to be associated with quasi-periodic breakdown of unstable coherent structures presumably described by travelling wave solutions of Navier-Stokes equations (Jiménez (2013), sections IV.A-B; Park, Shekar & Graham 2018). The quasi-period of this bursting is expected to be 400 viscous times t ν = ν/u 2 * with duration 100 viscous times, during which the travelling structure evolves from a low wall stress to high wall stress state; see, for example, Jiménez (2013), figure 10, or Park et al (2018), figure 6. Therefore, 'ejections' and 'sweeps' in our sense may both be associated with buffer-layer bursting, at different stages in the evolution of the burst.…”

Section: Identification Of Ejections and Sweepsmentioning

confidence: 99%

Stochastic Lagrangian dynamics of vorticity. Part 2. Application to near-wall channel-flow turbulence

2020

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Bursting and critical layer frequencies in minimal turbulent dynamics and connections to exact coherent states

Cited by 18 publications

References 68 publications

Helicity Dynamics, Inverse, and Bidirectional Cascades in Fluid and Magnetohydrodynamic Turbulence: A Brief Review

Helicity Dynamics, Inverse, and Bidirectional Cascades in Fluid and Magnetohydrodynamic Turbulence: A Brief Review

Low- and High-Drag Intermittencies in Turbulent Channel Flows

Stochastic Lagrangian dynamics of vorticity. Part 2. Application to near-wall channel-flow turbulence

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