Nonequilibrium state in energy spectra and transfer with implications for topological transitions and SGS modeling

Horiuti, Kiyosi; Yanagihara, Shinya; Tamaki, Takahiro

doi:10.1088/0169-5983/48/2/021409

Cited by 5 publications

(3 citation statements)

References 18 publications

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“…One such model can be derived by expanding about a base Kolmogorov − 5 3 spectrum to obtain additional components that correspond to fluctuations in dissipation [79] that may be a consequence of macroscale coupling. An alternative, and more empirical, but more direct velocity-intermittency framework would be to use the Hölder exponent as a means to scale velocity fluctuations and develop fractal-based closures [80,81] into a multifractal formulation where the velocity field guides the value of the selected Hölder exponent.…”

Section: Discussionmentioning

confidence: 99%

Large eddy simulation of the velocity-intermittency structure for flow over a field of symmetric dunes

2016

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Owing to their frequent occurrence in the natural environment, there has been significant interest in refining our understanding of flow over dunes and other bedforms. Recent work in this area has focused, in particular, on their shear layer characteristics and the manner by which flow structures are generated. However, field-based studies, are reliant on single-, or multi-point measurements, rather than delimiting flow structures from the velocity gradient tensor as is possible in numerical work. Here, we extract pointwise time series from a well-resolved large-eddy simulation as a means to connect these two approaches. The at-a-point analysis technique is termed the velocityintermittency quadrant method and relates the fluctuating, longitudinal velocity, u ′ 1 (t), to its fluctuating pointwise Hölder regularity, α ′ 1 (t).Despite the difference in boundary conditions, our results agree very well with previous experiments that show the importance, in the region above the dunes, of a quadrant 3 (uflow configuration. Our higher density of sampling beneath the shear layer and close to the bedforms relative to past experimental work reveals a negative correlation between u ′ 1 (t) and α

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Section: Discussionmentioning

confidence: 99%

Large eddy simulation of the velocity-intermittency structure for flow over a field of symmetric dunes

2016

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“…flat sheets). Dissipation is known to arise preferentially in the curved sheets that wrap around vortex tubes [Kerr, 1985, Jimenez et al, 1993, Kawahara, 2005, Horiuti et al, 2016 and a high degree of normal straining is particularly prevalent along the Vieillefosse tail between regions 5 and 6 [Keylock, 2018]. Hence, the region 5 = 1 occurrences have a topology that favours dissipation relative to the = 0 cases in this region.…”

Section: The Location and Orientation Of Coherent Regions Where =mentioning

confidence: 99%

Turbulence at the Lee bound: maximally non-normal vortex filaments and the decay of a local dissipation rate

Keylock¹

2019

J. Fluid Mech.

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This paper uses a tight mathematical bound on the degree of the non-normality of the turbulent velocity gradient tensor to classify flow behaviour within vortical regions (where the eigenvalues of the tensor contain a conjugate pair). Structures attaining this bound are preferentially generated where enstrophy exceeds total strain and there is a positive balance between strain production and enstrophy production. Lagrangian analysis of homogeneous, isotropic turbulence shows that attainment of this bound is associated with relatively short durations and an upper limit to the spatial extent of the flow structures that is similar to the Taylor scale. An analysis of the dynamically relevant terms using a recently developed formulation (Keylock, J. Fluid Mech., vol. 848, 2018, pp. 876–904), highlights the controls on this dynamics. In particular, in high enstrophy regions it is shown that the bound is attained when normal strain decreases rather than when non-normality increases. The near absence of normal total strain results in a source of intermittency in the dynamics of dissipation that is hidden in standard analyses. It is shown that of the two terms that contribute to the non-normal production dynamics, it is the one that is typically smallest in magnitude that is of greatest importance within these $\ell =1$ filaments. The typical distance between filament centroids is just less than a Taylor scale, implying a connection to the manner in which flow topology at the Taylor scale explains dissipation at smaller scales.

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“…Wang et al's use of LES and adoption of vortex sheet identification methods developed by Horiuti and Takagi (2005), leads to a clear connection to the final paper in the special issue. This is by Horiuti et al (2016) and integrates a consideration of many of the aspects of turbulence dynamics considered by the other authors, including dissipation, non-equilibrium dynamics, vortex topology and helicity. A perturbation expansion of Kolmogorov's −5/3 law reveals additional components as a consequence of fluctuations in the dissipation rate that imply an absence of a simple equilibrium between production and dissipation.…”

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confidence: 99%

JSPS Supported Symposium on Interscale Transfers and Flow Topology in Equilibrium and Non-equilibrium Turbulence (Sheffield, UK, September 2014)

2016

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This collection of papers is a selection of the work presented at the symposium on Interscale Transfers and Flow Topology in Equilibrium and Non-Equilibrium Turbulence, held at the Department of Civil and Structural Engineering, University of Sheffield, on the 15th and 16th of September, 2014. The meeting was kindly supported by the generosity of the Japan Society for the Promotion of Science (JSPS) in London and Professor Kunio Takeyasu, the Director of JSPS London, came to Sheffield to deliver an enthusiastic welcome address to the attendees, who had travelled from universities in Japan, the UK, France, and Germany.Whilst the papers in this collection span the breadth of work presented, and in some cases are a result of collaborations initiated at that meeting, any reflection on the success of the symposium is tainted by the sadness that we all felt following the death of Norbert Peters in July 2015. Norbert's contributions to both turbulence and combustion were immense and his novel approaches to conceptualising turbulence phenomena will long be of use to the community. Norbert enthusiastically participated in all aspects of the Sheffield meeting, from the proposal writing stage through to acting as a Guest Editor for this special issue. Consequently, it is only befitting that the first paper in this volume is an appreciation of Norbert as scientist and human being, written by his long-term collaborator, Heinz Pitsch.The title for the symposium was suggested by Christos Vassilicos who, along with Norbert, also undertook a great deal of work behind the scenes to help this meeting take place. It refers to some of the theoretical and practical complexities that result from studying turbulence dissipation and the manner by which energy, helicity and other quantities move from large to small scales when production and dissipation are not necessarily in balance locally. Even in the classical case of the study of energy transfers in equilibrium, there are ongoing uncertainties regarding a description of the pertinent mechanisms, whether this is regarding intermittency corrections to structure function scaling laws, or the topology of vortex interaction in the transfer process. Add to this a solid boundary, as arises in most industrial or environmental applications, and the departure from isotropy causes further complications. Force a flow at multiple scales (as arises in canopy flows in nature, for example) rather than a single large scale and there will be further difficulties in applying classical theory. Because an understanding of such matters is of importance in a variety of industrial and environmental situations, a future generation of numerical models will be predicated on this more nuanced physics if they are to model turbulence dissipation and production correctly.The presentation at the meeting by Christos Vassilicos on the nature of dissipation set the scene in this regard, and his major review of recent progress in this area was published soon after the meeting (Vassilicos 2015). From a more applied pers...

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Nonequilibrium state in energy spectra and transfer with implications for topological transitions and SGS modeling

Cited by 5 publications

References 18 publications

Large eddy simulation of the velocity-intermittency structure for flow over a field of symmetric dunes

Large eddy simulation of the velocity-intermittency structure for flow over a field of symmetric dunes

Turbulence at the Lee bound: maximally non-normal vortex filaments and the decay of a local dissipation rate

JSPS Supported Symposium on Interscale Transfers and Flow Topology in Equilibrium and Non-equilibrium Turbulence (Sheffield, UK, September 2014)

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