Turbulence structure and turbulence kinetic energy transport in multiscale/fractal-generated turbulence

Nagata, Kouji; Sakai, Yasuhiko; Inaba, Takehiko; Suzuki, Hiroki; Terashima, Osamu; Suzuki, Hiroyuki

doi:10.1063/1.4811402

Cited by 95 publications

(92 citation statements)

References 16 publications

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“…In effect, the turbulence generated by the fractal grid is distributed along the longitudinal direction, reducing the peak in turbulence intensity because wakes generated by different sized elements interact at different distances' downstream. Diffusivity increases as a consequence of this mechanism 14 because, from a Lagrangian perspective, a fluid element may potentially move from one wake to a larger one as it progresses downstream, with each larger wake having a larger eddy turnover time. In the theory of decaying homogeneous turbulence, it is usually considered that 61…”

Section: Discussionmentioning

confidence: 99%

“…9 In the last decade, there has been a concerted effort to understand the implications of forcing the flow at multiple scales. [10][11][12][13][14] This work has focused primarily on characterizing the dissipation properties of freely decaying, multiscale-forced turbulence, with connections noted to notions of exponential decay. 15,16 In addition, numerical simulation has elucidated the mechanisms by which multiscale forcing operates 17,18 and recent work has also begun to explore the implications of multiscale forcing for pipe and boundary-layer flows.…”

Section: Introductionmentioning

confidence: 99%

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Gradual wavelet reconstruction of the velocity increments for turbulent wakes

2015

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This work explores the properties of the velocity increment distributions for wakes of contrasting local Reynolds number and nature of generation (a cylinder wake and a multiscale-forced case, respectively). It makes use of a technique called gradual wavelet reconstruction (GWR) to generate constrained randomizations of the original data, the nature of which is a function of a parameter, ϑ. This controls the proportion of the energy between the Markov-Einstein length (∼ 0.8 Taylor scales) and integral scale that is fixed in place in the synthetic data. The properties of the increments for these synthetic data are then compared to the original data as a function of ϑ. We write a Fokker-Planck equation for the evolution of the velocity increments as a function of spatial scale, r, and, in line with previous work, expand the drift and diffusion terms in terms up to fourth order in the increments and find no terms are relevant beyond the quadratic terms. Only the linear contribution to the expansion of the drift coefficient is non-zero and it exhibits a consistent scaling with ϑ for different flows above a low threshold. For the diffusion coefficient, we find a local Reynolds number independence in the relation between the constant term and ϑ for the multiscale-forced wakes. This term characterizes small scale structure and can be contrasted with the results for the Kolmogorov capacity of the zero-crossings of the velocity signals, which measures structure over all scales and clearly distinguishes between the types of forcing. Using GWR shows that results for the linear and quadratic terms in the expansion of the diffusion coefficient are significant, providing a new means for identifying intermittency and anomalous scaling in turbulence datasets. All our data showed a similar scaling behavior for these parameters irrespective of forcing type or Reynolds number, indicating a degree of universality to the anomalous scaling of turbulence. Hence, these terms are a useful metric for testing the efficacy of synthetic turbulence generation schemes used in large eddy simulation, and we also discuss the implications of our approach for reduced order modeling of the Navier-Stokes equations.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Gradual wavelet reconstruction of the velocity increments for turbulent wakes

2015

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“…Hence, there needs to be an engagement with new work on turbulent dissipation [Vassilicos, 2015], the role of complex forcings [Hurst and Vassilicos, 2007;Nagata et al, 2013;Keylock et al, 2012c] and the modulation of small scales by the large [Ganapathisubramani et al, 2003;Hutchins et al, 2011]. These phenomena exhibit connections to older work on interscale coupling [Ohkitani and Kida, 1992] and intermittency [Kolmogorov, 1962], as well as more recent studies of velocity-intermittency coupling Keylock et al, 2012b].…”

Section: Resultsmentioning

confidence: 99%

“…However, to understand dissipation a more careful consideration of the organization of the various elements is needed that goes beyond porosity. These need to be parameterized in some way, and it is suggested here that, based on recent work in the literature [Hurst and Vassilicos, 2007;Seoud and Vassilicos, 2007;Nagata et al, 2013;Keylock et al, 2012c] the fractal dimension of the forcing object provides a starting point. This then needs to be complemented by lacunarity and succolarity of the forcing [de Melo and Conci, 2013].…”

Section: Supplementing Formulations Of Length Scales For Complex Turbmentioning

confidence: 99%

Flow resistance in natural, turbulent channel flows: The need for a fluvial fluid mechanics

Keylock

2015

Water Resources Research

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In fluvial environments, feedbacks among flow, bed forms, sediment, and macrophytes result in a complex fluid dynamics. The assumptions underpinning standard tools in hydraulics are commonly violated and alternative approaches must be formulated. I argue that we should question the assumption that classical notions in fluid mechanics provide the foundations for the techniques of the future. Recent work on turbulent dissipation, interscale modulation of the dynamics, intermittency, and the role of complex forcings is discussed. An agenda for future work is proposed that involves improving our characterization of complex forcings and developing better understanding of the behavior of the velocity gradient tensor in complex, fluvial environments. This leads to the formulation of modeling tools relevant to fluvial fluid mechanics, rather than a reliance on methods developed elsewhere. One avenue by which such methods might be developed is suggested based on the stretched spiral vortex as a baseline topology. This would result in a nonequilibrium model for turbulence that has greater potential to capture the dynamics in which we are interested. Although these ideas are raised in the context of a future fluvial fluid mechanics, they are applicable to any situation where turbulent flows are forced in complicated ways.

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“…This is argued to be the case because even though the fraction of the total energy contained in the smallscales K η decreases with the Reynolds numbers, the associated time-scale τ η also becomes vanishingly small and it can be shown that K η /τ η ∝ ε and thus finite. This can be argued to be the root cause for the significant imbalance between Π(k) and ε reported for non-stationary homogeneous turbulence and the manifestations of nonequilibrium dissipation behaviour observed in recent experiments and simulations [8,[19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Spectral imbalance in the inertial range dynamics of decaying rotating turbulence

Valente

Dallas

2017

Phys. Rev. E

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Direct numerical simulations of homogeneous decaying turbulence with mild background rotation show the existence of a systematic and significant imbalance between the non-linear energy cascade to small scales and its dissipation. By starting the decay from a statistically stationary and fully developed rotating turbulence state, where the dissipation and the energy flux are approximately equal, the data shows a growing imbalance between the two until a maximum is reached when the dissipation is about twice the energy flux. This dichotomy of behaviours during decay is reminiscent of the non-equilibrium and the equilibrium regions previously reported for non-rotating turbulence [P.C. Valente, J.C. Vassilicos, Phys. Rev. Lett. 108 214503 (2012)]. Note, however, that for decaying rotating turbulence the classical scaling of the dissipation rate ǫ ∝ u ′3 /L (where u ′ and L are the root mean square fluctuating velocity and the integral length scale, respectively) does not appear to hold during decay, which may be attributed to the effect of the background rotation on the energy cascade. On the other hand, the maximum energy flux holds the scaling Πmax ∝ u ′3 /L in the initial stage of the decay until the maximum imbalance is reached.

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Turbulence structure and turbulence kinetic energy transport in multiscale/fractal-generated turbulence

Cited by 95 publications

References 16 publications

Gradual wavelet reconstruction of the velocity increments for turbulent wakes

Gradual wavelet reconstruction of the velocity increments for turbulent wakes

Flow resistance in natural, turbulent channel flows: The need for a fluvial fluid mechanics

Spectral imbalance in the inertial range dynamics of decaying rotating turbulence

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