Coherent near-wall structures and drag reduction by spanwise forcing

Gallorini, Emanuele; Quadrio, Maurizio; Gatti, Davide

doi:10.1103/physrevfluids.7.114602

Cited by 9 publications

(15 citation statements)

References 32 publications

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“…The quasi-streamwise vortices react differently from control: δv δv m moves from Y + = 53 in the reference case to Y + = 55 for T + = 75 and to Y + = 43 for T + = 250. These contrasting trends are consistent with the wall-normal displacement found by Gallorini et al (2022) for conditionally averaged quasi-streamwise vortices, but are extracted from the present analysis without the need for an (inevitably subjective) procedure for conditional structure extraction.…”

Section: Description At a Fixed Phasesupporting

confidence: 87%

“…Similarly, the evolution of the wall-normal position Y m of δw δw m (or, equivalently, of δu δu m ) quantifies the vertical displacement of the streaks during the cycle. that is conventionally used to describe the tilting angle of the near-wall structures (Yakeno et al 2014;Gallorini et al 2022). The two quantities θ and θ s are quantitatively similar and present the same phase dependence, with a nearly constant difference of approximately 8 • .…”

Section: Evolution During the Cyclementioning

confidence: 99%

“…In this appendix, the interpretations of the local maxima of δw δw in the r x = r y = 0 and r z = r y = 0 planes provided in § 4.1.2 are supported by inspecting the velocity field induced by the conditionally averaged quasi-streamwise vortex at different phases of the control cycle. The procedure to extract the conditional average from the direct numerical simulation database closely resembles that presented by Jeong et al (1997); it is described in detail by Gallorini et al (2022) and is not repeated here.…”

Section: Structure Functions With Triple Decompositionmentioning

confidence: 99%

“…The AGKE terms are computed from two datasets obtained by direct numerical simulations. They are described by Gallorini, Quadrio & Gatti (2022), where the interested reader can find full details.…”

Section: Turbulent Drag Reduction By a Spanwise-oscillating Wallmentioning

confidence: 99%

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Structure function tensor equations with triple decomposition

et al. 2023

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Exact budget equations are derived for the coherent and stochastic contributions to the second-order structure function tensor. They extend the anisotropic generalised Kolmogorov equations (AGKE) by considering the coherent and stochastic parts of the Reynolds stress tensor, and are useful for the statistical description of turbulent flows with periodic or quasi-periodic features, like, for example, the alternate shedding after a bluff body. While the original AGKE describe production, transport, inter-component redistribution and dissipation of the Reynolds stresses in the combined space of scales and positions, the new equations, called $\varphi$ AGKE, contain the phase $\varphi$ as an additional independent variable, and describe the interplay among the mean, coherent and stochastic fields at the various phases. The newly derived $\varphi$ AGKE are then applied to a case where an exactly periodic external forcing drives the flow: a turbulent plane channel flow modified by harmonic spanwise oscillations of the wall to reduce drag. The phase-by-phase action of the oscillating transversal Stokes layer generated by the forcing on the near-wall turbulent structures is observed, and a detailed description of the scale-space interaction among mean, coherent and stochastic fields is provided thanks to the $\varphi$ AGKE.

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Section: Description At a Fixed Phasesupporting

confidence: 87%

Section: Evolution During the Cyclementioning

confidence: 99%

Section: Structure Functions With Triple Decompositionmentioning

confidence: 99%

Section: Turbulent Drag Reduction By a Spanwise-oscillating Wallmentioning

confidence: 99%

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Structure function tensor equations with triple decomposition

et al. 2023

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“…We conclude by noting that the findings here presented are likely to add relevant phenomenological information to the discussion of fundamentally important issues in pipe flow turbulence, as drag control and particle-laden dynamics, once they are closely connected to the statistical features of near-wall coherent structures [18][19][20][21][22][23].…”

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confidence: 64%