Structure and Dynamics of Vorticity in Turbulence

Schumacher, Jörg; Kerr, Robert M.; Horiuti, Kiyosi

doi:10.1017/cbo9781139032810.003

Cited by 3 publications

(5 citation statements)

References 108 publications

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“…A three-dimensional (3D) incompressible turbulent flow has a peculiar geometrical structure which distinguishes it from a purely random field. The visualization of the isosurfaces of enstrophy and energy dissipation indeed indicates that vorticity concentrates into tubular structures, while regions of intense strain are sheet-like [1] (see figure 1 for a visualization based on the Q-criterion [2,3]). Several Lagrangian studies have shown that the dynamics of objects smaller than the viscous-dissipation scale can depend sensitively on the nature of the local velocity gradient.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of a long chain in turbulent flows: impact of vortices

Picardo

Singh

Ray

et al. 2020

Phil. Trans. R. Soc. A.

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We show and explain how a long bead–spring chain, immersed in a homogeneous isotropic turbulent flow, preferentially samples vortical flow structures. We begin with an elastic, extensible chain which is stretched out by the flow, up to inertial-range scales. This filamentary object, which is known to preferentially sample the circular coherent vortices of two-dimensional (2D) turbulence, is shown here to also preferentially sample the intense, tubular, vortex filaments of three-dimensional (3D) turbulence. In the 2D case, the chain collapses into a tracer inside vortices. In the 3D case on the contrary, the chain is extended even in vortical regions, which suggests that the chain follows axially stretched tubular vortices by aligning with their axes. This physical picture is confirmed by examining the relative sampling behaviour of the individual beads, and by additional studies on an inextensible chain with adjustable bending-stiffness. A highly flexible, inextensible chain also shows preferential sampling in three dimensions, provided it is longer than the dissipation scale, but not much longer than the vortex tubes. This is true also for 2D turbulence, where a long inextensible chain can occupy vortices by coiling into them. When the chain is made inflexible, however, coiling is prevented and the extent of preferential sampling in two dimensions is considerably reduced. In three dimensions, on the contrary, bending stiffness has no effect, because the chain does not need to coil in order to thread a vortex tube and align with its axis. This article is part of the theme issue ‘Fluid dynamics, soft matter and complex systems: recent results and new methods’.

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Section: Introductionmentioning

confidence: 99%

Dynamics of a long chain in turbulent flows: impact of vortices

Picardo

Singh

Ray

et al. 2020

Phil. Trans. R. Soc. A.

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show abstract

“…A three-dimensional (3D) incompressible turbulent flow has a peculiar geometrical structure which distinguishes it from a purely random field. The visualisation of the isosurfaces of enstrophy and energy dissipation indeed indicates that vorticity concentrates into tubular structures, while regions of intense strain are sheet-like [1] (see Fig. 1 for a visualization based on the Q-criterion [2]).…”

Section: Introductionmentioning

confidence: 89%

Dynamics of a long chain in turbulent flows: Impact of vortices

Picardo,

Singh,

Ray

et al. 2019

Preprint

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We show and explain how a long bead-spring chain, immersed in a homogeneous, isotropic turbulent flow, preferentially samples vortical flow structures. We begin with an elastic, extensible chain which is stretched out by the flow, up to inertial-range scales. This filamentary object, which is known to preferentially sample the circular coherent vortices of two-dimensional (2D) turbulence, is shown here to also preferentially sample the intense, tubular, vortex filaments of 3D turbulence. In the 2D case, the chain collapses into a tracer inside vortices. In 3D, on the contrary, the chain is extended even in vortical regions, which suggests that it follows axially-stretched tubular vortices by aligning with their axes. This physical picture is confirmed by examining the relative sampling behaviour of the individual beads, and by additional studies on an inextensible chain with adjustable bending-stiffness. A highly-flexible, inextensible chain also shows preferential sampling in 3D, provided it is longer than the dissipation scale, but not much longer than the vortex tubes. This is true also for 2D turbulence, where a long inextensible chain can occupy vortices by coiling into them. When the chain is made inflexible, however, coiling is prevented and the extent of preferential sampling in 2D is considerably reduced. In 3D, on the contrary, bending stiffness has no effect, because the chain does not need to coil in order to thread a vortex tube and align with its axis.

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“…Turbulence is riddled with a hierarchy of interacting vortical and straining structures ( Fig. 1), which are closely related to its characteristic intermittent and non-Gaussian statistics [1][2][3][4][5][6]. The most intense structures typically occur near each other, in the form of vortex tubes surrounded by straining sheets, as shown in Fig.…”

mentioning

confidence: 99%

“…The strain (vorticity) dominated portion of this plot is shaded in blue (red), and corresponds to Q < −0.3 (Q > +0. 3).…”

mentioning

confidence: 99%

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Flow structures govern particle collisions in turbulence

et al. 2019

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The role of the spatial structure of a turbulent flow in enhancing particle collision rates in suspensions is an open question. We show and quantify, as a function of particle inertia, the correlation between the multiscale structures of turbulence and particle collisions: Straining zones contribute predominantly to rapid head-on collisions compared to vortical regions. We also discover the importance of vortex-strain worm-rolls, which goes beyond ideas of preferential concentration and may explain the rapid growth of aggregates in natural processes, such as the initiation of rain in warm clouds. * jrpicardo@icts.res.in;

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Structure and Dynamics of Vorticity in Turbulence

Cited by 3 publications

References 108 publications

Dynamics of a long chain in turbulent flows: impact of vortices

Dynamics of a long chain in turbulent flows: impact of vortices

Dynamics of a long chain in turbulent flows: Impact of vortices

Flow structures govern particle collisions in turbulence

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