Metamorphosis of a hairpin vortex into a young turbulent spot

Bart, A.; Ronald, D Joslin

doi:10.1063/1.868363

Cited by 113 publications

(78 citation statements)

References 25 publications

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“…"Vortex Breakdown" has been widely spread in many research papers and textbooks [5,[9][10][11]. However, our analysis found that "Vortex Breakdown" is theoretically impossible.…”

Section: Vortexmentioning

confidence: 44%

“…In practice, "Vortex Breakdown" can never happen. It is found that "Vortex Breakdown" described by exiting publications [5,9,10] is either misinterpreted by 2D visualization or by using the pressure center as the vortex center.…”

Section: Vortexmentioning

confidence: 99%

“…U-shaped vortex [9] or barrel-shaped wave [5] is still a mystery and thought as a newly formed secondary vortex or waves. However, it is found by our new DNS that the U-shaped vortex was an original coherent structure and it is a tertiary (not secondary) vortex with same vorticity sign as the ring legs.…”

Section: U-shapedmentioning

confidence: 99%

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New Findings by High‐Order DNS for Late Flow Transition in a Boundary Layer

Liu

Lin

Lü

2011

Modelling and Simulation in Engineering

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This paper serves as a summary of new discoveries by DNS for late stages of flow transition in a boundary layer. The widely spread concept "vortex breakdown" is found theoretically impossible and never happened in practice. The ring-like vortex is found the only form existing inside the flow field. The ring-like vortex formation is the result of the interaction between two pairs of counterrotating primary and secondary streamwise vortices. Following the first Helmholtz vortex conservation law, the primary vortex tube rolls up and is stretched due to the velocity gradient. In order to maintain vorticity conservation, a bridge must be formed to link two Λ-vortex legs. The bridge finally develops as a new ring. This process keeps going on to form a multiple ring structure. The U-shaped vortices are not new but existing coherent vortex structure. Actually, the U-shaped vortex, which is a third level vortex, serves as a second neck to supply vorticity to the multiple rings. The small vortices can be found on the bottom of the boundary layer near the wall surface. It is believed that the small vortices, and thus turbulence, are generated by the interaction of positive spikes and other higher level vortices with the solid wall. The mechanism of formation of secondary vortex, second sweep, positive spike, high shear distribution, downdraft and updraft motion, and multiple ring-circle overlapping is also investigated.

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“…"Vortex Breakdown" has been widely spread in many research papers and textbooks [5,[9][10][11]. However, our analysis found that "Vortex Breakdown" is theoretically impossible.…”

Section: Vortexmentioning

confidence: 44%

Section: Vortexmentioning

confidence: 99%

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New Findings by High‐Order DNS for Late Flow Transition in a Boundary Layer

Liu

Lin

Lü

2011

Modelling and Simulation in Engineering

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“…Sustained efforts have been devoted to study properties and dynamics of transitional-turbulent spots (TRTSs) in the natural or bypass transitions of the ZPGSFPBL (18)(19)(20)(21)(22). It was long hoped that information extracted from TRTS during the inception of boundary-layer turbulence might shed light on the inner-layer dynamics, transport processes, and turbulence regeneration of the fully turbulent ZPGSFPBL.…”

mentioning

confidence: 99%

Transitional–turbulent spots and turbulent–turbulent spots in boundary layers

Moin

Wallace

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

102

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Two observations drawn from a thoroughly validated direct numerical simulation of the canonical spatially developing, zero-pressure gradient, smooth, flat-plate boundary layer are presented here. The first is that, for bypass transition in the narrow sense defined herein, we found that the transitional-turbulent spot inception mechanism is analogous to the secondary instability of boundary-layer natural transition, namely a spanwise vortex filament becomes a Λ vortex and then, a hairpin packet. Long streak meandering does occur but usually when a streak is infected by a nearby existing transitionalturbulent spot. Streak waviness and breakdown are, therefore, not the mechanisms for the inception of transitional-turbulent spots found here. Rather, they only facilitate the growth and spreading of existing transitional-turbulent spots. The second observation is the discovery, in the inner layer of the developed turbulent boundary layer, of what we call turbulent-turbulent spots. These turbulent-turbulent spots are dense concentrations of small-scale vortices with high swirling strength originating from hairpin packets. Although structurally quite similar to the transitional-turbulent spots, these turbulent-turbulent spots are generated locally in the fully turbulent environment, and they are persistent with a systematic variation of detection threshold level. They exert indentation, segmentation, and termination on the viscous sublayer streaks, and they coincide with local concentrations of high levels of Reynolds shear stress, enstrophy, and temperature fluctuations. The sublayer streaks seem to be passive and are often simply the rims of the indentation pockets arising from the turbulent-turbulent spots.boundary layer | transition | turbulence | direct numerical simulation T he zero-pressure gradient, smooth, flat-plate boundary layer (ZPGSFPBL) is the simplest viscous external flow. It serves as the idealized limiting case and calibration benchmark of atmospheric and oceanic planetary boundary layers as well as aeronautical, maritime, and automotive boundary-layer flows. For over 60 y since the work by Theodorsen (1), a central theme in fundamental fluid mechanics research has been the search for the constitutive coherent structure in the turbulent ZPGSFPBL, particularly inside the near-wall/inner layer less than ∼100 viscous units away from the plate where the production and dissipation of turbulence kinetic energy reach their peaks (2-6). When the nature of the inner-layer structure and dynamics is thoroughly understood, this understanding can be incorporated in turbulence theory and predictive modeling.Decades of research have produced an apparent consensus view (7-9) that the inner layer, which consists of the buffer layer and the viscous sublayer, of a turbulent ZPGSFPBL is populated by randomly distributed quasistreamwise vortices as well as elongated high-and low-momentum streaks. Streaks are thought to actively participate in a self-sustaining bursting cycle that includes streak generation, lift up, oscil...

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“…Robinson [2] confirmed the existence of non-symmetric archand quasi-streamwise vortices on the basis of the evaluation of DNS results. Studies involving the dynamics of hairpin vortices in the boundary layer have been performed by Perry & Chong [3], Acarlar & Smith [4,5], Smith et al [6], Haidari & Smith [7] and Singer & Joslin [8]. On these bases, a picture of vortex generation and reciprocal interaction in the boundary layer emerges in which processes of interaction of existing vortices with wall-layer fluid involve viscous-inviscid interaction, generation of new vorticity, redistribution of existing vorticity, vortex stretching near the wall and vortex relaxation in the outer region.…”

Section: Introductionmentioning

confidence: 99%

Vortex Identification in the Wall Region of Turbulent Channel Flow

Alfonsi

Primavera

2007

Computational Science – ICCS 2007

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Abstract. Four widely-used techniques for vortex detection in turbulent flows are investigated and compared. The flow of a viscous incompressible fluid in a plane channel is simulated numerically by means of a parallel computational code based on a mixed spectral-finite difference algorithm for the numerical integration of the Navier-Stokes equations. The DNS approach (Direct Numerical Simulation) is followed in the calculations, performed at friction Reynolds number 180 = τ Re. A database representing the turbulent statistically steady state of the velocity field through 10 viscous time units is assembled and the different vortex-identification techniques are applied to the database. It is shown that the method of the "imaginary part of the complex eigenvalue pair of the velocity-gradient tensor" gives the best results in identifying hairpin-like vortical structures in the wall region of turbulent channel flow.

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Metamorphosis of a hairpin vortex into a young turbulent spot

Cited by 113 publications

References 25 publications

New Findings by High‐Order DNS for Late Flow Transition in a Boundary Layer

New Findings by High‐Order DNS for Late Flow Transition in a Boundary Layer

Transitional–turbulent spots and turbulent–turbulent spots in boundary layers

Vortex Identification in the Wall Region of Turbulent Channel Flow

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