New Insights into Turbulent Spots

Wu, Xiaohua

doi:10.1146/annurev-fluid-120720-021813

Cited by 10 publications

(7 citation statements)

References 173 publications

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“…As the Yukawa potential is an explicit function of distance, r; therefore, the force on each grain is obtained by taking the negative gradient of the Yukawa potential. The force on i th grain, obtained from the negative gradient of Yukawa potential, is given in equation (1).…”

Section: Simulation Detailsmentioning

confidence: 99%

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Turbulent spot formation in three-dimensional yukawa liquids using large-scale molecular dynamics simulation—effect of system size

Kalita,

Ganesh

2024

Phys. Scr.

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We have performed classical ``first principles'' 3D Molecular Dynamics (MD) simulation of plane-Couette flow (PCF) in a 3D Yukawa liquid. The main aim of the present investigation is to study the effect of stream-wise (flow-direction) and span-wise (transverse direction to the flow) width on the subcritical transition to turbulence in plane Couette flow (PCF), separately. In the past, taking very large-aspect ratio systems, subcritical transition to turbulence in PCF has been studied in great detail. However, the effect of stream-wise and span-wise width on the turbulent dynamics separately, have not been studied in detail. In the present work, we have investigated the effect of stream-wise and span-wise width or length and found that the stream-wise length enhances the large-scale energy, which gives rise to strong large-scale flow, and span-wise width enhances the small-scale energy, which gives rise to strong small-scale structures. In other words, topology of the turbulent spot is observed to change with the change in system size. The spectral separation between the modes governing the large and small-scale dynamics improves with the increase in system sizes. The connection between the stream-wise vortices and the stream-wise velocity streaks is investigated in details. We have found that the number stream-wise velocity streaks is one unit larger than the number of stream-wise vortices. A qualitative comparison between the results obtained from the MD simulation and the hydrodynamics experiment is presented in this article. The behavior of the system was observed to vary with the range of interactions among the dust grains.

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Section: Simulation Detailsmentioning

confidence: 99%

“…When a Plane Couette flow (PCF) is turbulent, localized patterns or turbulent spots are observed to form in the flow [1,2]. The transition to turbulence in PCF is known to be subcritical [3,4], as the base velocity profile is linearly stable for infinitesimal perturbation for all the values of Reynolds number (Re) [5].…”

Section: Introductionmentioning

confidence: 99%

Turbulent spot formation in three-dimensional yukawa liquids using large-scale molecular dynamics simulation—effect of system size

Kalita,

Ganesh

2024

Phys. Scr.

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“…A hairpin vortex (Zhou et al 1999) emerges from the streaks in figure 7(c), and then it evolves into a hairpin packet by the auto-generation mechanism (Adrian et al 2000;Adrian 2007;Kim et al 2008). The vortices break down and form a turbulent spot in figure 7(d), which eventually leads to a fully developed turbulent state (Wu 2023).…”

Section: Transition Induced By Vortex Burstingmentioning

confidence: 99%

“…Subsequently, the instability of streaks (Ricco, Luo & Wu 2011;Wu 2019;Xu et al 2023), Tollmien-Schlichting (TS) waves (Sandham & Kleiser 1992;Schlatter, Stolz & Kleiser 2004) and Λand hairpin-like vortices (Sandham & Kleiser 1992;Zhao et al 2016) promote the transition process. Finally, the emergence of turbulent spots (Wu 2023) signals the onset of turbulence.…”

Section: Introductionmentioning

confidence: 99%

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Transition induced by a bursting vortex ring in channel flow

Wang,

Yang

2024

J. Fluid Mech.

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We investigate the influence of vortices remote from the boundary on the near-wall flow dynamics in wall-bounded flows. A vortex ring with precisely controlled local twist is introduced into the outer layer of a channel flow at a moderate Reynolds number. We find that the minimum vorticity flux for triggering the transition to turbulence is significantly reduced from the initial disturbance of an untwisted vortex ring to that of a twisted ring. In particular, the latter disturbance can cause vortex bursting in the early transitional stage. The impact of vortex bursting on the transition process is characterised by the near-wall, wall-normal velocity with the rapid distortion theory. The wall-normal velocity grows during vortex bursting, and leads to streak formation and then the transition to turbulence. The notable wall-normal velocity is induced by the large di-vorticity generated in vortex bursting. We model the growing radial component of the di-vorticity in terms of the local twist, and demonstrate that its surge is due to the generation of highly twisted vortex lines in vortex bursting. Then, we derive that the generation of the di-vorticity in the outer layer enhances the wall-normal velocity in the inner layer via the Poisson equation with the image method and the multipole expansion. Thus, we elucidate that the vortex bursting can have an effect on the transition process.

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