# gst: apropos of 1or2achoos (e.g. from Wuhan), the dynamics of turbulence in a fluid puff

<< Turbulence is everywhere -- in the movement of the wind, the ocean waves and even magnetic fields in space. It can also be seen in more transient phenomena, like smoke billowing from a chimney, or a cough. (..) Understanding this latter type of turbulence -- called puff turbulence -- is important not only for the advancement of fundamental science, but also for practical health and environmental measures, >>️

<< The very nature of turbulence is chaotic, so it's hard to predict, (..) Puff turbulence, which occurs when the ejection of a gas or liquid into the environment is disrupted, rather than continuous, has more complicated characteristics, so it's even more challenging to study. But it's of vital importance -- especially right now for understanding airborne transmission of viruses like SARS-CoV-2. >>️ Marco Edoardo Rosti. 

<< The new model, (..) includes how minute fluctuations within the puff behave, and how both large-scale and small-scale dynamics are impacted by changes in temperature and humidity. (..) at cooler temperatures (15°C or lower), (AA) model deviated from the classical model for turbulence. >>️

<< In the classical model, turbulence reigns supreme -- determining how all the little swirls and eddies within the flow behave. But once temperatures dipped, buoyancy started to have a greater impact. >>

<< The effect of buoyancy was initially very unexpected. It's a completely new addition to the theory of turbulent puffs,>> Marco Edoardo Rosti. ️

Secrets of COVID-19 transmission revealed in turbulent puffs. Okinawa Institute of Science and Technology (OIST). Aug 26, 2021. 

https://www.sciencedaily.com/releases/2021/08/210826111729.htm

Andrea Mazzino, Marco Edoardo Rosti. Unraveling the Secrets of Turbulence in a Fluid Puff. Phys. Rev. Lett. 127, 094501. Aug 25, 2021. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.094501

Also

keyword 'drop' | 'droplet' in FonT:

https://flashontrack.blogspot.com/search?q=drop

https://flashontrack.blogspot.com/search?q=droplet

keyword 'turbulence' in FonT:

https://flashontrack.blogspot.com/search?q=turbulence

keyword 'turbolento' | 'turbolenza' in Notes (quasi-stochastic poetry): 

https://inkpi.blogspot.com/search?q=turbolento

https://inkpi.blogspot.com/search?q=turbolenza

keyword 'virus' | 'sars-cov-2' | 'sars' in FonT: 

https://flashontrack.blogspot.com/search?q=virus

https://flashontrack.blogspot.com/search?q=sars-cov-2

https://flashontrack.blogspot.com/search?q=sars

keyword 'virus' in Notes (quasi-stochastic poetry):

https://inkpi.blogspot.com/search?q=virus

# gst: when a turbulence can be confined

<< Turbulence is hard to control. Its ephemeral nature prevents us from treating it as an ordinary state of matter. Here (AA) create a stationary and isolated blob of turbulence using only elemental building blocks: vortex rings.  The turbulence is confined in a spherical region, surrounded by a quiescent environment, initiated and sustained by vortex rings. Crucially, vortex rings can be endowed with conserved quantities such as energy and helicity, which can be transferred to the turbulent state. Using 2D particle image velocimetry and 3D particle tracking velocimetry, (AA) demonstrate how confinement of turbulence occurs when vortex rings repeatedly collide, in contrast to coherent vortex reconnections. The pathlines depict the difference between these states of flow. >>️

Takumi Matsuzawa, Noah P. Mitchell, Stéphane Perrard, William T. M. Irvine. Turbulence through sustained vortex ring collisions. Phys. Rev. Fluids 8, 110507. Nov 16, 2023.

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.8.110507

75TH ANNUAL MEETING OF THE APS DIVISION OF FLUID DYNAMICS (NOVEMBER 20, 2022 — NOV 22, 2022). V0008: Turbulence through sustained vortex ring collisions. 

https://doi.org/10.1103/APS.DFD.2022.GFM.V0008

Also: turbulence, vortex, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, turbulence, vortex, vortex ring collisions

# gst: random walk model for dual cascades in wave turbulence.

<< Dual cascades in turbulent systems with two conserved quadratic quantities famously arise in both two-dimensional hydrodynamic turbulence and also in wave turbulence based on four-wave interactions. >>

<< in wave turbulence the systematic spectral fluxes observed in a dual cascade do not require an irreversible dynamical mechanism, rather, they arise as the inevitable outcome of blind chance. >>️️

Oliver Bühler. Random walk model for dual cascades in wave turbulence. Phys. Rev. E 109, 055102. May 1, 2024. 

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.109.055102

Also: waves, turbulence, random, weak, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, waves, turbulence, weak turbulence, random, random walks

# gst: when turbulence is driven by a strongly compressive guide

<< it is not fully understood how shocks drive turbulence, in particular whether shock driving is a more solenoidal (rotational, divergence-free) or a more compressive (potential, curl-free) mode of driving turbulence. >>️

<< Here, (AA) use hydrodynamical simulations of a shock inducing turbulent motions in a structured, multi-phase medium. >>️

<< Using simulations in which a shock is driven into a multi-phase medium with structures of different sizes and Γ<1, (AA) find b∼1 for all cases, showing that shock-driven turbulence is consistent with strongly compressive driving. >>️

Saee Dhawalikar, Christoph Federrath,  et al. The driving mode of shock-driven turbulence. arXiv:2205.14417v1 [astro-ph.GA]. May 28, 2022. 

https://arxiv.org/abs/2205.14417

Also

keywords 'turbulence' in FonT

https://flashontrack.blogspot.com/search?q=turbulence

keywords 'turbolento' in Notes 

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=turbolento

keyword 'waves' in FonT

https://flashontrack.blogspot.com/search?q=waves

keyword 'onda' in Notes 

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=onda

keyword 'instability' | 'instabilities' in FonT

https://flashontrack.blogspot.com/search?q=instability

https://flashontrack.blogspot.com/search?q=instabilities

keyword 'instabile' in Notes 

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=instabile

Keywords: gst, turbulence, instability, waves, shock waves

# jazz: when turbulence underneath it and on top of it.

<< The album title comes from poet and scholar Fred Moten, who described Gamedze's drumming in the internet forum Poesis as an "amazing interplay between turbulence and pulse. Pulse is supposed to regulate and also be regular, but the turbulence underneath it and on top of it, it's just extraordinary." >>️

Thom Jurek. Turbulence and Pulse. allmusic.com. May 5, 2023. 

https://www.allmusic.com/album/turbulence-and-pulse-mw0003947563?1684082977357 

Also: jazz, turbulence, in  https://www.inkgmr.net/kwrds.html

Keywords: jazz, turbulence

# gst: apropos of waves perturbed by weak turbulences

<< Wave phenomena are ubiquitous at all scales throughout the Universe, and where there are waves, there’s the potential for wave turbulence. Wave turbulence is the physical state that arises in a continuous medium when a large number of wave modes interact with each other randomly. >>

<< A specific case of wave turbulence in which weakly nonlinear waves propagate in an unbounded space is described by weak turbulence theory. Capturing the dynamics of this regime will be helpful to accurately model large fluid systems. >>

<< In a rotating fluid, the predicted wave spectrum for interacting weakly nonlinear inertial waves is perturbed by the formation of geostrophic modes—columnar vortices aligned with the rotation axis (..) (AA) successfully suppress geostrophic modes with the addition of two honeycomb-patterned plates, allowing them to confirm the predictions of weak turbulence theory. >>

Sergey Nazarenko. Verifying Weak Turbulence Theory.  Physics 13, 194. Dec 14, 2020. 

https://physics.aps.org/articles/v13/194

Eduardo Monsalve, Maxime Brunet, et al. Quantitative Experimental Observation of Weak Inertial-Wave Turbulence. Phys. Rev. Lett. 125, 254502. Dec 14, 2020.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.254502

# gst: transitional dynamics among gyrotactic (prolate spheroid) swimmers in turbulence

<< In this study, (AA) consider small, elongated, gyrotactic, swimming particles in homogenous isotropic turbulence (..). Many motile phytoplankton species are gyrotactic, i.e., their swimming direction results from the competition between shear-induced viscous torque and the stabilizing torque due to bottom-heaviness. (..)  Moreover, both single phytoplankton cells and multicellular phytoplankton chains can have elongated shapes, which makes the study of gyrotactic active particles with prolate shapes necessary. >>

AA addressed the following problems:

<< (i) How the clustering is affected by the swimming number Φ and the stability number Ψ? In particular, how to characterize the extent of clustering based on the three-dimensional Voronoi analysis?

(ii) How the clustering is related to the flow structures? This question has two perspectives.  From the space perspective, what are the regions that particles accumulate in? From the time perspective, how long do particles exist in an aggregated state? >>

Zehua Liu, Linfeng Jiang, Chao Sun. Accumulation and alignment of elongated gyrotactic swimmers in turbulence. arXiv:2202.04351v1 [physics.flu-dyn]. Feb 9, 2022.

https://arxiv.org/abs/2202.04351

Also

The effect of noise on the dynamics of microswimmers in externally-driven fluid flows.  

https://flashontrack.blogspot.com/2021/10/gst-effect-of-noise-on-dynamics-of.html

keywords 'turbulence' in FonT   

https://flashontrack.blogspot.com/search?q=turbulence

keywords 'turbolento' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=turbolento

keywords: transition, swimmers,  gyrotactic swimmers, spheroids,  prolate spheroids, stability, turbulence

# gst: towards (insights into) intermittency and inhomogeneity of turbulent mixing

<< Fluid elements deform in turbulence by stretching and folding. In this work, by projecting the material deformation tensor onto the largest stretching direction, the dynamics of folding is depicted through the evolution of the material curvature. Results from direct numerical simulation (DNS) show that the curvature growth exhibits two regimes, first a linear stage dominated by folding fluid elements through a persistent velocity Hessian which then transitions to an exponential growth driven by the stretching of already strongly bent fluid elements. This transition leads to strong curvature intermittency at later stages, which can be explained by a proposed curvature-evolution model. The link between velocity Hessian to folding provides a new way to understand the crucial steps in energy cascade and mixing in turbulence beyond the classical linear description. >>

Yinghe Qi, Charles Meneveau, Greg Voth, Rui Ni. Folding dynamics and its intermittency in turbulence. arXiv: 2301.10341v1 [physics.flu-dyn]. Jan 24, 2023. 

https://arxiv.org/abs/2301.10341

Also

keyword 'intermittency' in FonT

https://flashontrack.blogspot.com/search?q=intermittency

keyword 'turbulence' in FonT

https://flashontrack.blogspot.com/search?q=turbulence

keyword 'turbolento' | 'turbolenza' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=turbolento

https://inkpi.blogspot.com/search?q=turbolenza

keyword 'transition' | 'transitional' in FonT

https://flashontrack.blogspot.com/search?q=transition

https://flashontrack.blogspot.com/search?q=transitional

keyword 'transition' | 'transizion*' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=transition

https://inkpi.blogspot.com/search?q=transizione

https://inkpi.blogspot.com/search?q=transizioni

Keywords: gst, intermittency, turbulence, transition

# gst: apropos of transitions, perspectives on viscoelastic flow instabilities; the 'porous individualism'

<< given the observation that disorder can suppress the transition to elastic turbulence in 2D porous media (..), it has been unclear whether and how this transition manifests in disordered 3D media — though elastic turbulence has been speculated to underlie the long-standing observation that the macroscopic flow resistance of an injected polymer solution can abruptly increase above a threshold flow rate in a porous medium, but not in bulk solution >>️

AA << found that the transition to unstable flow in each pore is continuous, arising due to the increased persistence of discrete bursts of instability above a critical value of the characteristic (Weissenberg no.) Wi; however, the onset value varies from pore to pore. This observation that single pores exposed to the same macroscopic flow rate become unstable in different ways provides a fascinating pore-scale analog of “molecular individualism” [P.  De Gennes, Molecular individualism. Science 276, 1999–2000 (1997)], in which single polymers exposed to the same extensional flow elongate in different ways; the authors therefore termed it “porous individualism”, although it is important to note that here, this effect is still at the continuum (not molecular) scale. Thus, unstable flow is spatially heterogeneous across the different pores of the medium, with unstable and laminar regions coexisting >>

AA << quantitatively established that the energy dissipated by unstable pore-scale fluctuations generates an anomalous increase in flow resistance through the entire medium that agrees well with macroscopic pressure drop measurements. >>

Sujit S. Datta, Arezoo M. Ardekani, et al. Perspectives on viscoelastic flow instabilities and elastic turbulence. arXiv: 2108.09841v1 [physics.flu-dyn]. Aug 22, 2021. 

https://arxiv.org/abs/2108.09841

Also

keyword 'transition' | 'transitional' in FonT

https://flashontrack.blogspot.com/search?q=transition

https://flashontrack.blogspot.com/search?q=transitional

keyword 'transition' | 'transizion*' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=transition

https://inkpi.blogspot.com/search?q=transizione

https://inkpi.blogspot.com/search?q=transizioni

keywords: gst, droplet, fluctuations, disorder, instability, viscoelastic flow instability, turbulence, elastic turbulence, individualism, porous individualism, transition

# gst: concerning turbulences, turbulence researchers & lovers ...

<< Charles Doering, a mathematical physicist at the University of Michigan in Ann Arbor, says he hopes that the approach might ultimately point the way to a model of turbulence that is simpler to use than the Navier–Stokes equations, and works in all situations. That is the “grand dream”, he says >>

Davide Castelvecchi. Mysteries of turbulence unravelled. Simulations follow how swirls in a fluid transfer and dissipate energy. Aug 21, 2017 Corrected: Aug 22, 2017

http://www.nature.com/news/mysteries-of-turbulence-unravelled-1.22474

FonT

"a model of turbulence that is simpler to use (..) and works in all situations"; una intelligenza artificiale, anche genericamente  di "media forza" sara' senz'altro in totale accordo con Charles Doering.

# gst: apropos of turbulence, self-similarity of turbulent flows with internal and external intermittency

<< Scientists have long used supercomputers to better understand how turbulent flows behave under a variety of conditions. Researchers have now include the complex but essential concept of 'intermittency' in turbulent flows. >>️

<< Despite its seemingly random, chaotic characteristics, researchers have identified some important properties that are universal, or at least very common, for turbulence under specific conditions. (..) Much of that important turbulent motion may stem from what happens in a thin area near the edge of the flame, where its chaotic motions collide with the smoother-flowing fluids around it. This area, the turbulent-non-turbulent interface (TNTI), has big implications for understanding turbulent mixing. >>️

<< Scientists distinguish between internal intermittency, which occurs at the smallest scales and is a characteristic feature of any fully developed turbulent flow, and external intermittency, which manifests itself at the edge of the flame and depends on the structure of the TNTI. >>️

<< For Bode and Gauding (Mathis Bode, Michael Gauding), understanding the small-scale turbulence happening at the thin boundary of the flame is the point. >>

<< Our simulations are highly resolved and are interested in these thin layers, (..) For production runs, the simulation resolution is significantly higher compared to similar DNS (direct numerical simulations ) to accurately resolve the strong bursts that are connected to intermittency. >> Mathis Bode. 

️

Simulations of turbulence's smallest structures. Gauss Centre for Supercomputing. Jul 8, 2021. 

https://www.sciencedaily.com/releases/2021/07/210708103609.htm

<< In turbulent jet flows, the phenomenon of external intermittency originates from a sharp layer, known as the turbulent/ non-turbulent interface, that separates the turbulent core from the surrounding irrotational fluid. First, it is shown that low-order and higher-order structure functions in both the core and the shear layer of the jet satisfy complete self-preservation, which means that structure functions are invariant with time and collapse over the entire range of scales, regardless of the set of length and velocity scales used for normalization. Next, the impact of external intermittency on small-scale turbulence is studied along the cross-wise direction by the self-similarity of structure functions. It is shown that structure functions exhibit from the centre toward the edge of the flow a growing departure from self-similarity and the prediction of classical scaling theories. By analysing statistics conditioned on the turbulent portion of the jet, it is demonstrated that this departure is primarily due to external intermittency and the associated similarity-breaking effect. >>️

Michael Gauding, Mathis Bode, et al. Self-similarity of turbulent jet flows with internal and external intermittency. Journal of Fluid Mechanics.  919 , 25, A41. doi: 10.1017/ jfm.2021.399. Jun 1,  2021.

https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/abs/selfsimilarity-of-turbulent-jet-flows-with-internal-and-external-intermittency/170B9415870F47A94D041FEE7E904840

Michael Gauding, Mathis Bode, et al. On the combined effect of internal and external intermittency in turbulent non-premixed jet flames. Proceedings of the Combustion Institute. 38, (2): 2767-2774. doi: 10.1016/ j.proci.2020.08.022. Dec 9, 2020.

https://www.sciencedirect.com/science/article/abs/pii/S1540748920306064

keyword 'Intermittency' in ScienceDirect

https://www.sciencedirect.com/topics/engineering/intermittency

Also

1939 - stocastici accessi (di traslitteranti ludi). Notes. Jan 11, 2006. 

(quasi-stochastic poetry )

https://inkpi.blogspot.com/2006/01/1939-stocastici-accessi-di.html

2064 - on responses to deviant stimuli.

Notes. Sep 26, 2006. (quasi-stochastic poetry )

https://inkpi.blogspot.com/2006/09/2064-on-responses-to-deviant-stimuli.html

# gst: apropos of transitions, three distinct new families of long-wave instabilities and potential new pathways to turbulence.

AA << reveal three previously unknown instabilities, distinct from the well-known Kelvin-Helmholtz Instability (KHI) and Holmboe Wave Instability (HWI), in that they have longer wavelengths (..) and often slower growth rates. >>

<< The circumstances under which turbulence can persist in strongly stratified flows remains a fascinating debate within the community. [AA] demonstrated that weakly unstable (very) long waves may trigger turbulence and mixing after long periods of time, even under initially very strongly stratified conditions. >>

Lu Zhu, Amir Atoufi, Adrien Lefauve, Rich R. Kerswell, P. F. Linden. Long-wave instabilities of sloping stratified exchange flows. arXiv:2309.10056v1 [physics.flu-dyn]. Sep 18, 2023.

https://doi.org/10.48550/arXiv.2309.10056

Also: waves, instability, transition, turbulence, chaos, in https://www.inkgmr.net/kwrds.html

Keywords: gst, waves, instability, long-wave instability, transition, turbulence, chaos

# gst: apropos of transitions, two aspects of intermittency

<< intermittency produces significant probability of rare events that may locally accelerate the collision rates by a large factor in comparison with estimates using typical events. >>

<< Increasing intermittency of turbulence destroys the theory not via stronger bursts, but rather via increase of characteristic sizes of regions of calm and quiescent flow. ([AA️] remind that these two aspects of intermittency go together: increase of regions of calm flow and at the same time increased probability of strong bursts ([8] U. Frisch, Turbulence: The Legacy of A. N. Kolmogorov, (Cambridge University Press, New York, 1995).). >>

Itzhak Fouxon, Seulgi Lee, Changhoon Lee. Intermittency and collisions of fast sedimenting droplets in turbulence.  arXiv:2205.06972v1 [physics.flu-dyn]. May 14, 2022. 

https://arxiv.org/abs/2205.06972

Also

keyword 'intermittency' in FonT

https://flashontrack.blogspot.com/search?q=intermittency

keyword 'intermittenza|e' | 'intermittente|i' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=intermittenza

https://inkpi.blogspot.com/search?q=intermittenze

https://inkpi.blogspot.com/search?q=intermittente

https://inkpi.blogspot.com/search?q=intermittenti

Keywords: gst, intermittency, collision, drop, droplet, turbulence

# gst: the role of turbulence in the formation of self-organizing patterns

<< What part of the 'self' is responsible for the 'organization?' That role is performed by the unstable modes ('control modes') which alter the position and stability of the local equilibria that drive the time-evolution of the system >> Jacob Halatek

<< These turbulences (..) do not result in the complete loss of order (..) precisely the opposite occurs. When we destabilize the system, we observe that turbulence develops relatively rapidly. But upon further perturbation, the system undergoes a transition in which it is far from equilibrium, but nevertheless clearly ordered and non-turbulent >> Erwin Frey

Ludwig Maximilian University of Munich. Pattern formation - the paradoxical role of turbulence.
Feb 19, 2018.

https://m.phys.org/news/2018-02-pattern-formationthe-paradoxical-role-turbulence.html  

Jacob Halatek, Erwin Frey. Rethinking pattern formation in reaction- diffusion systems. Nature Physics. doi: 10.1038/s41567-017-0040-5. Feb 19, 2018.

https://www.nature.com/articles/s41567-017-0040-5

# gst: nematic order condensation and topological defects in inertial active nematics

<< Living materials at different length scales manifest active nematic features such as orientational order, nematic topological defects, and active nematic turbulence. Using numerical simulations (AA) investigate the impact of fluid inertia on the collective pattern formation in active nematics. >>️

<< an incremental increase in inertial effects due to reduced viscosity results in gradual melting of nematic order with an increase in topological defect density before a discontinuous transition to a vortex-condensate state. The emergent vortex-condensate state at low enough viscosities coincides with nematic order condensation within the giant vortices and the drop in the density of topological defects. (AA) further show flow field around topological defects is substantially affected by inertial effects. (..) no evidence of universal scaling at higher viscosities. >>

️

Roozbeh Saghatchi, Mehmet Yildiz, Amin Doostmohammadi. Nematic order condensation and topological defects in inertial active nematics. Phys. Rev. E 106, 014705. July 25, 2022.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.106.014705

Also: 'turbulence', 'vortex', 'defect', 'drop' in https://www.inkgmr.net/kwrds.html

Keywords: gst, behavior, collective behavior, patterns, turbulence, nematic turbulence, viscosity, vortex, defect, drop

# gst art: an image of chaotic hydrodynamics, by "Leo"

<< One of the first to visualize these flows was scientist, artist, and engineer Leonardo da Vinci, who combined keen observational skills with unparalleled artistic talent to catalog turbulent flow phenomena. Back in 1509, Leonardo was not merely drawing pictures. He was attempting to capture the essence of nature through systematic observation and description. In this figure,  https://cdn.arstechnica.net/wp-content/uploads/2018/10/daVinciWake.png   we see one of his studies of wake turbulence, the development of a region of chaotic flow as water streams past an obstacle. >>

Lee Phillips. Turbulence, the oldest unsolved problem in physics. The flow of water through a pipe is still in many ways an unsolved problem. Oct 10, 2018.

https://arstechnica.com/science/2018/10/turbulence-the-oldest-unsolved-problem-in-physics/

# gst: the effects of order- disorder on a system of swarmalators that move on a one-dimensional ring.

<< Swarmalators are phase oscillators that cluster in space, like fireflies flashing on a swarm to attract mates. >>

<< In this work, (AA) explore the effects of disorder induced by phase frustration on a system of Swarmalators that move on a one-dimensional ring. >>

They find << numerically and analytically, the ordered and disordered states that emerge in the system. The active states, not present in the model without disorder, resemble states found previously in numerical studies for the 2D Swarmalators system. One of these states, in particular, shows similarities to turbulence generated in a flattened media. (AA) show that all ordered states can be generated for any values of the coupling constants by tuning the phase frustration parameters only. Moreover, many of these combinations display multi-stability. >>️

Joao U.F. Lizarraga, Marcus A.M. de Aguiar. Sakaguchi Swarmalators. arXiv: 2305.08615v1 [nlin.PS]. May 15, 2023. 

https://arxiv.org/abs/2305.08615

Also:  'swarm', 'turbulence', 'noise', 'particle' in: https://www.inkgmr.net/kwrds.html

Keywords: gst, swarm, turbulence, noise, particle

# gst: pattern generation through turbulent cascades

<< Fully developed turbulence is a universal and scale-invariant chaotic state characterized by an energy cascade from large to small scales where the cascade is eventually arrested by dissipation. In this Letter, (AA) show how to harness these seemingly structureless turbulent cascades to generate patterns. Conceptually, pattern or structure formation entails a process of wavelength selection: patterns typically arise from the linear instability of a homogeneous state. By contrast, the mechanism (they) propose here is fully non-linear and triggered by a non-dissipative arrest of turbulent cascades. Instead of being dissipated, energy piles up at intermediate scales. Using a combination of theory and large-scale simulations, (AA) show that the tunable wavelength of these cascade-induced patterns is set by a non-dissipative transport coefficient called odd or gyro viscosity. This non-dissipative viscosity is ubiquitous in chiral systems (..). Beyond chiral fluids, cascade-induced pattern formation could occur in natural systems (..) as well as in industrial processes (..). >>

Xander M. de Wit, Michel Fruchart, et al. Pattern formation by non-dissipative arrest of turbulent cascades. arXiv: 2304.10444v1 [cond-mat.soft]. Apr 20, 2023.

https://arxiv.org/abs/2304.10444

Also: 'turbulence', 'vortex', 'game', 'evolution', 'ai' in https://www.inkgmr.net/kwrds.html

Keywords: gst, vortex, vorticity,  turbulence, turbulent cascade, pattern formation, game, evolution, ai (artificial intelligence)

# gst: complex flows by hairpin vortices behind hills with different scales

 << In the flow around protuberance, separation bubbles occur ahead and behind the protuberance, and a coherent vortex structure exists in the wake. In such a flow field, heat, substance, and momentum are actively transported by the vortex. (..) When multiple protuberances are set in the flow, the wakes of the protuberances interfere with each other, resulting in complicated flows. >> 

 << This study performed a numerical analysis of the hairpin vortex and heat transport generated by the interference of the wakes behind two hills in a laminar boundary layer. In the case of hills with the same scale, the interference between hairpin vortices in the wake is more intensive than in the different-scale hills. When the hills with different scales are installed, hairpin vortices with different scales are periodically shed. >> 

 

  << Regardless of the scale ratio of the hills, when the hill spacing in the spanwise direction is narrowed, the asymmetry of the hairpin vortex in the wake increases due to the interference between the wakes. At this time, the turbulence caused by the leg and the horn-shaped secondary vortex on the spanwise center side in the hairpin vortex increases, and heat transport around the hairpin vortex becomes active. >> 

 

Hideki Yanaoka, Tatsuya Hamada. Hairpin vortices and heat transfer in the wakes behind two hills with different scales. arXiv: 2306.17365v1 [physics.flu-dyn]. Jun 30, 2023. 

https://arxiv.org/abs/2306.17365

Also: vortex, turbulence in https://www.inkgmr.net/kwrds.html

Keywords: gst, vortex, hairpin vortex, turbulence

# gst: complex flow patterns generated by swarms of bubbles

<< When swarms of bubbles are driven upwards through a fluid by their buoyancy, they can generate complex flow patterns in their wake. Named 'pseudo-turbulence,' these patterns are characterized by a universal mathematical relationship between the energy of flows of different sizes, and the frequency of their occurrence. This relationship has now been widely observed through 3-D simulations, but it is less clear whether it would still hold for 2-D swarms of bubbles. >>

AA << show that in 2-D simulated fluids, this pattern changes within larger-scale flows in less viscous fluids. (..) In the past, many studies of pseudo-turbulence have found the statistical properties of 3-D bubble swarms remain universal over a wide range of bubble surface tensions, fluid viscosities, and density ratios between bubbles and fluids. In 2-D fluids, however, an effect named an 'inverse energy cascade' enables energy to be transferred from small- to large-scale flows. >>

Characterising complex flows in 2-D bubble swarms. Springer. Dec 4, 2020

https://phys.org/news/2020-12-characterising-complex-d-swarms.html

Rashmi Ramadugu, Vikash Pandey, Prasad Perlekar. Pseudo-turbulence in two-dimensional buoyancy-driven bubbly flows: A DNS study. The European Physical Journal E. V 43, no. 73. doi: 10.1140/ epje/i2020-11997-0. Nov 25, 2020.

https://link.springer.com/article/10.1140/epje/i2020-11997-0

Also

keyword 'bubble' in FonT

https://flashontrack.blogspot.com/search?q=bubble