# gst: porous substrates and foams on the structure of turbulent boundary layers over them.

<< Turbulent flow over and past porous surfaces is encountered in many engineering problems, ranging from flow over forest canopies (..) to flows over and past river beds (..). This makes the understanding or the flow behaviour over porous surfaces crucial. >>

️

<< The present study shows that transition from thick to thin substrate flow behavior depends not only on thickness-to-pore ratio (..) but also on substrate density relative to viscous scales of the flow. >>️

Prateek Jaiswal, Bharathram Ganapathisubramani. Effects of porous substrates on the structure of turbulent boundary layers. arXiv: 2301.04102v1 [physics.flu-dyn]. Jan 10, 2023.

https://arxiv.org/abs/2301.04102

Also

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

Keywords: gst, turbulence, turbulent layers, porosity, porous substrates, foam

# gst: stagnation points controlling the onset and strength of chaotic fluctuations (in viscoelastic porous media flows)

<< Viscoelastic porous media flows become chaotic beyond critical flow conditions, impacting processes including enhanced oil recovery and targeted drug delivery. Understanding how geometric details of the porous medium affect the onset and strength of the chaotic flows can lead to fundamental insights and potential optimization of such processes. Recently, it has been argued that geometric disorder in the medium suppresses chaotic fluctuations. In contrast, (AA) demonstrate that disorder can also significantly enhance fluctuations given a different originally ordered configuration. (AA) show that the occurrence of stagnation points in the flow field is the vital factor controlling the onset and strength of fluctuation, providing a general and intuitive understanding of how pore geometry affects this important class of complex viscoelastic flows. >>

Simon J. Haward, Cameron C. Hopkins, Amy Q. Shen. Stagnation points control chaotic fluctuations in viscoelastic porous media flow. PNAS. 118 (38)  e2111651118. doi: 10.1073/ pnas.2111651118. Sep 21, 2021. 

https://www.pnas.org/content/118/38/e2111651118

https://twitter.com/ShenU_OIST/status/1438306244998033408

Also

keyword 'elastic' | 'turbulence' | 'disorder' in FonT

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

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

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

keyword 'elastico' | 'turbolento' | 'disordine' in Notes

(quasi-stochastic poetry)

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

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

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

keywords: viscoelastic flows, porous media, stagnation, elastic turbulence, chaos, chaotic fluctuations, geometric disorder.

# gst: pulsating active matter.

<< the mechanical pulsation of locally synchronized particles is a generic route to propagate deformation waves. >>

️

AA << consider a model of dense repulsive particles whose activity drives periodic change in size of each individual. >>️

They << show that the competition between repulsion and synchronization triggers an instability which promotes a wealth of dynamical patterns, ranging from spiral waves to defect turbulence. >>️

Yiwei Zhang, Etienne Fodor. Pulsating Active Matter. Phys. Rev. Lett. 131, 238302. Dec 8, 2023. 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.238302

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

Keywords: gst, waves, particle, transition, instability, turbulence

# gst: apropos of collisions of a vortex dipoles, vortex unbinding, vortex pinning to the edge, and emission of rarefaction pulses.

<< Vortices and dark solitons are fundamental defects that appear in nonlinear physics at all scales, from nonlinear optics to cosmic fluids. In two or three dimensions, dark solitons are fundamentally connected to highly ordered vortex states through an intrinsic modulation instability in the surrounding matter. >>️

<< Here, [AA] report an experimental realization of ring dark soliton (RDS)  generation in a two-dimensional atomic superfluid trapped in a circular box. By quenching the confining box potential, [they] observe an RDS emitted from the edge and its peculiar signature in the radial motion. As an RDS evolves, [they] observe transverse modulations at discrete azimuthal angles, which clearly result in a patterned formation of a circular vortex dipole array. Through collisions of the vortex dipoles with the box trap, [they] observe vortex unbinding, vortex pinning to the edge, and emission of rarefaction pulses. >>

Hikaru Tamura, Cheng-An Chen, Chen-Lung Hung. Observation of Self-Patterned Defect Formation in Atomic Superfluids–from Ring Dark Solitons to Vortex Dipole Necklaces. Phys. Rev. X 13, 031029. Sep 14, 2023. 

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.13.031029

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

Keywords: gst, soliton, dark soliton, vortex, turbulence, waves. 

# life: declining towards turbulence, thus ecstatic (detotuthec)

(1/3) for our birthdays on July 11th (*1th) and July 25th (*9th) ... forever Nomads (*), curious, young.  

https://www.inkgmr.net   https://www.inkgmr.net/tammi

@flashontrack  11:36 11lug21

https://twitter.com/flashontrack/status/1414156586889748482

(2/3) (*) e.g. exotic, maverick, agnostic,  track seeker, meta-mechanic pulsating manipulator, ockhamistic, erratic, chaotic, #detotuthec (declining towards turbulence, thus ecstatic), ab-normal ...

@flashontrack 11:37 11lug21

https://twitter.com/flashontrack/status/1414156987240173569

(3/3) with mindfulness, compassion and tenacity, where also vengeance consists in (try) saving others (whatever 'others' means).

@flashontrack 11:38 11lug21

https://twitter.com/flashontrack/status/1414157124318507008

Keywords: detotutech, detect thou

# gst: more on turbulence under rotation, by Biferale, Bonaccorso, Lanotte, et al.

AA << study turbulence under rotation in the presence of simultaneous direct and inverse cascades >>

AA << quantify (..) the effects of those coherent vertical structures on the preferential concentration of light and heavy particles >>

<< Rotating, turbulent flows are ubiquitous in nature >>

Biferale L, Bonaccorso F,  Lanotte AS, et al.  Coherent Structures and Extreme Events in Rotating Multiphase Turbulent Flows. Phys. Rev. X 6, 041036 doi: 10.1103/PhysRevX.6.041036  Nov 21, 2016

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.6.041036

<< What can you find in the air, on an aeroplane, or even deep inside your heart? No, the answer isn’t love. It is, of course, turbulent flow >>

In a spin: studying turbulent flow under rotation. Nov 5, 2017

http://www.prace-ri.eu/spin-studying-turbulent-flow-rotation/

https://www.sciencedaily.com/releases/2017/11/171106100301.htm

# gst: small-scale random perturbations, Arnold's cat spontaneously stochastic

<< Multi-scale systems (..) may possess a fascinating property of spontaneous stochasticity: a small-scale initial uncertainty develops into a randomly chosen largescale state in a finite time, and this behavior is not sensitive to the nature and magnitude of uncertainty (..). >>

A << intriguing form is the Eulerian spontaneous stochasticity (ESS) of the velocity field itself: an infinitesimal small-scale noise triggers stochastic evolution of velocity field at finite scales and times. >>

AA << prove that a formally deterministic system with scaling symmetry yields a stochastic process with Markovian properties if it is regularized with a vanishing small-scale random perturbation. Besides its significance for understanding turbulence, (their) model extends the phenomenon of ESS beyond the scope of fluid dynamics: (AA) discuss a prototype of a feasible experiment for observing ESS in optics or electronics, as well as potential applications in other physical systems.>>

Alexei A. Mailybaev, Artem Raibekas. Spontaneously stochastic Arnold's cat. arXiv:2111.03666v1 [nlin.CD]. Nov 5,  2021.

https://arxiv.org/abs/2111.03666

keywords: gst, Arnold's cat, randomness, stochasticity, spontaneous stochasticity, small-scale random perturbations, noise, turbulence, chaos 

# gst: streak-vortex instabilities in heterogeneous turbulent boundary layers

AA << re-examine the turbulent boundary layers developing over surfaces with spanwise heterogeneous roughness of various roughness wavelengths 0.32≤S/δ¯¯≤3.63, where S is the width of the roughness strips and δ¯¯ is the spanwise-averaged boundary-layer thickness. >>

<< The heterogeneous cases induce counter-rotating secondary flows, and these are compared to the large-scale turbulent structures that occur naturally over the smooth wall. Both appear as meandering elongated high- and low-momentum streaks in the instantaneous flow field. >>

<< Results suggest that the secondary flows might be spanwise-locked turbulent structures, with S/δ¯¯ governing the strength of the turbulent structures and possibly the efficacy of the surface in locking the structures in place (most effective when S/δ¯¯≈1). >>

<< Conditional averages of the fluctuating velocity fields of both spanwise heterogeneous and smooth wall cases result in structures that are strongly reminiscent of the streak-vortex instability model. (proposed in Jeong et al.,1997) >>

<< One outstanding question that remains unanswered in the present study is the cause of the prominent meandering of the turbulent structures, which is only observed when S/δ¯¯≈1 >>️️

️

Dea Daniella Wangsawijaya, Nicholas Hutchins. Investigation of unsteady secondary flows and large-scale turbulence in heterogeneous turbulent boundary layers. arXiv: 2110.02268v1 [physics.flu-dyn]. Oct 5, 2021.

https://arxiv.org/abs/2110.02268

keywords: gst, fluid dynamics, vortices, vortex instability, streak-vortex instability,  roughness, heterogeneous roughness, turbulence, turbulent boundary layers.

# s-gst: like a rolling stone

<< Here we report the discovery that even the simplest, oldest and most prevalent forms of evolutionary movement—rolling bodies and whirls of turbulence—exhibit the same body-size effect on life time and life travel as the evolutionary movement united by the body-size effect so far: animals, rivers, vehicles, jets and plumes. >>

Adrian Bejan. Rolling stones and turbulent eddies: why the bigger live longer and travel farther. Nature. Scientific Reports 6, Article number: 21445 (2016). doi:10.1038/srep21445. Published online: 17 Feb 2016.

http://www.nature.com/articles/srep21445

http://pratt.duke.edu/news/rolling-stones-turbulence-connect-evolution-physics

more:

Muddy Waters. Rollin' Stone

https://m.youtube.com/watch?v=sVmEMv8rcCA

Bob Dylan. Like a Rolling Stone (Original)

https://m.youtube.com/watch?v=H3Kt2v-PN9A

# gst: apropos of turbulences close to a wall, the repetitive structure of a vortex

<< At the boundary where a fluid flows over a fixed structure, a turbulent boundary layer is created where the fluid interacts with the wall, creating eddies in the current. These eddies may seem to be random on first glance, but they actually create distinct patterns, with countless tiny eddies close to the wall; fewer but larger eddies located a little farther out; and even fewer, but still larger, eddies beyond those. >>

<< "We knew that, underlying these very complicated structures, there had to be a very simple pattern. We just didn't know what that pattern was until now," says McKeon, who next plans to dig deeper into the model to quantify just how many eddies should be included to create an accurate representation of the whole. >>

Engineers exploit the repeating structure of turbulence to create a more complete model of the phenomenon. California Institute of Technology. Nov 6, 2019.

https://m.phys.org/news/2019-11-exploit-turbulence-phenomenon.html

Beverley J. McKeon. Self-similar hierarchies and attached eddies. Phys. Rev. Fluids 4, 082601(R). Aug 26, 2019.

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.4.082601

# gst: laminar and turbulent flows detected in music, a fluid framework approach

<< The relationship between musical material and physical phenomena has become a topic in the musicological literature over the last several decades, particularly concerning elements of the musical system itself, and constructions found in the work of contemporary classical composers such as Gyorgy Ligeti and Iannis Xenakis. Most scholars, who adopt this approach, explore the physical phenomena of fractals in the analysis of musical works, but fluid mechanical frameworks, such as laminar and turbulent flows, offer a new avenue to be explored. In this paper (AA) will propose a novel method of musical analysis for examining musical structures in terms of fluid-like behaviour such that Ligeti etude no. 9 serves as a model, whereby the metaphors of laminar and turbulent flows take precedence. >>

Noah Chuipka. Musico-acoustic Depictions of Laminar and Turbulent Flows in Ligeti Piano Etude No. 9 and a Novel Method of Analysis. arXiv: 2306.10093v1 [cs.SD]. Jun 17, 2023. 

https://arxiv.org/abs/2306.10093

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

Keywords: gst, music, jazz, turbulence

# gst: when randomly-timed external impulses can synchronize

<< Random perturbations applied in tandem to an ensemble of objects can synchronize their motion. (AA) study multiple copies of an object in periodic motion such as a firing neuron, each with an arbitrary phase. Randomly-timed external impulses can synchronize these phases. For impulses slightly too strong to synchronize, (they) find remarkable erratic synchronization, with stochastic fluctuations from near-perfect to more random synchronization. The sampled entropies of these phase distributions themselves form a steady-state ensemble. A stochastic dynamics model for the entropy's evolution accounts for the observed exponential distribution of entropies and the stochastic synchronization. >>

<< One general virtue of noise-induced synchronization is that one may use it to induce synchronization without

specific knowledge about the limit cycle being synchronized, such as the phase map function or the cycle time.(..) As noted in the Introduction, synchronization of a remote oscillator enables transmission of information.

Stochastic synchronization appears to have comparable ability, potentially useable by technology or biology. >>️

<< The stochastic synchronization phenomenon explored above seems to be a distinctive mode of organization. It can be produced via broad classes of driving, and creates striking fluctuations of randomness. This model may aid understanding of other puzzling systems showing erratic fluctuations, such as strong turbulence. >>️

️

Yunxiang Song, Thomas A. Witten. Stochastic synchronization induced by noise. arXiv:2108.13172v1 [cond-mat.stat-mech]. Aug 16, 2021.

https://arxiv.org/abs/2108.13172

Also

<< stabilizzare il volo del fascio di aquiloni  >> in: ️2149 - onda di predazione (to knock seals off the ice).  Notes. Dec 17, 2007. (quasi-stochastic poetry)

https://inkpi.blogspot.com/2007/12/2149-onda-di-predazione-to-knock-seals.html

keyword 'noise' | 'fuzzy' in FonT

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

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

# gst: towards the characterization of lines, links, writhes and twists in a vortex.

<< Vorticity in turbulent flows is often organized into complex geometries that influence the dynamics. (AA) use a relatively novel approach to describe these geometries: that of obtaining segments of vortex lines embedded in the flow. This enables to quantify the geometric features of these objects. >>

<< Vortex lines differ widely in their behaviour but (AA) find some unifying features. The decay from high levels of vorticity is shown to happen over a short fraction of the vortex length. The local curvature is inversely related with the vorticity magnitude. Strong parts of vortex lines bundle together. >>

Saumav Kapoor, Rama Govindarajan, Siddhartha Mukherjee. Geometric characterization of vortex lines in turbulence. arXiv: 2301.06808v1 [physics.flu-dyn]. Jan 17, 2023.

https://arxiv.org/abs/2301.06808

Also

keyword 'vortex' in FonT

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

keyword 'vortice' in Notes

 (quasi-stochastic poetry)

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

Keywords: gst, vortex, vortices, vortexes, vorticity

# behav: Calanoid copepods swim freely and jump in turbulence

AA << provide evidence for an active adaptation that allows these small organisms [Calanoid copepods] to adjust their motility in response to background flow >>

Francois-Gael Michalec, Itzhak Fouxon, et al. Zooplankton can actively adjust their motility to turbulent flow. PNAS. doi:10.1073/pnas.1708888114

http://m.pnas.org/content/early/2017/12/05/1708888114

<< These jumps enable the plankton to hunt their prey and the males to catch a female >> Markus Holzner.

Plankton swim against the current.
Dec 12, 2017.

https://m.phys.org/news/2017-12-plankton-current.html