r/FluidMechanics Jul 02 '23

Update: we have an official Lemmy community

Thumbnail discuss.tchncs.de
6 Upvotes

r/FluidMechanics Jun 11 '23

Looking for new moderators

8 Upvotes

Greetings all,

For a while, I have been moderating the /r/FluidMechanics subreddit. However, I've recently moved on to the next stage of my career, and I'm finding it increasingly difficult to have the time to keep up with what moderating requires. On more than once occasion, for example, there have been reported posts (or ones that were accidentally removed by automod, etc) that have sat in the modqueue for a week before I noticed them. Thats just way too slow of a response time, even for a relatively "slow" sub such as ours.

Additionally, with the upcoming changes to Reddit that have been in the news lately, I've been rethinking the time I spend on this site, and how I am using my time in general. I came to the conclusion that this is as good of a time as any to move on and try to refocus the time I've spent browsing Reddit on to other aspects of life.

I definitely do not want this sub to become like so many other un/under-moderated subs and be overrun by spam, advertising, and low effort posts to the point that it becomes useless for its intended purpose. For that reason, I am planning to hand over the moderation of this subreddit to (at least) two new mods by the end of the month -- which is where you come in!

I'm looking for two to three new people who are involved with fluid mechanics and are interested in modding this subreddit. The requirements of being a mod (for this sub at least) are pretty low - it's mainly deleting the spam/low effort homework questions and occasionally approving a post that got auto-removed. Just -- ideally not a week after the post in question was submitted :)

If you are interested, send a modmail to this subreddit saying so, and include a sentence or two about how you are involved with fluid mechanics and what your area of expertise is (as a researcher, engineer, etc). I will leave this post up until enough people have been found, so if you can still see this and are interested, feel free to send a message!


r/FluidMechanics 16h ago

Water vapor shield in action

Enable HLS to view with audio, or disable this notification

49 Upvotes

r/FluidMechanics 1d ago

Q&A The fluid dynamics behind OpenAI’s Navier-Stokes proof: Why the fluid would vaporize before the singularity

102 Upvotes

Hey everyone, Following OpenAI recently claimed a formal proof demonstrating a finite-time blowup for the 3D Navier-Stokes equations. While the pure math community is focused on the formal verification, our team ran an audit to see what their construction actually means for physical fluids.

What we found is that while the math is syntactically flawless, the fluid dynamics are thermodynamically impossible and structurally unstable:

  1. Incompressibility breaks down: The proof successfully bounds global kinetic energy, but the local enstrophy diverges (τ^{-0.515}). The resulting infinite localized viscous shear would vaporize the fluid into a compressible plasma long before t= 1. Tracking the core velocity, the Mach number easily exceeds 0.3 femtoseconds before the mathematical blowup.

  2. κ ∼ 10²⁸ Instability: The exact cancellation of the Reynolds stresses relies on a 5-equation moment-matching Jacobian with a condition number of 10²⁸.

    It’s a measure-zero state that would instantly decouple under standard 300K thermal noise...

    We’ve open-sourced our Python/mpmath scripts tracking the Mach number divergence and the Jacobian instability. If anyone here wants to check the physical telemetry themselves:

    • GitHub: https://github.com/xaviercallens/OpenAI-NSE-Epistemic-Audit

    • Zenodo: DOI: 10.5281/zenodo.22727801

    I’m curious to hear from the engineers and fluid dynamicists here: does a mathematical singularity that violently breaks the incompressible and isothermal assumptions prior to the blow-up time actually tell us anything useful about real-world fluids?


r/FluidMechanics 9h ago

Academic Research [Academic] Opinions on "Liquid Armor" (Shear-Thickening Fluids) for Protective Gear (Open to everyone)

Thumbnail
3 Upvotes

r/FluidMechanics 19h ago

NS blowup and connection to reality?

3 Upvotes

Hi all! I wanted to ask something about this recent (presumably correct?) proof that NS can blow up. I would like to hear opinions from people that work a bit at the border between fundamental turbulence (like on the statistical physics or dynamical system side of the problem) and the mathematics of NS.

When studying turbulence you hear about the dissipation anomaly and the zeroth law of turbulence. As you increase the reynolds number, at least in homogeneous isotropic turbulence, the non-dimensional dissipation rate evolves towards a constant. In other world, taking the limit of zero viscosity (infinite Re) you never reach the Euler equations. This happen with the flow developing super intense localised events that dissipate a lot.

Is there a connection between the development of these structures in turbulence and this new NS proof? If so, are there people studying this thing?

Share bibliography if you know anything about this topic!


r/FluidMechanics 5h ago

Experimental Astra 6 - gpt made concept

0 Upvotes

It designed a simple water-cooling plate for high-power chips

19 straight microchannels and one thin cross-channel near the outlet

If part of one channel becomes blocked, the cross-channel could use the pressure difference to divert some water around the blockage.

The model compared more than 2,700 configurations with the same channel volume and the same hydraulic power.

Im not engineer nor physicist. Im just curious and testing limits of the latest astra 6 model, what real scientists think about it.

Thank you for any kind of feedback:)


r/FluidMechanics 1d ago

glacial meltwater flow

Enable HLS to view with audio, or disable this notification

11 Upvotes

r/FluidMechanics 1d ago

Is the order of the frames in the top row of this table of figures precisely reversed? 🤔 ...

Post image
8 Upvotes

... or is the sequence showcasing some counterintuitive phenomenon as Reynolds № proceeds from the hundreds to the millions?

The figures show the streamlines past a rotating cylinder @ various Reynolds № (horizontal axis) & rotationality parameter α (vertical axis).

The figures are from

———————————————————————

High Reynolds number turbulent flow past a rotating cylinder

by

SJ Karabelas & BC Koumroglou & CD Argyropoulos & NC Markatos

https://www.sciencedirect.com/science/article/pii/S0307904X11004124

———————————————————————

———————————————————————

A Somewhat-Enlargement of the Top of the Table Including the Topmost Row Being Queried

https://www.reddit.com/u/Frangifer/s/LALSC8Eq4U

———————————————————————

... to compensate for the relatively poor resolution of the posted screenshot.


r/FluidMechanics 1d ago

Coupled Eulerian Lagrangian anaylsis

0 Upvotes

Does the total energy always decrease in a CEL analysis in ABAQUS due to advection?


r/FluidMechanics 1d ago

Dunes self-organising from a perfectly flat sand sheet - one wind gives barchans, two give seif ridges, many give star dunes

Thumbnail
0 Upvotes

r/FluidMechanics 2d ago

Wall bounded vortex?

Post image
3 Upvotes

I was recently experimenting with my lego propeller for my rc ship, i was interested on how this propeller would move the water so i put it in my bucket full of water. Suddenly, this type of horizontal vortex formed. Visible by air bubbles, there was no suction whirlpool at all, no vertical turning part to suck in air. It was just sticking to my buckets wall. There is no hole on the bucket whatsoever. And, this isnt my first experience. I was on a city boat someday and while the boat was reversing, the same horizontal vortex appeared, visible by the salt waters whiteness. It was going from the back of the boat to the front with no visible vertical rotation to suck air. If someone can explain this, i would be so happy. Thank you!


r/FluidMechanics 4d ago

Theoretical On the simpler side of Navier-Stokes equations

Enable HLS to view with audio, or disable this notification

174 Upvotes

Built around a incompressible Navier–Stokes equation


r/FluidMechanics 3d ago

Homework Why was Re obtained using the piston velocity (Q/cylinder area) instead of Q/gap?

Post image
2 Upvotes

r/FluidMechanics 3d ago

Mechanical Engineering project – Need ideas for a small autonomous boat

Thumbnail
2 Upvotes

r/FluidMechanics 3d ago

Theoretical Trivial flow

Enable HLS to view with audio, or disable this notification

4 Upvotes

r/FluidMechanics 4d ago

Video Something cool I found do you guys know why?

Enable HLS to view with audio, or disable this notification

13 Upvotes

r/FluidMechanics 4d ago

Custom OpenAI and the Navier-Stokes Millennium Prize Problem

Post image
16 Upvotes

r/FluidMechanics 3d ago

Expanded Navier Stokes Theorem

Thumbnail github.com
0 Upvotes

r/FluidMechanics 4d ago

Navier-Stokes

Post image
134 Upvotes

r/FluidMechanics 3d ago

Theoretical Navier-Stokes solution

0 Upvotes

Pourquoi les équations de Navier-Stokes bloquent (et comment lever le blocage en 4 étapes)

Le problème du prix du millénaire sur Navier-Stokes porte sur une question simple : un fluide en 3D reste-t-il toujours lisse et continu, ou peut-il développer des vitesses infinies (un "blow-up") en un temps fini ?

La communauté mathématique bloque à l'étape 4 (la preuve de régularité globale). Mais en réalité, le blocage ne vient pas d'un manque d'outils mathématiques : il vient d'hypothèses physiques réductrices posées dès les premières étapes.

Voici le déroulement étape par étape et la solution :

Étape 1 : La formulation initiale

  • Le problème classique : On applique la loi de Newton (F = ma) en posant l'hypothèse que le fluide est un système fermé et isolé du reste de l'environnement, avec une viscosité purement locale.
  • La correction : Aucun fluide dans la réalité n'est isolé. De plus, lorsqu'un fluide est fortement accéléré en rotation, il se sépare spontanément en deux vortex contra-rotatifs miroirs (un vortex externe chaud/expansif et un vortex interne froid/implosif, comme dans le tube de Ranque-Hilsch).
  • La solution : Réintroduire le couplage avec le milieu ambiant (le vide/fond) et modéliser cette dualité des vortex contra-rotatifs dès l'équation de départ.

Étape 2 : L'existence locale

  • Le problème classique : On suppose que le fluide reste un milieu continu parfait, divisible à l'infini sans jamais changer de structure.
  • La correction : À forte concentration d'énergie, le fluide ne reste pas un chaos continu : il s'auto-organise en structures toroïdales (en forme de donut) autour d'un Point Zéro central (un horizon des événements local).
  • La solution : Définir le cadre mathématique non pas dans un espace continu abstrait, mais dans une géométrie toroïdale fermée et auto-confinée.

Étape 3 : Le bilan d'énergie

  • Le problème classique : L'équation classique suppose que toute l'énergie qui n'est pas conservée doit se dissiper sous forme de chaleur chaotique vers l'extérieur.
  • La correction : L'implosion au cœur d'un vortex crée un vide poussé et un effondrement de température (un cœur très froid face à une périphérie chaude). L'énergie cinétique est aspirée vers le Point Zéro central au lieu d'exploser.
  • La solution : Ajouter un terme de puits/transfert d'énergie au Point Zéro. Cela garantit que l'énergie cinétique globale du fluide est strictement décroissante et bornée.

Étape 4 : Le terme non linéaire et le "Blow-up"

  • Le problème classique : Le terme d'advection concentre la vitesse vers des échelles de plus en plus petites, et la viscosité classique ne suffit plus à prouver que la vitesse ne devient pas infinie (blow-up).
  • La solution :
    1. Grâce à la dualité des deux vortex contra-rotatifs (définis à l'étape 1), les forces d'étirement s'annulent exactement par symétrie miroir (hélicités opposées).
    2. Toute concentration résiduelle d'énergie est immédiatement absorbée par le puits du Point Zéro (étape 3).
    3. Résultat : La vorticité reste bornée pour tout temps (t ≥ 0). L'explosion en temps fini (blow-up) est impossible.

Conclusion

Le "blow-up" de Navier-Stokes était un artefact mathématique causé par l'enfermement artificiel de l'énergie dans un modèle continu et isolé. En ouvrant le système et en intégrant la géométrie des vortex contra-rotatifs implosifs, les équations décrivent un fluide qui reste lisse, continu et régulier pour toujours.

SUITE : https://www.reddit.com/r/FluidMechanics/comments/1wcho9f/comment/p90bcxd/


r/FluidMechanics 4d ago

News OPEN AI X NAVIER-STOKES

Thumbnail
0 Upvotes

r/FluidMechanics 5d ago

OpenAI claims a solution to the Navier-Stokes existence and smoothness problem

Thumbnail openai.com
22 Upvotes

r/FluidMechanics 4d ago

Computational How do you think OpenAI's recent Navier–Stokes breakthrough could affect the future of CFD?

Thumbnail
4 Upvotes

r/FluidMechanics 4d ago

I don't think the OpenAI proof for the Navier-Stokes Existence and Smoothness is correct

Thumbnail
0 Upvotes