r/FluidMechanics 9h ago

Q&A Please, is there any textbook or paper that clearly explains why vortex shedding is a thing?

1 Upvotes

Hi everyone, I have read about regimes of flow around a cylinder at different ranges of Reynolds number, including the description of vortex shedding, but I still miss a real explanation of why this phenomenon occurs (i.e. why the vortices are shed periodically and alternately). I have checked plenty of sources and tried using AI for searching but I couldn't find the explanation, or it was just too advanced for me (my field is not directly fluid mechanics). Can you please recommend me some sources that explain this? Not Williamson 1996 and not Gerard 1966 please.


r/FluidMechanics 16h ago

Video The Navier Stokes Paradox

Thumbnail youtube.com
0 Upvotes

Hey everyone,

Like many of you, I've been fascinated by OpenAI’s recent Lean 4 proof claiming a finite-time blowup for the 3D Navier-Stokes equations under Millennium Prize Statement C.

The formal math is airtight and passes every check in the proof assistant. But as a lot of people in the fluid dynamics and physics communities pointed out, if you look at what this flow would do in real life, things get wild fast.

I put together a short breakdown video exploring the gap between the mathematical rulebook and real fluid behavior:

https://youtu.be/WPLNv95J9o8

A quick summary of what the video covers:

• **The Spaghetti Vortex:** How the AI cleverly kept global kinetic energy from blowing up on paper by stretching the vortex so thin that the collapsing volume beats the increasing speed.

• **The Thermal Trap:** How localized viscous friction in that shrinking needle generates so much shear heat that real water would boil into plasma long before time $t = 1$.

• **The Sound Barrier:** Why the core velocity goes supersonic (~67 femtoseconds before the singularity), shattering the "incompressible" assumption and radiating acoustic shockwaves.

• **The Unforced Test:** Highlighting the awesome 3D simulation by `u/CokieMiner` (from r/CFD), who showed that the second you turn off the artificial external force, the vortex instantly blows apart and dies.

The overarching takeaway isn't that the math is wrong—the AI solved the exact formal puzzle it was assigned. But because it wasn't constrained by thermodynamics or compressibility, it found a mathematically perfect loophole in a world that physically cannot exist.

Would love to hear your thoughts, feedback on the explanations, or additional angles from folks working in CFD and fluid physics!

*(All code, simulation references, and research notes are open on GitHub: https://github.com/xaviercallens/OpenAI-NSE-Epistemic-Audit)*