Hacker News Comments on
Laminar Flow 2
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All the comments and stories posted to Hacker News that reference this video.⬐ VikingCoderHow well does this really work? It occurs to me that this could be used as a form of steganography.⬐ sparky_z⬐ gus_massaGood luck transporting it without shaking it up. Even if you leave it in place for your counterparty to find, I'd bet that diffusion would render your "message" unreadable after just a few minutes.⬐ kyberiasMaybe one could freeze it. :)Better title: "Demonstration of Reversibility of Laminar Flow"⬐ ColinWright⬐ OopsCriticalityDuly changed. Not sure it will survive, because although it's accurate and informative, it's not the title on the page. The mods may change it.⬐ semi-extrinsicNitpicking: it's not because the flow is laminar (which it is), but because it's approximately a Stokes flow.If you sit down and non-dimensionalize the Navier-Stokes equations, you end up combining viscosity, density, a representative velocity and some representative distance into what we call the Reynolds number (Re). There's two smart places you can put it, and for very slow flows that's in front of the nonlinear term. When Re << 1 you can neglect that term, and you get the Stokes equation, which is time-reversible. If you can grok what the convective derivative really means, this starts to make intuitive sense.
I said there's another place you can put the Reynolds number, and that's 1/Re in front of the viscous term. So if you have an extremely fast flow, you can neglect viscosity, which also makes intuitive sense. Such inviscid flows are the gateway into understanding turbulence.
G. I. Taylor did it better!See around the 13 minute mark: https://www.youtube.com/watch?v=51-6QCJTAjU