We highlight some DIW challenges related to fluid mechanics and soft matter, such as extrudability and clogging, filament stability, post-deposition spreading, slumping, and buckling. Hopefully, it will inspire various fundamental studies in fluid mechanics. (including by us)

Take‑home. Very small holes clog; below ~3 grain diameters there’s no flow, and around 3–6 it’s intermittent. Large holes act like dense, fluid‑like jets with a steady rate. This is also why hourglasses keep time so well. @univofmaryland.bsky.social @ucsbengineering.bsky.social [4/4]

Why openings matter. Near the edge, grains dilate in a thin boundary layer. This boundary layer only extends 10–15 grain diameters, but it changes the discharge rate. Once you account for it, all the data collapse onto a single curve! [3/4]

What we find. We split the flow rate in two: the speed of the grains and how they pack at the opening. Gravity and the hole size set the speed. Away from the rim, packing settles to a near‑universal “free‑fall” value. We show this with 3D experiments and DEM simulations. [2/4]

5/ Read more :

🔗 Popular science article FR : www.espci.psl.eu/fr/actualite...
🔗 Full publication in PNAS: www.pnas.org/doi/10.1073/...

And a video entry to the Gallery of Fluid Motion at the APS DFD 2023: www.youtube.com/watch?v=V0RJ...