Exploring the boundaries

During my experiments at the Uni, I’ve been getting some curious ink effects, which I mentioned in a recent blog entry. It seemed that my ink would sometimes be reluctant to move when placed on or near a wall of perspex; despite being in flowing water. One side of the vertical ink, that which faced oncoming horizontal flow, would remain static (the other side would drift).

Now, thanks to my colleagues’ explanations, I have a better idea of what’s happening! It seems I encountered the boundary layer effect where the ink behaves differently near a bounding surface. Yesterday, I saw it again – this time using ink in an Ahlborn tank, placed directly on glass under a slow flow of water to create streams of colour moving towards and around a cylinder. The ink seemed to stick to the bottom for a while and then form nice streams as it joined the flow. Heavier inks worked better; the lighter ones floated away too quickly.


streams of ink around a cylinder

The ink did not touch the cylinder; instead it made a clear path around it.


detail of flow past, using white and red ink. Small shedding vortices can just be seen, top right

I also set up some patterns of flow illuminated from above by neon lighting. These gave some interesting abstract, but regular patterning.


I also tried out some more Hele-shaw pictures .. my experiments went in a slightly different direction! – but I thought the results interesting enough to make a movie, which I will post soon. Meanwhile, here are some Hele-shaw fingering patterns that look like they could have self-similar features:


fractal patterning, maybe

And here are some interesting patterns made after my experimenting, when the two perspex sheets were separated:



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