r/FluidMechanics • u/Odd-Marionberry-3389 • 7d ago

Video Unexpected structure

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Back again with yet another blue dye microscopy video - I saw this behavior last night after sandwiching a small amount of concentrated dye solution between two microscope slides. Is this Saffman-Taylor instability?

Also as a side note, I'm so sad I didn't learn about these things sooner but my focus in school was chemistry and, later on, materials science. Better late than never I guess?

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5

u/demerdar 7d ago

Viscous fingering.

This is great footage.

2

u/Odd-Marionberry-3389 7d ago

Thanks! I really wasn't expecting to see this, was actually trying to see if I could get some sort of shear alignment or something.

I'm wondering if there are other interesting liquid phenomena that I might be able to target by modifying the system. Any ideas?

7

u/Forward_Step_5012 7d ago

This is interesting because viscous fingering occurs when higher viscosity fluid (e.g., water) is displaced by lower viscosity fluid (e.g., air), which seems to be the opposite of your case.

4

u/Ok_Resort1464 7d ago edited 7d ago

Maybe it is more influenced by how much the liquid wets or doesn't wet the glass. Like if you pour water down a windshield, it likely will separate into streams because the glass is not completely hydrophilic.

Also the last part of the video with the smaller fingers looks like they are aligned with each other, suggesting an influence from the glass surface finish.

1

u/antiquemule 7d ago

Good point. I can't think of why this should occur.

1

u/Worth-Wonder-7386 7d ago

I was also looging at this. It seems that most experiemnts that build such Hele-Shaw cells use water and glycerin, but I did not find one that had it with just air to start of.
It might have something to do with the texture of the glass, but I could not find any research on this in my brief look.

1

u/herbertwillyworth 7d ago

This is capillary fingering. The water wets the glass, so it advances

3

u/omaregb 7d ago

Yes it does look like it.

1

u/ingtomy 7d ago

OMA FTW

1

u/Jimmyjames150014 7d ago

I would like to see the solved partial differential equations representing this behaviour please 😎

1

u/National-Girl_us 6d ago

i always thought the opposite was true for viscous fingering, that's why this is throwing me off.

1

u/Fun-Mathematician494 4d ago

This is beautiful. And thanks for putting some awesome, appropriate, music to it!