# physics of fluids

## Water spirals are absolutely magnificent

This gif from one of the Slow mo guys videos is extremely fascinating. Water spirals have been of considerable research interest in Fluid Dynamics and as it turns out the gif is only a mode of ejection for the water.

Here are the other modes:

These are dependent on the angular velocity of the sphere The sphere is rotating clockwise with an angular velocity of (a) 84, (b) 137, © 357, and (d) 406 rad/s.

And as one keeps increasing the angular velocity, the stability of the sheet is destroyed and the fluid ejects as small droplets from the equatorial region.

Source: Langley, Kenneth & Maynes, Daniel & Truscott, Tadd. (2015). Eggs and milk: Spinning spheres partially immersed in a liquid bath. Physics of Fluids. 27. 032102. 10.1063/1.4913574.

This is awesome - Laminar flow occurs when the fluid flows in infinitesimal parallel layers with no disruption between them. In laminar flows, fluid layers slide in parallel, with no eddies, swirls or currents normal to the flow itself.

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## Surface Tension and Elasticity : A beautiful interplay

Take an elastic sheet and place a droplet on its surface while making sure that all the corners of the sheet are covered in water.

Allow this water to evaporate at room temperature and capture the time lapse. As the water volume decreases, its surface tension pulls the sheet around with it, forming these elegant patterns.

And by changing the shapes of sheets that are being used, you can alter the resultant shape. Pretty cool eh?

- Part of ‘Fluid Friday’

Source : Capillary Origami: Spontaneous Wrapping of a Droplet with an Elastic Sheet ( Contains many more illustrations and covers up the theory as well. A must read for the enthusiast )

## Beyond the Classical States of Matter

Everyone knows the 4 fundamental states of matter (solid, liquid, gas, and plasma) which are made by adding more and more energy. If we took this the other direction and took away energy making matter colder and colder we get an interesting results…

## Superfluids

Liquid helium at near absolute zero (2 Kelvin) gives a superfluid. A superfluid can, when given the slightest stir, flow forever thanks to its zero viscosity.

## Bose-Einstein Condensates

For the Helium-4 isotope in particular, at the superfluid state turns into a Bose-Einstein condensate. The matter becomes so cold that the atoms interact quantum-mechanically to form a single wavefunction.

velocity distribution data for condensate of rubidium atoms

Initial in occursum ferentur, mollia nervos fine.

## Catching prey using Vortices

I was reading about Vortices and after hours of research online, out of the blue I stumbled upon this amazing bird. This is the Red Necked Phalarope and from the looks of it seems to have put vortices to a really productive use - catching its prey.

By rotating around ~60-80 times a minute, it produces an upward vortex that sucks out insects/bugs/crustaceans from the water, which it swiftly picks up with its beak and eats. ( This one would have aced the Fluids class for sure :D)

This is analogous to tornadoes sweeping up cars and houses along its way in an upward swirl.

Mind Blown!

** The actual dynamics of vortices of course is waay more complicated. ;)

*** There are three species of phalarope (red-necked, red/grey, and Wilson’s), and they can all feed like that.

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DARQ (2019)

DARQ is a unique psychological horror game set in a zero-gravity lucid dream. The game tells the story of Lloyd, a boy who becomes aware of the fact that he is dreaming. To Lloyd’s misfortune, the dream quickly turns into a nightmare and all attempts to wake up end in failure. While exploring the darkest corners of his subconscious, Lloyd learns how to survive the nightmare by bending the laws of physics and manipulating the fluid fabric of the dream world.

What do you call nonbinary oobleck?

A non-newtonian genderfluid

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The rim above the clouds

These photos capture clouds filling almost the entire Grand Canyon due to a temperature inversion.

Cold, humid, and foggy air is denser than warm air, so if the air is stable enough it is possible for a weather pattern to form where a dense, foggy layer of air sits in the canyon and is held in place by the warmer air above it.

Recently, I read a research paper by Professor Manu Prakash from Stanford who has been working on a computer that works on fluid droplets and it is extremely fascinating.

## Manipulating Matter

Inspiration: The computers that we have at our home are capable of manipulating Information, but they cannot manipulate Physical matter per se! Ergo, build a device that could process both information and physical matter simultaneously.

The setup is actually relatively simple to understand but the working is a bit tricky. They use a ferrofluid as the droplet and control the way it behaves with a circular magnetic field.

Through the coupling of magnetic and hydrodynamic interaction forces between droplets, AND,OR,XOR,NOT and NAND logic gates, fanouts, full adder, a flip flop and a finite state machine is implemented.

If this is the sort of thing that you are interested in, I strongly recommend you read their paper.

## The bigger goal

“We already have digital computers to process information. Our goal is not to compete with electronic computers or to operate word processors on this,”

Prakash said. “Our goal is to build a completely new class of computers that can precisely control and manipulate physical matter. Imagine if when you run a set of computations that not only information is processed but physical matter is algorithmically manipulated as well. We have just made this possible at the mesoscale.”

Have a great day!

- part of ‘Fluid Friday’ series

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Ex particulis homogeneis pluma.

Trippy Cymatics
(This is not an animation, is water, led lights and vibration together)

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Particula commercium.

As an object moves through a fluid. Fluid molecules most near the object will be pulled along with it’s surface. The sudden loss in molecules creates a low pressure(vacuum)area just above the surface or ‘Tripping the fluid’. A vortex is cause by the rolling action taken by the fluid after tripping over the surface of the object.

Watch on stem-stims.tumblr.com

Kalliroscope 2

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Flare animo.

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F1 is more than just racing, it is an engineering battle. In this gif you can see the absolute control of wing tip vortices generated from the front wing. This is just an example to show the extreme aerodynamics that these vehicles are engineered for.

Have a great day!