The Skjærup blueprint

In this blogpost we try and explore a fundamental phenomena called the Kelvin-Helmholtz instability and exemplify it with a paperweight toy.

• What is the Kelvin-Helmholtz instability
• What is the role of viscosity
• Toy world example
• Conclusion

What is the Kelvin-Helmholtz instability

First of all, lets try and understand what is the Kelvin-Helmholtz instability. The Kelvin-Helmholtz instability is not a person with a mental health issue, rather it is the naturally occurring instabilities which develop when two fluids of opposite nature try and pass each other.

These instabilities play an important role in everything from the development of clouds, hurricanes, tornadoes and wind gusts down to mixing of saline sea-water, temperatures and development of waves.

What is the role of viscosity

Swirls and vortices are needing to be dissipated by internal frictional forces on scales not visible for the human eye. This is where the viscos part of the equations come into play.

Viscosity is the internal resistance of fluids mixing arising from natural phenomena such as Kelvin-Helmholtz instabilities. The more viscos fluids resist mixing and visa versa.

Toy world example

The Kelvin-Helmholtz instability is explained through large-scale phenomena above, such as the creation of clouds. However, the phenomena appears on all scales including more tangible scales such as paperweights.

By injecting a dense fluid with dye and filling up the container with water, it is possible to create the illusion of a drifting ship within the ocean. See Gallery 1.

By tilting the resulting mixture of colored (dense fluid) and lighter (water) it is possible to create a turbulent seas which then creates waves inside the container.

This creation of waves is also caused by the Kelvin-Helmholtz instability within the fluid interfaces. The viscosity and top floating pressure of fluid helps to stabilize the system after a short while. The result is an interactive toy boat paperweight bouncing around in disturbed seas.

Conclusion

In this blogpost we have explored the naturally occurring phenomena that is the Kelvin-Helmholtz instability. Furthermore we have exemplified it with a toy paperweight.