## What is a fluid?

A fluid is either a gas, a liquid or a plasma. Physically it is defined as a substance that can not resist to shear forces. And that’s the point where the physical definition differs from the industrial definition, as greases are often called fluids. If your interested in lubrication, you’ll find additional information here.

## Where does one normally come in contact with fluids?

There are vast amounts of examples, but that doesn’t mean a normal person realizes it. So here is a non-exhaustive enumeration of everyday examples. Click on the examples for more information.

You breath the air around you and the lung is the pump.

Your blood flows trough your body in a closed loop. The heart is the pump and the arteries and veins are the piping.

As you drive faster the resistance induced by the surrounding air increases exponentially.

Fresh cool air is sucked towards the low pressure zone around the fire and delivers the needed oxygen for the exothermic reaction. The hot combustion air rises upwards due to the lower density.

Boiling water forms typical flows and furthermore the water evaporates from a liquid state into the gaseous state.

A complex phase-change-phenomena which you can learn more about if you jump into the meteorology-section.

## Visual example: Kármán vortex street

This is something you have seen but maybe not really realised. The picture shown below was created using a CFD simulation and shows the mean velocity around the logo. As you can learn in the CFD section, this is by no means an ideal data visualization, but looks nice nonetheless.

## Math

Fear not. If you just want an overview, you don’t need it. But as you dig deeper you may consider some simple formulas in the first place and more complex differential equations in the long run.

One of the most used formulas is Bernoulli’s equation in the stated form:

$ p_1 + \frac{\rho_1}{2} \cdot c_{1}^{2}+\rho_1 \cdot g \cdot z_1= p_2 + \frac{\rho_2}{2} \cdot c_{2}^{2}+\rho_2 \cdot g \cdot z_2 + \Delta p$

## Bibliography

The knowledge found on this website is either empirical or from a know source. All sources are gathered on a separate page and linked to from all other pages.