CFD stands for Computational Fluid Dynamics and is the source of all those beautifully-rendered, streamlined pictures generated and displayed whenever someone talks about aerodynamics. But what does it actually take to generate those pictures, and is that really the whole story?

The equations governing fluid flow are some of the most complicated and difficult to solve in any engineering discipline. The only way to actually write out an analytical solution by hand is to simplify the problem heavily (inviscid, irrotational, 2D planar, Newtonian etc.). The problem here is that these solutions only work as rough approximations to real life in very limited circumstances. The aerodynamic profile of a car, for instance, is not an easily-defined shape for which you can derive a solution on two sides of A4.

The above equation is a vector notation version of the Navier-Stokes equation governing fluid momentum and is highly nonlinear if all terms are considered.

To get around this we make approximations in a different way. Rather than treating the whole volume as containing the fluid in question, you break it down into tiny cells and consider each one individually.

If you consider a tiny cell such as a triangle, tetrahedron or…
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