Volume II, Issue 3, Page 36
Wind Tunnel In A Can
CFD Shaped Impala SS Body
By Glen Grissom
images Courtesy GM Racing
CFD-generated illustration compares the aerodynamic characteristics of the NASCAR Impala SS (right) and the Monte Carlo SS (left). The colors of the streamlines around the cars show the pressure in the surrounding air from Red (high pressure) to Blue (low pressure). Aerodynamic downforce is shown here by the dark red on the streamlines passing over the Impala SS’s front splitter.

I first saw Computational Fluid Dynamics (CFD) in use for racing in New Mexico at then Indy car powerhouse team Galles Racing in the late ‘80s. They had a state-of-the-art Silicon Graphics (SG) computer workstation running a custom-written CFD program to help design and model their front and rear wings for their Indy cars.

Although I had worked in an R&D section of the old-line Burroughs computer company years before, this real-time aero-evaluation of a racing wing model on-screen was about the coolest use of a computer I had ever seen up to that point. Talk about being blinded by the light – and the big bucks. The SG workstation was at least $30,000 and the CFD programming that much or more.

I wasn’t a computer noob -- I was fortunate to have seen a demo around 1980 on a desktop-sized computer running the Smalltalk computing language with a computer mouse and graphical user interface (GUI) -- when some visiting computer scientists from the Xerox Palo Alto Research Center (PARC) showed us at Burroughs the future years before it came true. PARC – the people who invented the laser printer; Ethernet; LANs; email; GUI; desktop publishing; essentially the first portable workstation computer; Smalltalk (which eventually begat Windows)  – really, really, really smart, world-class computing people – most of whom left to build companies like Apple, Adobe, and others.

A conventional rear spoiler on a Monte Carlo SS race car (top) produces high pressure on the rear fenders, indicated by Red. The plates mounted on the ends of the rear wing on the Impala SS race car (bottom) can be adjusted to produce low pressure on the left side of the vehicle (see Blue on wing plate), increasing side force and enhancing stability in high-speed corners, similar to the feathers on an arrow.

But aero-modeling of prototype race car parts without a wind tunnel? That was equally amazing. Only a few years before, it would have taken a defense contractor budget and a room the size of a 4-car garage filled with the latest mainframe computer gear to do this – or a hanger stuffed with engineers with greased slide rules. But here was a minicomputer with 3-D graphics and computations to simulate the aero forces on those race body parts. I had seen the beginnings of what I then called “a mini wind tunnel in a can.”

Now, 25 years later the processing and computational power of that very expensive SG computer workstation is available in a desktop; albeit not your father’s desktop, but a modern maximum processor hot-rodded one. And the CFD programming isn’t limited to modeling certain smaller parts of a race car body, but can aero-model the entire assembled body. All this in now possible before you ever have to fire up a multi-million dollar real-word wind tunnel, which is usually reserved for production cars nearly 24-7-365 -- let alone pay for the travel to/from, etc. for your race team.

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