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I recently had the opportunity to tour General Motors’ brand new reduced scale wind tunnel, where future car designs are tested and refined. Come take a look inside!
Disclaimer: I am currently working on contract to General Motors, but share this as an armchair aero-geek.
What makes this wind tunnel special?
GM’s full-size wind tunnel, which tests 1:1 scale vehicles as well as scale models, began operation 35 years ago and the industry has learned a lot about aerodynamics and wind tunnel design since then.
The new $30 million tunnel features a cutting-edge five belt ‘rolling road’ design that, with four rollers under the model’s carbon fiber tires and one down the middle, better simulates the effects of driving on a real road.
It is an open layout as well. This means that the testing area is not enclosed, and testers can stand very close to the model without affecting results. Since there are no walls enclosing the test area, you can actually see the return path of the wind tunnel on the far side of the car.
How fast does the air go?
The top speed of the tunnel is 155mph. As shown at the end of the video above, though, that equals out to a lot lower speed considering the model’s scale. A 1/3 scale model will only get hit with 1/3 as many air particles, so to get results consistent with full-size testing, the air has to be going 3x the speed. So, considering the size of the models being tested here, 155mph is equivalent to about 60mph for a full size car.
That’s a pretty cool car model.
You’re damn right it is. Anywhere from 30-40% the size of a real car, each 450-lb model tested here has several special features to accommodate the rolling road setup as well as return more accurate data.
The car sits on four weight-sensitive posts which are set in the tire wakes to reduce disturbance. Each wheel is custom made from solid aluminum, and each tire from carbon fiber. With the speed that these wheels turn, this was the best way to keep vibration down.
But it doesn’t stop there. Every model not only has custom machined, fully operational suspension (with springs just big enough to keep the wheels from bouncing on the rollers), but they have accurate underbodies, engine bays and grilles as well. All of this makes each scale test a bit more accurate, which means there will be less guess-work when it comes to predicting the CdA of the full size model, and even final production vehicle.
Of course, most tests do not use foam models. During the design process, studios release math data to be milled in clay onto an aero armature like this Impala below. Different grille and other aero options are rapid prototyped and swapped to find the most efficient configuration. Aero sculptors work air dams, flow trips and other tricks of the trade in clay, then the model is sent back to the design studio for aesthetic tuning.
Design changes can be tested more quickly with the new tunnel as well. The small metal holes in the side of the K2 and Cruze models are used to lift and transport each model via a large overhead crane. To minimize down time, models being tested can be swapped within a minute. While one model is testing, sculptors can try out ideas on another.
Why should I care?
With ever-tightening fuel economy regulations from the federal government as well as tougher competition among other companies’ fuel efficient offerings, aerodynamic testing actually helps us get cooler cars on the road. Lowering aero drag through styling modifications (therefore raising fuel economy regardless of power plant) allows automakers to give you more horsepower for any given platform. From a consumer’s perspective you can expect higher performance engines, higher top speeds and better fuel economy because of this fascinating and seldom-seen corner of the auto industry.