In Detail: Aerodynamic Testing In GM's Wind Tunnel

This week's episode of TRANSLOGIC features Suzy Cody, a GM Aerodynamic Development Engineer who also happens to have blue hair and participate in a Roller Derby league. When not lacing 'em up as "Shovey Camaro," Cody is working diligently on improving the fuel economy of vehicles in the wind tunnel at the GM Tech Center. Basically, aerodynamic efficiency boils down to one metric: drag coefficient (Cd). This is the measurement of how drag force impacts a vehicle's ability to efficiently travel through wind resistance. The smaller the Cd value, the more aerodynamic the vehicle and, put simply, the less often you have to make a stop at the gas pump.

Cody has focused much of her efforts on the redesigned 2013 Chevy Malibu midsize car. After 4 years and more than 400 hours of wind tunnel tuning, Cody and team have managed to achieve a drag coefficient near that of the Chevy Volt's .28 Cd according to GM. That means up to a 2.5 highway MPG improvement over initial, unrefined exterior designs.

How did they do it? The Malibu's rearview mirrors were designed to deflect wind away from the car, the headlights and front fascia were adjusted to direct airflow smoothly along the side of the vehicle, and shutters were installed in the lower grill that close when additional engine cooling isn't required. That may not sound like much, but each minor adjustment involves hours of clay modeling, rapid prototyping, testing, and ultimately lead to changes in the vehicle's exterior design.

In order for all that testing to produce to accurate and repeatable results, you need a controlled environment. That's where the wind tunnel comes in. A giant fan with a diameter of 43' spins at 270 RPMs, or about 400 MPH, to generate wind speeds of up to 125 MPH. Engineers then use a number of instruments to measure the effects of the airflow on the vehicle, the most visually compelling of which is called the "smoke wand." This is the long stick that releases a slim stream of smoke into the wind tunnel chamber which allows the engineers to visualize airflow over the vehicle in real time.

Click the image below to watch TRANSLOGIC 67: Wind Tunnel:

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