In the name of aerodynamics: GM engineers look at how the wind blows at test facility
Carmaker adds reduced-scale wind tunnel to match vehicle models
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When it comes to saving fuel, a car’s engine is only part of the puzzle. Aerodynamic styling plays a huge role, and so engineers use wind tunnels to assess models as they’re being developed.
It’s common to use full-size vehicle models, made of malleable clay for quick design tweaks, but some automakers also use scaled-down versions. General Motors recently added a wind tunnel that’s equally scaled down to match these vehicle models, sized at 40 per cent of a full-size wind test facility.
The company previously tested these smaller clay models alongside regular ones in its full-size wind tunnel, but needed extra capacity. Building a smaller tunnel specifically for these models increased overall testing capability, but at far less cost than adding a second full-size tunnel.
“It took about 18 months to build and we’re doing readiness testing,” says Jeff Bordner, engineering group manager for the GM aerodynamics lab in Warren, Mich. “Production testing should begin in January.”
How it’s done
The vehicles start with either wood or metal frames. These are covered with foam and topped with a layer of clay. During testing, clay can be added or shaved off to tweak the vehicle’s design, and it’s much quicker and easier to do this on a smaller-sized vehicle. Adding half a kilogram of clay to a 40 per cent model is the equivalent of slathering more than seven kilograms onto a full-size one.
The model faces the wind blowing out of the tunnel as its wheels turn on moving belts in the floor, simulating driving on a road. Cameras and sensors record the test, feeding information to banks of computers in an adjacent laboratory. Engineers use a device that creates smoke in front of or alongside the car, so they can see how the wind moves over the model’s shape and where it meets resistance or creates turbulence.
It’s similar to when you hold your hand out the window of a moving car: You feel resistance when your hand is straight up, versus holding it flat with your fingers forward. Even a minor change to a mirror or fascia can make a considerable difference in how the air flows around the design.
“We’re measuring the force the wind is putting on the vehicle,” Bordner says. “You want to reduce the drag force to make it more aerodynamic, so we get the best shape for the vehicle we’re trying to develop.”
• Aerodynamic improvements are the most cost-effective method for improving fuel efficiency, versus powertrain technologies or pricey lightweight materials.
• The clay models have moving suspensions, simulated engines and cooling systems, full underbodies, and open grilles, since these all affect wind resistance.
• The scaled-down models weigh about 200 kilograms and are moved with a small crane.