General Motors has an awesome new $30 million gadget at its Warren, Michigan Technical Center: a reduced-scale wind tunnel with advanced instrumentation and a rolling ground plane. Here’s a detailed look inside.  

At the General Motors Technical Center in Warren, Michigan, the automaker operates one of the finest full-scale wind tunnels in the country, a massive 4500-horsepower facility constructed in 1980. (See MCG’s look inside here.) And now, right next door, GM has just completed an advanced $30 million reduced-scale wind tunnel, which is specifically designed to handle smaller 33 percent and 40 percent scale models.

Why a reduced scale wind tunnel when GM already has a perfectly suitable full-scale tunnel? In a word, efficiency. The reduced scale tunnel can produce aerodynamic improvements faster and cheaper. Just one example among many: Moving one pound of styling clay on a 40 percent model is equivalent, in time and effort, to moving 16 pounds on a full-scale model. Thus more iterations can be tested in less time, speeding and improving the development process.

Coupled with GM’s other aerodynamic tools, including the full scale tunnel and CFD (computational fluid dynamics; a virtual wind tunnel if you will—see the MCG feature), the reduced scale tunnel will help the General to make its cars more aerodynamically efficient. And that’s a big deal. GM has determined that aero is by far the most cost-effective means of reducing both carbon dioxide emissions and fuel consumption, which is a win-win deal for the environment and for car buyers. (The relationship between CO2 and fuel consumption is essentially 1:1.) Here’s a quick tour of the reduced scale tunnel.

SAE editor Lindsay Brooke was included in this photo to show the size of a 40-percent scale Chevy pickup. (Is this model cool or what?) For aerodynamic realism in the tunnel, the entire suspension and undercarriage are precisely duplicated on each model, a feat that can now be accomplished quickly and economically using rapid prototyping and 3D printing technology. All the model work is performed in-house by UAW technicians.

This mirror shot shows the chassis detail on a 40-percent model. Note how the driveline, exhaust system, and fuel tank have been precisely duplicated in plastic and aluminum billet. In the pursuit of drag reduction, the airflow inside and under the body can be just as critical as the airflow over the body. The reduced-scale models weigh around 450 lbs. each—much faster and easier to move in and out of the tunnel than full-sized mockups.

Here’s a 1/3 model sedan resting in the test section. The long gray belt passing between the wheels is a rolling ground plane (aka rolling road), which replicates the airflow of a car travelling over pavement. Four more smaller planes spin each wheel at a designated road speed. Under the floor, which can rotate 360 degrees, is a six-element electronic balance system that precisely measures all the forces on the model as the air travels over it, including lift, drag, and downforce.

Nina Tortosa, senior aerodynamicist and wind tunnel operations engineer, uses a smoke wand to visualize airflow over a 1/3 scale model in the test section. While low-speed air is used for smoke testing, the tunnel normally blows at up to 250 km/h, or 155 mph. (Increased airspeed proportionally adjusts for the scale model’s reduced dimensions.) An 1100 hp electric motor and 11.5-ft, 18-blade propeller move the air mass, while a water/air heat exchanger maintains the air temperature at a constant 72 degrees.

A control console adjacent to the tunnel allows complete remote operation, including data gathering and safety functions. A set of light beams will trigger and shut down the tunnel if a human unexpectedly enters the test section.

Now that the reduced scale tunnel is up and running, the full scale facility next door will be upgraded over the next year with its own full scale rolling ground plane and other enhancements. The wind tunnel improvements are part of a $1 billion plan to expand and renovate the entire Technical Center in Warren, which opened in 1956 and was recently designated a National Historic Landmark.