Aerodynamics Testing Help Chevrolet Improve Fuel Efficiency, Interior Quietness

BANGKOK, THAILAND - Whether driving along the Gulf of Thailand or on the road to Doi Inthanon, the highest mountain in Thailand, drivers are certain to encounter a lot of wind – sometimes strong enough to shake a car and noisy enough to require turning up the radio.

When automakers design vehicles they pay close attention to aerodynamics because even the smallest design elements, such as a crease in a body panel, can disrupt airflow and have a big impact on fuel efficiency and interior quietness.

To study the way air passes over, under and around Chevrolet vehicles, General Motors engineers use a state-of-the-art Aerodynamics Lab. The facility features a 228.6 meter-long long tunnel through which a 13-meter fan powered by a DC electric motor with the equivalent of 4,500 horsepower (about 3,357 kW) that can generate winds of up to 222 km/h – that’s more than an F2 tornado.

Why do the engineers need to go to the extremes?

"The wind tunnel enables us to do something that is virtually impossible on the road – to drive at highway speeds and measure the vehicle's aerodynamic performance with extreme accuracy. In the wind tunnel, we can make numerous runs under identical conditions and evaluate the smallest changes," said Frank Meinert, Technical Integration Engineer, GM Global Aerodynamics.

"The data generated by the wind tunnel is a valuable tool that can provide a measurable benefit to our customers," Meinert added.

Measured in “drag coefficient,” aerodynamics is easily affected by problem areas, such as wing mirrors, front corners, front grille design, wheel arches, windscreen rake (front and rear), rear-end design (rear fender, boot-lid, bumper design) and any other appendages that appear to be blocking an otherwise smooth airflow. These are the design elements engineers analyze in the wind tunnel, which leads to design refinements.

A vehicle with optimized aerodynamics may give customers up to 1.06 kilometers per liter in additional fuel economy – one of the top purchase considerations for customers in Thailand. With a standard 55-liter fuel tank, customers get an added 58 kilometers per tank. Enhanced fuel economy also means less CO2 emissions. The engine does not need to work so hard to keep a vehicle cruising at a given speed, burning less fuel and producing less CO2.

Aerodynamic design also results in a quieter interior – a top 10 purchase consideration for premium car shoppers and an attribute known to impact to customer satisfaction across all segments. By achieving interior quietness through aerodynamic refinement, automakers can rely less on heavy sound-insulating materials, the elimination of which can help improve fuel economy as well.

To a certain extent, good aerodynamics also promotes safety. Aerodynamic stability at highway speeds help keep the vehicle planted to the road, enhancing the mechanical grip offered by the tires. Additionally, it is less likely to suffer from wind-buffeting, which could upset the vehicle’s balance under extreme circumstances.

Aerodynamics does not apply only to sedans such as Cruze, pickup trucks like Colorado and SUVs like Trailblazer are also affected. Some aftermarket accessories have varying impact on aerodynamics. For example, add-ons like bug deflectors on the bonnet, wider or mud tires and aftermarket off-road bumpers can raise the drag coefficient, in addition to weight. The result: added noise and increased fuel consumption.

According to a GM aerodynamic performance engineer, a long-disputed topic among truck owners is whether a tailgate raised or lowered is better for aerodynamics. The fact is, a tailgate in the up position is more aerodynamically efficient. As air flows over the truck, it falls over the cab and pushes forward on the rear of the truck. With the tailgate down, the benefits of that airflow are diminished.

So what accessories can truck owners add to help aerodynamics? Tonneau covers for the bed help smooth airflow over the truck, and Bloch says soft covers are more beneficial than hard covers because they form to how the air wants to flow. Running boards (some call it side-steps) can also help air flow smoothly down the truck’s sides. Round, tube-style running boards can provide a minor improvement to as truck’s drag coefficient, although fully integrated, factory flush-mount running boards are better.