According to General Motors, aerodynamic drag accounts for 20% of the energy consumed in an average vehicle, making a direct impact on vehicle fuel efficiency. GM designers are increasingly looking to aerodynamics as a way to improve fuel economy across the brand’s range of vehicles, most notably for the next-generation Chevrolet Volt electric vehicle.
For the Volt, aerodynamic improvement represents a critical step in meeting the range targets necessary for moving the vehicle to a final production design. The vehicle’s design team has been working closely with engineers, aerodynamicists, and other scientists to optimize the car’s aerodynamics.
“One of the ways design can contribute to the efficiency of any vehicle is through the aerodynamics and the body shape,” said Ed Welburn, Vice President of GM Global Design. “The collaboration between a designer and an aerodynamicist can not only contribute to improved fuel economy or extended range, but can produce beautiful and different body shapes.”
“The electric range of the Chevrolet Volt is most sensitive to improvements in aero, which is in contrast to a traditional vehicle program in which mass typically plays a larger role,” said Frank Weber, Global Vehicle Line Executive and Global Vehicle Chief Engineer for the E-Flex System.
In addition to fuel economy, a vehicle’s range, emissions, and acceleration are all affected by wind resistance, or aerodynamic drag. The cooling of components such as radiators and brakes is affected by airflow, as is cornering capability, crosswind response, directional stability, and on-center handling. GM’s aerodynamics laboratory, located at its technical center in Warren, MI, allows for testing and development of each of these characteristics.
Aerodynamics development begins with a 1/3-scale model, which features a highly detailed underbody and engine compartment, where basic shape and major features are defined. Radiator and underhood cooling flow is developed using CFD models, and computation development is conducted to determine aerodynamic drag of design alternatives. Full-scale models are then used for shape refinement and optimization of wind noise. The development process concludes with a vehicle prototype validation of the math-based analysis and physical testing.
“I’m proud to say that after extensive aero development of the Volt, and more to come, we have achieved a vehicle that had a coefficient of drag that is more than 30% lower than the original concept,” said Welburn. “It’s not easy, but it is a necessity.”
GM’s aerodynamics laboratory was built in the late 1970s in response to fuel shortages and the introduction of corporate average fuel economy (CAFE) standards. It was the first full-scale automotive wind tunnel built in North America and remains the largest wind tunnel in the world dedicated to automotive testing.
Test operations at the site began in 1980 with several production vehicle tests that benchmarked the wind tunnel’s performance against other facilities. Today, all new GM vehicles for the North American market are developed using the lab in addition to CFD analysis.
Wind speed in excess of 120 mph (193 km/h) can be achieved in the tunnel, and real-time data-acquisition and display systems measure forces and moments, airflow velocities, pressures, temperatures, and wind noise.