The Science of Speed:
How CFD Revolutionized Automotive Aerodynamics
When we think of the sleek curves and impressive speeds of modern sports cars, we might assume they are solely the product of cutting-edge engineering techniques and advanced materials. However, the truth is that the science of automotive aerodynamics has been evolving for well over a century. Today, one of the most important contributors to this field is computational fluid dynamics (CFD), which has helped designers and engineers to create vehicles that are faster, more efficient, and better able to meet the needs of their drivers and passengers.
A Century of Speed: The Evolution of Automotive Aerodynamics
Early Pioneers and the First Wind Tunnel
The history of automotive aerodynamics dates back to the earliest days of the automobile. While early cars were often boxy, the race for speed and efficiency soon pushed designers to consider the impact of wind resistance. The key to unlocking this science was the wind tunnel.
Though first developed for aeronautics in the 1870s and famously used by the Wright Brothers, wind tunnels were soon adopted by visionary automotive engineers. In the United States, Chrysler Corporation began pioneering work in the late 1920s, building a dedicated wind tunnel and collaborating with aviation expert Orville Wright. This research led directly to the 1934 Chrysler Airflow, a mass-produced car that brought aerodynamic principles to the American public.
Simultaneously in Europe, Hungarian engineer Paul Jaray, who had designed Zeppelin airships, became fascinated with creating an ultra-aerodynamic car. Working at the German aircraft company Luftschiffbau Zeppelin, Jaray used his wind tunnel expertise to develop a revolutionary teardrop-shaped car body, which he patented in 1922.
Paul Jaray with a scale model of a Zeppelin Airship in a wind tunnel
The Streamlined Showdown: Chrysler vs. Tatra
Jaray’s groundbreaking design was licensed by the Czech company Tatra and brought to life as the Tatra T77 in 1934. That same year, the Chrysler Airflow debuted at the New York Auto Show. The two cars represented two different paths to the same aerodynamic goal:
The Chrysler Airflow was a mass-market innovator. Built with a rigid steel frame, it was affordable and produced in large numbers, with over 50,000 sold during its run. It was a bold attempt to make aerodynamic efficiency accessible.
The Tatra T77 was a hand-built, exclusive marvel. With fewer than 250 of the T77 and its successor, the T77A, ever made, it was a showcase of radical design.
The later Tatra T77A (1935) was particularly remarkable. Its 75-horsepower, air-cooled V8 engine could propel the car to a top speed of 150 km/h (93 mph). This incredible performance from a modest engine was possible only because of its revolutionary ability to limit aerodynamic drag
Understanding Drag and the Coefficient of Drag (Cd)
What makes a car "aerodynamic"? It comes down to minimizing drag.
Drag is a resistive force that acts in the opposite direction to an object's motion as it moves through a fluid (like air). It is caused by friction and pressure differences.
The Coefficient of Drag (Cd) is a dimensionless number used to quantify this resistance. A lower Cd means the object is more aerodynamic.
The formula to calculate the drag force (Fd) involves the drag coefficient:
Fd=Cd⋅21ρv2A
Where ρ is the fluid density, v is the speed, and A is the frontal area of the object.
The Tatra T77A is a legendary example. Its reported Cd was a stunning 0.212—a figure that would still be competitive with today’s most advanced electric vehicles like the Tesla Model S and Lucid Air.
(T77 - Courtesy wheelsage.org)
What is a coefficient of drag?
While wind tunnels were the only tool for decades, the latter part of the 20th century saw the rise of a new technology that would change everything: Computational Fluid Dynamics (CFD).
From Wind Tunnels to Virtual Testing
CFD is a type of computer simulation that models how fluids like air flow around objects. Initially used in the 1980s as a support tool for physical wind tunnel testing, CFD's role grew exponentially with increases in computing power.
By the 1990s and 2000s, CFD was being used to design complex components like side mirrors, underbody panels, and engine cooling systems. Today, it has advanced to the point where some vehicles are designed almost entirely in a virtual environment, saving immense time and cost. The technology is now so precise it can even be used for aeroacoustics simulations to minimize on-road wind noise.
(courtesy Richard Owen – Supercars.net)
Case Studies in Digital Design
The McLaren P1, a high-performance supercar, was designed using CFD to optimize its active air ducts and innovative use of titanium and carbon fiber, allowing it to reach speeds of 217 mph.
The Tesla Model S was designed with heavy reliance on CFD software. This resulted in a drag coefficient of just 0.24, making it one of the most aerodynamic production cars in the world and contributing to its impressive electric range.
(CFD Generated Image Showing Predicted Flow Patterns Around a Tractor Trailer)
Modern Aerodynamic Innovations
Today’s automobiles are the result of decades of aerodynamic refinement. Modern innovations focus on both passive and active systems to manage airflow with incredible precision.
The Rise of Active Aerodynamics
Active aerodynamic systems use sensors and actuators to dynamically adjust the vehicle's shape in response to driving conditions.
The Porsche 911 GT3 RS features an adjustable rear wing that alters its angle to either reduce drag for straight-line speed or increase downforce for high-speed cornering.
The Lamborghini Huracán Performante uses an active system that adjusts front and rear spoilers in real-time to optimize airflow for faster lap times.
(Wind Tunnel Testing of Navistar's "Catalist" Concept Truck, Including Skirts, at NASA’s Ames Research Center – Photo Courtesy of Navistar)
Airflow Management for Efficiency and Cooling
Beyond active systems, modern cars employ an elaborate set of design features to manage airflow. Strategically placed vents, grilles, and hood scoops channel air to reduce drag, cool the engine and brakes, and enhance stability. Even the underbody is critical, with flat panels and diffusers designed to smooth airflow.
Perhaps the most common example on our highways are the large skirts seen on tractor-trailers. These simple panels significantly reduce drag and improve fuel efficiency for long-haul trucking.
(Porsche 911 GT3 RS Adjustable Rear Wing in Wind Tunnel Testing - courtesy Porsche)
Airflow Management for Efficiency and Cooling
Beyond active systems, modern cars employ an elaborate set of design features to manage airflow. Strategically placed vents, grilles, and hood scoops channel air to reduce drag, cool the engine and brakes, and enhance stability. Even the underbody is critical, with flat panels and diffusers designed to smooth airflow.
Perhaps the most common example on our highways are the large skirts seen on tractor-trailers. These simple panels significantly reduce drag and improve fuel efficiency for long-haul trucking.
The Competitive Advantages of Adopting CFD
For automakers, incorporating CFD into the design process provides a clear competitive edge.
Improved Fuel Efficiency
By simulating airflow and identifying areas that create unnecessary drag—such as wheel wells and side mirrors—engineers can make targeted changes to streamline a vehicle. This directly translates to improved fuel efficiency (or extended range for EVs), saving consumers money and reducing environmental impact.
Enhanced Vehicle Performance
CFD allows engineers to optimize a vehicle's suspension, brakes, and steering for better handling, stability, and control. For high-performance vehicles, these simulations can mean the difference between winning and losing a race. Engineers can also identify and mitigate potential issues like overheating in the engine bay or brakes.
Reduced Environmental Impact
CFD helps create more sustainable vehicles. Simulations can optimize a vehicle’s engine combustion and exhaust system, like the selective catalytic reduction (SCR) systems in modern diesel engines, to reduce harmful emissions. CFD also helps engineers design quieter cars by identifying and minimizing noise from the exhaust and air intakes.
CFD simulation showing urea injected into the SCR system of an automotive diesel exhaust.
Conclusion
The history of automotive aerodynamics is a long and fascinating one, chronicling the major milestones and innovations that have brought us to where we are today. From the pioneering physical tests of Chrysler and Tatra to the virtual design labs of the 21st century, the goal has remained the same: to move through the air with the least resistance possible. With the help of CFD, designers and engineers continue to build cars that are faster, more efficient, and better adapted to the demands of the modern world.