Test The Limits

Time to stop hero-worshipping the wind tunnel

By Exa

May 02 2016

The mystique of the wind tunnel as the ultimate place to perfect a car’s aerodynamics is blinding some makers to the superior abilities of digital simulation.


Retiring head of design at GM, Ed Welburn, recently got misty-eyed talking about his love of the wind tunnel in an interview with Automotive News. He called it his “second design studio” and compared the excitement working there to the designer’s equivalent of the 24 Hours of Le Mans.


It’s this conviction that persuades some makers to build ever more expensive tunnels in a misguided belief that it’s the quickest way to achieving the aerodynamic gains required by ever-more stringent emissions targets globally.


But others disagree. As this recent Car & Driver article highlights, Jaguar Land Rover has decided simulation is not only more cost-effective but achieves better results. Instead of building its own, the highly profitable British premium brand buys time in an independently-run tunnel for verification only.


There are many drawbacks to wind tunnels. Chief is not understanding why you’re getting the results shown. If you are aiming for an incredibly low drag coefficient approaching 0.20, then you need to understand the science behind it.


Simulation also allows designers to appreciate the secondary effects behind a bodywork change. For example, the change might improve airflow but it could also screw up engine or brake cooling, or create an unacceptable amount of noise in an area not covered by test sensors.


You can also experiment far more radically in simulation. Clay models can’t be modified as quickly or as dramatically as they can in a wind tunnel and that limits the range of testing you can do within a specific period of time. On a computer you can also start the process far earlier in the development period, well before the design starts becoming finalized in the minds of designers and executives. 


Finally, simulation can replicate real-world scenarios far better than a wind-tunnel. Drag figures, as with lab-tested fuel economy figures, lose all meaning if they aren’t relevant to everyday driving.