Amateur Aerodynamics

In the first installment of this series, I wrote about the fallacy of using a “template” to guide aerodynamic modifications . This second part brings us to a related topic: testing. Testing is an Absolute Necessity, Not an Unnecessary Frivolity   The claim: Since we know what the “ideal” shape looks like and can predict airflow over a car, all we have to do is build something to that shape and it will be guaranteed to work. There’s no need to test anything.   Eliminating guesswork by...more guessing. Sounds legit. The reality: Because of the complexity of the flow around a car, “automobile aerodynamics is still dominated by empiricism,” as Hucho wrote in Aerodynamics of Road Vehicles . Simulations have replaced some of the development previously done in wind tunnels as computers have become more powerful and faster, but there is still no way (and likely never will be) to design a low-drag car by following simple principles of shaping such as the “template” discussed previou...

My attitude hadn’t changed when, a few years later, I purchased the car I really wanted: a 2013 Prius. Here was a vehicle that had undergone significant aerodynamic development; Toyota advertised at the time that the third-generation Prius had spent more hours in a wind tunnel than any of the manufacturer’s other cars up to that point. Imagine my surprise, then, when I found that the forum members on Ecomodder thought there were significant problems with the car. I don't even have a picture of it stock; I got right to work modifying it according to "conventional wisdom." Specifically, their issue was with the taper of the roofline profile. Members were fond of using the Template as a litmus test for assessing the aerodynamic performance of cars based solely on comparing pictures. The user behind the Template went so far as to brand this “dimensional analysis,” giving it an incredible air of authority with the site’s other members. Someone had superimposed the Template ove...