 A conventional rear spoiler on a Monte Carlo SS race car (top) produces high pressure on the rear fenders, indicated by Red. The plates mounted on the ends of the rear wing on the Impala SS race car (bottom) can be adjusted to produce low pressure on the left side of the vehicle (see Blue on wing plate), increasing side force and enhancing stability in high-speed corners, similar to the feathers on an arrow. |
GM Racing has applied modern-era CFD for a mathematical simulation of the airflow around the Impala SS coming later this month to Bristol on March 25 and offered some insight into the process.
"The best way to describe CFD is a wind tunnel in a computer," explained Kevin Bayless, GM Racing oval track chassis/aero program manager. "CFD is a simulation that predicts the aerodynamic forces acting on a vehicle using computational methods rather than physical measurements. CFD allows engineers and racing teams to evaluate the effects of aerodynamic changes quickly on a computer screen rather than in a conventional wind tunnel."
First developed for aerospace and defense applications, CFD came to the everyday world as supercomputers (as multiple-processor-based PCs and cheap memory) became available to run the complex software programs. Those government-funded/subsidized industries were the only ones at the time that could afford the computing power and effort required to do this type of modeling, and eventually make it pay out in a product.
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The price of admission to this elevated level of prototyping technology isn’t pocket change (well, it is in comparison to 25-plus years ago), but the benefits of CFD are substantial. The sophisticated software makes it possible to "see" the invisible movement of air over a car body.
Computational Fluid Dynamics Brings Rocket Science to NASCAR
"CFD allows us to visualize the flow to understand what the air is doing and where the aerodynamic forces are being generated," said Bayless. "That's simply not possible with a model or a full-size vehicle in a wind tunnel. CFD also allows us to test aerodynamics without a physical model, which can be helpful in the early stages of a design. We can analyze and compare various alternatives before actually building a prototype vehicle." Helpful in this sense also means much less expensive. Building physical models of aero parts is a lot of art and science and not cheap.
For those who think the mandated COT body erases any brand identity for Chevy and the other manufacturers in NASCAR – me included -- Bayless notes: "Although the COT is highly regulated, it's not a spec race car. As a manufacturer, Chevrolet was able to define many of the details that separate the Impala SS from our competitors' cars. The headlights, grille, portions of the hood, and the tail were areas where GM Racing was able to incorporate Impala SS styling cues and brand identity. These areas are now fixed as part of the NASCAR Impala SS package."