Can Dimples Improve Fuel Efficiency?

A company called Fastskinz thinks so. They've created a vinyl car wrap based on the aerodynamic evidence from golf balls that an uneven surface creates less drag. Popular Mechanics puts the theory to the test.
May 12, 2009, 12pm PDT | Tim Halbur
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"Since the early 20th century, golf ball makers have known that small irregularities-dimples-on the surface of balls created longer and truer drives than balls with smooth surfaces. In short, the dimples help delay the airflow separation from the ball and create a smaller wake of air behind, so there's less drag. "A golf ball is a bluff body and most of the drag is due to airflow separation-the flow cannot close behind the ball and stay attached," says Steve Ogg, vice president of golf ball research and development for Callaway. "The dimples transition the flow from a smooth laminar state to chaotic turbulent state. The turbulent mixing increases the momentum of the air at the surface of the ball, allowing it to stay attached longer." A car is obviously not the same type of shape as a golf ball, but the idea behind MPG-Plus is that dimples on a car body could have a similar effect. In automotive aerodynamics, the surface of the car is "dealing with turbulent flow," says Bill Pien, supervisor of aerodynamics in Ford Vehicle Engineering. "In normal operation, the skin friction accounts for no more then 1 percent of the total drag since the main drag generation mechanism is the vehicle shape," he says.

Fastskinz thinks there is still efficiency to be gained. They claim that the improved fuel economy of a vehicle wrapped in MPG-Plus compared with an identical vehicle not wrapped is 18 to 20 percent."

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Published on Monday, May 11, 2009 in Popular Mechanics
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