Why the dimples smile on golfers

The average weekend duffer knows the dimples on a golf ball help it to fly farther. But not even Tiger Woods can say how they work; manufacturers have relied largely on trial and error in their quest for the ultimate orb.

Enter a team of engineers from the University of Maryland and Arizona State University.

Using a supercomputer, they solved the equations that govern aerodynamic flow at more than a billion points on a golf ball's surface.

They shared the results yesterday at the annual meeting of the American Physical Society's Division of Fluid Dynamics.

It was known that dimples reduce drag on a ball by about one half, by keeping the airflow from separating from the ball's surface as long as possible.

After running 500 parallel processors for 300 hours, the team can now describe why that is true mathematically. It's not the sort of thing that can be put precisely into words, but Arizona State engineering professor Kyle Squires took a stab at it.

"The dimples have the effect of energizing the airflow very close to the surface," Squires says.

In the picture, the colors reflect different rates of rotation of airflow. Red and blue represent opposite flow directions; yellow is neutral.

Now that the engineers have solved the equations for one virtual ball, they are starting to get an idea which dimple designs will work better. The research was sponsored by the maker of Srixon golf balls, so some of the results are proprietary.

The research may also offer clues as to how dimples could be used in other technologies, such as turbine blades, Squires says.

But will it improve his handicap? Not likely, if only because his kids keep him from getting much time on the links.

- Tom Avril