Nasa turns to sports balls to understand aerodynamics

By understanding how fluids flow around cylinders and spheres, scientists predict how even minor alterations in these basic shapes change flow patterns


A smooth golf ball travels less than half the distance of a dimpled one as the ball’s surface roughness and its distribution determines its aerodynamics. Photo: AFP
A smooth golf ball travels less than half the distance of a dimpled one as the ball’s surface roughness and its distribution determines its aerodynamics. Photo: AFP

Los Angeles: Scientists from the National Aeronautics and Space Administration (Nasa), including one of Indian-origin, are studying the aerodynamics involved in sports balls moving through the air in order to learn how to make aircraft more Earth-friendly or help a spacecraft take the most efficient route to Mars.

Aerodynamics is the study of how fluids flow around objects. By understanding how fluids flow around basic shapes such as cylinders and spheres, scientists predict how even minor alterations in these basic shapes change flow patterns.

“Sports provide a great opportunity to introduce the next generation of researchers to our field of aerodynamics by showing them something they can relate to,” said Rabi Mehta, chief of the Experimental Aero-Physics Branch at Nasa’s Ames Research Centre in California.

The way air moves around different shapes plays a significant role in the flight of all sports balls. Researchers can demonstrate the science behind the best way to throw a football and why a ball curves using relatively simple visualisations of fluids flowing over sports balls in small test facilities.

Complementing the large and high-speed wind tunnels at Ames, small wind tunnels and water channels used for quick tests provide controlled environments where fluids at known speeds can flow over a stationary test item—in this case a sports ball.

With smoke, lasers or brightly coloured dyes inserted in the fluid flow, patterns of smoothness and disturbance appear, making the usually invisible aerodynamics around the items brilliantly visible.

“What we are looking for in the smoke patterns is at what speed the smoke patterns suddenly change,” said Mehta. “There is a thin layer of air that forms near the ball’s surface called the ‘boundary layer,’ and it is the state and behaviour of that layer that is critical to the performance of the ball,” said Mehta.

“The materials used, the ball’s surface roughness and its distribution determines its aerodynamics,” he said.

For example, a smooth golf ball travels less than half the distance of a dimpled one. The dimples make the boundary layer “turbulent” which keeps the boundary layer attached to the object longer and delays separation. When the boundary layer separates from an object, drag is created from the resulting pressure imbalance, and the object slows down.

“When a quarterback throws the football he ideally wants to throw a tight spiral with high rotation rate to help stabilise the ball as it flies through the air,” said Mehta. “This produces lower drag than a wobbling ball so it will get there faster. Wobbling balls are also harder for the receiver to catch and more easily picked off by the defence,” he said.

Kicking is another aspect of football aerodynamics. Ideally the kicker should kick the ball so that it spins along the horizontal axis, if angled the ball veers sideways. If football players can learn more about velocity, direction of motion and spin rates, they can learn how to achieve desirable results, he said.