Simulation results superimposed on a catch.

As official supplier to the NFL, Wilson Sporting Goods takes their footballs very seriously.  They recently simulated the aerodynamics of their venerable NFL football designs with some help from consultants from CD-adapco who used their STAR-CCM+ simulation software. 

According to CD-adapco, CFD analysis of ball flight was previously limited to fundamental models where simplifications in ball shape and flow physics affected the accuracy of the results. To get truer data, designers would have had to revert to costly wind tunnel tests.

Now cloud-based processing can allow for a more realistic simulation, including the panels, seams, valve and stiches of the ball in the CFD analysis. This additional realism more accurately reflects the turbulent and laminar flows around the ball, which in turn affect the overall aerodynamic drag and stability.

In an interview with ENGINEERING.com, David Vaughn, Vice President at CD-adapco said, “It was interesting to see how the laces and inflation valve affect the airflow around the ball during flight. With our simulations, we are even able to spiral the ball. But we simulated a perfect spiral: what about non-perfect spirals and the end-over-end rotation of a kick? Conducting a complete analysis would have to consider all of those factors.”

When asked about how he would improve the flight of the ball, Vaughn declined based on client confidentiality, suggesting instead that we, “look at other ball improvements like golf balls and soccer balls. Adidas made huge changes to the panels on World Cup soccer balls over the past 12 years.  In golf you see different dimple patterns to achieve different performance.  As for a football, you can see the effect of the spiral shaped toy balls that help kids throw a tight spiral.”

Dimples make golf balls fly farther by affecting the lift and drag the ball experiences during flight.  The drag impedes the forward motion, while the lift acts perpendicular to that motion.  As the golf ball flies, it creates a high pressure area in front of its motion that forces air to flow around it in a laminar flow (orderly airflow). This air flow will separate, however, around the back of the ball, creating a wake of turbulence and low pressure behind the ball that increases the total drag. The dimples on the ball create a layer of turbulent flow around the ball that reduces the turbulence in the wake.

Vaughn clarified “Anything to keep a turbulent boundary layer on the surface of the ball will improve the flight. People think that laminar flow, around the ball would be best as it reduces viscous drag. However, this is not stable due to the flow separation point on the downstream end of the ball. The goal then is to keep the air flow attached to the surface of the ball as far back as possible. This happens when the viscous boundary layer on the ball is tripped to a high energy turbulent boundary layer.”

He added that, “this makes the football laces and air valve necessary protuberances that help to energize the boundary layer. The texture will help as well but not as much as say the golf ball dimples.”

At the time of the study, Wilson’ VP of R&D, Doug Genther said that, “the ability of STAR-CCM+ to accurately and efficiently solve unsteady flows with boundary layer transition was certainly a key technical factor, but equally important is the support and flexibility offered by CD-adapco. Their dedicated support model and Power-on-Demand offering is an ideal solution for our needs.”

In the sports world, technical innovations like using simulation to optimize the design of sporting equipment, can be very controversial. “Technological doping” has affected many sporting industries from Olympic swimming/skating, auto racing, and even sailing. 


Football signed by President Gerald Ford when playing for University of Michigan.

In football, the fundamental design has been unchanged for almost a century.  Even if analysts could design a “better” football, would they?  “If you would talk about designing a new football, you would meet extreme opposition,” said Vaughn.   

Watch the video below to see how the tradition of football manufacturing lives on at Wilson’s football production facility.

With respect to this year’s game Vaughn adds, “it would be interesting to simulate how the cold weather, snow, and rain would affect the ball’s flight.” Perhaps one day we will find out.

Source and Images courtesy of CD-adapco.

Reference Scientific American

 

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