A Journey in the Mechanics and Aerodynamics of Porous Footballs

Abstract

In early 2024 the sporting goods manufacturer Wilson released their 3D printed Airless Basketball. The most notable design feature of this ball was its unique lattice structure leading to a large amount of porosity. Wilson’s advertising campaign placed heavy emphasis on their iteration for identical mechanical properties to a regulation basketball but chose not to discuss how this geometry would effect the ball’s aerodynamic properties. This project serves as an extension of this work to the world of football, with an emphasis on answering the question of how porosity changes the movement of a ball through the air. The aerodynamics of spheres as well as sports balls is a very well researched area with the ’drag crisis’ phenomenon featuring heavily. This is when the Coefficient of Drag of a sphere will dramatically decrease at higher speeds. Through wind tunnel measurements of balls with differing porosity, this project concluded that for low porosities we see similar drag crisis behaviour. This is coupled with an increase in drag for all porosities compared to the solid case, even up to the limit of 95% open surface area which staggeringly sees on average 1.5 times more drag than the solid case for all velocities tested. Particle Image Velocimetry was then carried out to gain understanding of the the flow field around these balls. This project then moves into mechanical design and analysis of 4 full size models to explore the tradeoff between mass and deformation that is inherit in this design process. We conclude that while it is unlikely that this product would be viable in the professional game, the ability to manipulate its geometry may prove fruitful in making a novel and exciting product for the amateur player.