Soccer balls such as the Adidas Roteiro that have been used in soccer tournaments thus far had 32 pentagonal and hexagonal panels. Recently, the Adidas Teamgeist II and Adidas Jabulani, respectively having 14 and 8 panels, have been used at tournaments; the aerodynamic characteristics of these balls have not yet been verified. Now, the Adidas Tango 12, having 32 panels, has been developed for use at tournaments; therefore, it is necessary to understand its aerodynamic characteristics. Through a wind tunnel test and ball trajectory simulations, this study shows that the aerodynamic resistance of the new 32-panel soccer ball is larger in the high-speed region and lower in the middle-speed region than that of the previous 14- and 8-panel balls. The critical Reynolds number of the Roteiro, Teamgeist II, Jabulani, and Tango 12 was ~2.2 × 105 (drag coefficient, C d ≈ 0.12), ~2.8 × 105 (C d ≈ 0.13), ~3.3 × 105 (C d ≈ 0.13), and ~2.4 × 105 (C d ≈ 0.15), respectively. The flight trajectory simulation suggested that the Tango 12, one of the newest soccer balls, has less air resistance in the medium-speed region than the Jabulani and can thus easily acquire large initial velocity in this region. It is considered that the critical Reynolds number of a soccer ball, as considered within the scope of this experiment, depends on the extended total distance of the panel bonds rather than the small designs on the panel surfaces.

The purpose of this study was to compare the basic aerodynamic characteristics of a previously developed 8-panel soccer ball with those of a new 32-panel soccer ball by conducting wind tunnel tests. Experimental results show that the critical Reynolds number (Re) was approximately 3.3 × 10⁵ for the 8-panel ball and approximately 2.4 × 10⁵ for the new ball, i.e., the Re of the new ball was slightly lower than that of the 8-panel ball. We conclude that the aerodynamic drag coefficient of the new 32-panel ball is closer to that of a golf ball than an 8-panel ball.

The configuration of new soccer balls has closely approached a perfect round shape by not only reducing the number of panels but also by eliminating roughness of the panel joints by utilizing thermal bonding process recently. Therefore, in a non-rotating or low-rotating moving shot, a soccer ball drops and curves, i.e. motion by the change of wake flow, which is called a knuckle ball effect. Factors of the knuckle ball effect on the new soccer balls were investigated in case of a non-rotating shot and a low-rotating one. A correlation between fluctuation of the wake and fluid forces was identified in a symmetric panel configuration of the ball. The asymmetric configuration of the ball panel was also investigated as a factor to bring unpredictable change of the ball flight path. The low-rotating ball changes its frontal area against the moving direction and it produces irregular lateral forces. Consequently, the factors which produced the knuckle ball effect were found to be different from the case of non-rotating shots and low rotating shots.