Typically, soccer balls are constructed with 32 pentagonal and hexagonal panels. More recently Teamgeist 2 and Jabulani balls have 14 and 8 panels, respectively, with dramatically different panel shapes and designs from conventional balls. The latest model called Cafusa, made with 32 panels, has been adopted by many soccer leagues. However, there are few studies on the aerodynamic characteristics of these balls. This study examined the trajectory and aerodynamic characteristics of soccer balls constructed with different numbers and shapes of panels. Results of wind tunnel tests indicated that the aerodynamic forces varied significantly according to the number of panels. The results of simulation showed that the ball trajectory changes according to panel orientation, suggesting that panel orientation has significant effects on the flight of the balls.

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Traditionally, the soccer balls used in soccer tournaments had 32 pentagonal and hexagonal panels. Also, 14- and 8-panel balls have been used. Recently, new 32-panel ball (Cafusa, Adidas) with unverified aerodynamic characteristics are using. There is a need to understand the aerodynamic characteristics of a new 32-panel ball that used a variety football league. The purpose of this study was to analyze the basic aerodynamic characteristics of the Cafusa ball (32-panel) by using a wind tunnel. Also, we measured the orientations (Face A, B, C) of the aerodynamic forces for Cafusa ball. The critical Reynolds number of the Face A, Face B, and Face C was 〜2.6 × 10^5 (drag coefficient, Cd ≈ 0.12), 〜2.4 × 10^5 (Cd ≈ 0.16), and 〜2.4 × 10^5 (Cd ≈ 0.15), respectively. The flight trajectory simulation suggested that Face C has less air resistance in the high-speed region than the other Faces. It is considered that the critical Reynolds number of a soccer ball depends on the panel orientations.

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The purpose of this study is to analyse the dynamic effects of soccer balls and the differences impact forces have on these balls. The subject under discussion is the balls that have different material surfaces and panel orientations. We chose four balls for this research: Cafusa, Jabulani, Theam Geist2 and Pelias. These soccer balls have 32 panels, 8 panels, 14 panels and 32 panels. The experimentation used a Kick-Robot which reproduces the same speed and position to repeatedly impact the ball. We attached a dynamometer to this machine in order to measure the impact force. We experimented four pattern of speed: 15m/s, 20m/s, 25m/s, 30m/s. The results suggest that there is any direct correlation between a maximum of impact force and a number of panels. But, when the Cafusa is compared with other balls, the impact force of Cafusa has a lower than any other balls because of the soft material surface. In addition to this, under the all speeds, the impulse value of Jabulani always shows the biggest value compare with other balls. We suggest that Jabulani has a special structure and a special surface.

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最近のサッカーワールドカップの公式球は，ボール表面を構成するパネルの数やその形などの意匠が大きく変化しており，五角形と六角形の32枚のパネルで構成された従来のサッカーボールとその模様が大きく変わった．また，異なるパネルの数やその向きによってボールに加える空気力が変わり飛翔軌道に大きな影響を与えると報告されている．しかし，サッカーボールの表面形状は，様々な形のボールパネルや縫い目が複雑に組み合わされており，それらのボール表面形状が，サッカーボールの空力に与える影響は，ほとんど不明である．そこで本研究では，異なる表面のデザイン（突起の意匠）で構成された5種類のサッカーボールを製作し，その空力特性を風洞実験で検討を行った．その結果，サッカーボールの表面にある突起の模様によってボールに働く空力特性が大きく変わる事が分かった．本研究により，最新サッカーボールの空力特性の究明だけでなく，今後開発されるサッカーボールの飛翔軌道がある程度予測可能になったと考えられる．

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