著者
多田 海斗 平塚 将起 伊藤 慎一郎 瀬尾 和哉
出版者
一般社団法人 日本機械学会
雑誌
日本機械学会論文集 (ISSN:21879761)
巻号頁・発行日
vol.89, no.924, pp.23-00045, 2023 (Released:2023-08-25)
参考文献数
15

The paper describes the critical Reynolds number of soccer balls as a function of the total groove volume on the ball surface. In this study, the aerodynamic drag and separation point of 6 soccer balls with different panel orientations were measured in a wind tunnel. Moreover, the total volume of grooves on the ball’s surface was measured by One shot 3D measuring machine. It was found that the drag coefficient in the supercritical region and the critical Reynolds number depend on the design of the ball surface (shape, number of panels, surface roughness). A negative correlation exists between the total groove volume on the surface and the critical Reynolds number. When the total groove volume is large, the drag in the supercritical region increases. The position of the separation point does not change in the subcritical and supercritical regions even if the orientation of the panel is changed. However, when the groove width is wider, the panel orientation dependence becomes significant in the supercritical region. In the transition region, the position of the separation point differs depending on the panel's orientation.
著者
中島 知浩 伊藤 慎一郎 平塚 将起
出版者
一般社団法人 日本機械学会
雑誌
シンポジウム: スポーツ・アンド・ヒューマン・ダイナミクス講演論文集 2017 (ISSN:24329509)
巻号頁・発行日
pp.B-12, 2017 (Released:2018-05-25)

The structure of the current tennis ball is covered with a uniform felt fabric on the outer surface made of hard rubber. The inside of the ball is filled with air about 1.8 atm. The seam is filled with adhesive or resin. The seams are filled with glue or resin. The ball in tennis is always struck with rotation. Rotational speed of the serve ball is about 5,500 rpm maximum. It is up to about 4,700 rpm for the stroke. As the ball continues to hit, the surface felt wears. Also, air leaks out through the structure inside. These factors cause a difference in the aerodynamic characteristics of new and used balls.In general it is a new ball to use in the game, but the one used in practice is a used ball. Worn out changes the hydrodynamic properties of the ball, and the trajectory of the ball also changes. Therefore, the performance difference between the new tennis ball and the used tennis ball should be confirmed by measuring the fluid force.In this research, the aerodynamic characteristics of the old and new tennis balls rotating were investigated and the PIV results of the flow around the ball due to the wear of the felt producing these characteristics. For the four types of tennis balls tested, used balls showed higher in drag coefficient than new balls, and new balls tended to be higher than used ball in lift coefficient. It is believed that deformation due to deterioration of ball rubber brings about a change in drag coefficient, which causes a change in lift coefficient due to wear of the surface felt. In the new ball, feltfluff stands, which indicates that the wake flow is large and inclined diagonally backward compared to the used ball, and the air around the ball is found to be caught by the felt fluff.