著者

青木 克巳 武藤 浩司 岡永 博夫

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B編 (ISSN:18848346)

巻号頁・発行日

vol.77, no.775, pp.793-802, 2011 (Released:2011-03-25)

参考文献数

15

被引用文献数

1

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The present study clarifies the effects of dimples for drag and lift on a sphere with rotation. The sphere with dimples has 328 arc type dimples on its surface uniformly. The present study measures velocity distribution in wake and pressure distribution on a sphere surface, and visualizes flow around a sphere by the spark tracing method for the case in which Reynolds number Re=0.4×105-1.3×105. For the case of a smooth sphere, separation point on deceleration side shifts downstream remarkably as spin rate ratio (circumferential velocity of a sphere / free stream velocity) increases. The pressure distribution on deceleration side decreases compared to that on acceleration side. The wake becomes small and shifts opposite direction of rotation. Therefore, the drag reduces, and the lift becomes negative. For the case of a sphere with dimples, this phenomenon occurs for the case in which critical Reynolds number Re=0.5×105. The separation point on acceleration side shifts downstream, and the separation point on deceleration side shifts upstream as spin rate ratio increases for the case in which super critical Reynolds number Re=1.3×105. The pressure distribution on acceleration side decreases compared to that on deceleration side. In addition, the pressure distribution on outside dimple decreases compared to that on inside dimple. The wake becomes large and shifts direction of rotation. Therefore, the drag and positive lift increase.

著者

森山 幸平 岡永 博夫

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.23-00083, 2023 (Released:2023-08-25)

参考文献数

16

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The surface of a golf ball is provided with innumerable dents called dimples to improve the flight distance. In this study, we manufactured 15 model balls in which the dimple occupancy and the dimple volume ratio was changed by the dimple diameter and the number of dimples, and the dimple shapes. Using these balls, we carried out lift and drag measurements of the rotating balls in wind tunnel experiments. Then, a flight trajectory simulation was performed based on the obtained experimental results. As a result, the influence of the base shape showed different results for both drag and lift coefficients for each occupancy. However, the drag coefficient decreased and the lift coefficient increased as the dimple volume ratio increased regardless of the dimple shape. In addition, the relationship between the lift-drag ratio and the dimple volume ratio showed that the lift-drag ratio decreased as the dimple volume ratio increased. The flight trajectory simulation results showed that the flying distance was greater for O=52.6% and O=63.1% with a conical base when the dimple volume ratio was small and the dimple depth is DD/d=4.55×10-3. Two spheres with a spherical base and a conical base at O=83.1%, also exhibited similar flying distances. However, the flight distance tends to increase as the dimple volume ratio decreases. The ball's trajectory was lower when the volume ratio was small, and higher trajectory was obtained when the occupancy ratio was high.

著者

青木 克巳 岡永 博夫 長瀬 二郎

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

巻号頁・発行日

vol.2013, pp._241-1_-_241-10_, 2013

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In this report, aerodynamic characteristic such as lift and drag of official rubber-balls used in the game of the baseball are studied experimentally. And the aerodynamic characteristic of these rubber-ball is compared and is examined with the aerodynamic characteristic of smooth sphere and sphere with dimple and the Major League ball. In addition, the aerodynamic characteristic for seam angle and spin rate ratio ratioα (=V/U, V: peripheral velocity of test balls, U: flow velocity)is also clarified. And, the flow pattern around the test balls are visualized by the spark tracing method. Following conclusions were got from these results. (1) The dimpled rubber-ball has a critical region where the drag coefficient decreases in the same way as the smooth surface balls. (2)Depending on the surface structure of test balls, the aerodynamic characteristics differ significantly. When dimples are added to the balls with seams, the critical region moves toward the lower Reynolds number side, but the minimum drag coefficient increases. (3)About the rubber-ball and Major League ball, C_D shows the almost same values without rotation. However at the rotational state, C_D of the Rubber-ball is lower than that of the Major League ball . (4)The values of C_D take different values depending on type A〜E and become large as α increases. The values of C_L stand in a same line which rises as α increase.