241 Comparison of Traditional Rubber-ball Baseball Ball of Japan and Aerodynamic Characteristic of the Measure League Ball

Abstract

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.