A17 ジャイロボールのドラッグクライシス(ボール)

概要

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Using a high-speed video camera, we measured the trajectory and the rotation of a hard baseball thrown by a pitching machine, which can launch a rifle spinning 'gyro-ball'. We determined the drag coefficient by analyzing the video images. The drag coefficient of a 4-seam gyro-ball with the spin parameter (SP)≈0.12, 0.23 and 0.35, decreases gradually with the Reynolds number (Re). In contrast, the drag coefficient of a 2-seam gyro-ball with SP≈0.12 and 0.23 decreases in two steps. For SP≈0.12, it shows sharp decreases in the ranges 0.8×10^5<Re<1.0×10^5 and 2.0×10^5<Re<2.2×10^5 and it attains its minimum at Re≈2.2×10^5. Similarly, for SP≈0.23, the drag coefficient decreases in the ranges 0.7×10^5<Re<1.0×10^5 and 1.7×10^5<Re<1.8×10^5 in two steps, and attains its minimum at Re≈1.8×10^5. For SP≈0.35, it is almost constant below Re=1.3≈10^5 and attains its minimum at Re≈1.6×10^5 These findings confirm the occurrence of the drag crisis of Gyro-Balls. The different Re-dependence is due to the difference in seam patterns.
一般社団法人日本機械学会の論文
2007-11-13