A37 サッカーのストレートボールにおける渦構造の検討(サッカーボールの飛翔特性)

抄録

The vortex structure behind an actual soccer ball in real flight is not clear either in the near-wake or the far-wake, although it is speculated that the vortex structure greatly determines the trajectory and dynamics. We analyzed the vortex shedding characteristics and far-wake structure of a straight soccer ball when slowly spinning (<12.56 rad s^<-1>) in flight under realistic conditions. Two high-speed (1000 fps) video cameras and a smoke-generating agent were used for trajectory tracking and flow visualization, respectively. The cameras were placed midway between where the ball was placed and the soccer goal. The vortex shedding frequency determined from wide-angle images afforded a Strouhal number (St) estimate of about 0.6. The vortex structure behind the soccer ball at supercritical Reynolds numbers (Re) might comprise distorted loop vortices seen behind a smooth sphere at 3.8 × 10^5 < Re < 10^6 (Taneda, 1978). Large-scale undulations were not observed in the vortex trail behind the straight balls once airborne.