大谷翔平投手のスイーパーのAMR-LBMによる空力解析

抄録

Baseball pitchers commonly throw a 2-seam low sidespin rate Slider. Recently, some have started to throw a “Sweeper”, a pitch that includes a gyro-spin with a higher spin rate. A representative example of this is the “Sweeper” thrown by Shohei Otani. We study the aerodynamics of the “Sweeper” by using the Lattice Boltzmann Method with a cumulant collision term for numerical simulation. While the conventional Slider produces a certain side force due to the Magnus effect from the sidespin, it does not generate a vertical lift force. In contrast, the “Sweeper”, which includes a gyro-spin, demonstrates a lift force in both the horizontal and vertical directions due to the asymmetry of the seams. As a result of seam asymmetry, the boundary layer separation points become asymmetrical, the wake region is obliquely lowered, and the ball experiences vertical lift force. The flight trajectory data from Shohei Otani’s pitches show good agreement with our computational results. Our findings underscore the unique aerodynamics of the “Sweeper” and the substantial influence of gyro-spin on both aerodynamics and flight trajectories.