March 23, 2021
Tokyo Institute of Technology
Kyushu University
Keio University
A joint research team from the Tokyo Institute of Technology, Kyushu University, and Keio University, led by Principal Investigator Professor Takayuki Aoki of the Global Scientific Information and Computing Center at the Tokyo Institute of Technology, conducted a detailed numerical fluid simulation of a baseball, including the rotation of its seams. The simulation was performed on the center's supercomputer TSUBAME 3.0 as part of the HPCI System Research Project "Aerodynamic Analysis of a Rotating High-Speed Baseball," which was selected in fiscal year 2020. The results revealed for the first time that for a ball with a two-seam rotation, a "negative Magnus effect" occurs within a certain range of seam angles, which is a major factor causing the drop of a forkball, a type of low-spin two-seam pitch. A comparison between a two-seam and a four-seam pitch, both at a speed of 151 km/h and a rotation rate of 1,100 rpm (revolutions per minute), revealed that the difference in seams alone created a 19 cm difference in the ball's drop as it reached the batter, despite the identical speed and rotation rate.
A forkball has backspin, so it should follow an upward trajectory due to the Magnus effect. However, it is known to take a trajectory close to a parabola with almost no lift, and the reason for this has remained a mystery.
For a smooth sphere, a downward force known as the "negative Magnus effect" had been confirmed under specific conditions in both actual measurements and simulations, but it was thought not to occur with a seamed baseball. Furthermore, while measurements with high-speed cameras can determine changes in trajectory and speed, they could not reveal what kind of aerodynamic forces were acting on which parts of the ball, nor how those forces changed over time.
The results of this research are based on a presentation given at the Japan Society of Mechanical Engineers Symposium: Sports Engineering and Human Dynamics 2020, held in November 2020, and include significant data obtained since then.
For the full press release, please see below.