Numerical simulation to reproduce trajectories of rotating baseball

Abstract

In baseball, there are many different types of balls thrown by pitchers. The changes in trajectory and velocity have a big impact on a game. In general, the trajectory of a ball depends on three factors: spin rate, an axis of rotation, and velocity. On the other hand, some trajectories cannot be explained by only 3 parameters, such as knuckleball behavior and two seam-fastball drop-offs. In this study, we have reproduced trajectories of rotating baseballs by using CFD analysis and evaluate the effect of seams on the ball on aerodynamics and movement of the ball. For the fluid computations around the baseball, we used a simulation code based on Cumulant-LBM. To evaluate the validity of the turbulence computation in the high-Reynolds number regime, we have reproduce the drag crisis and the negative Magnus effect. Firstly, fluid calculations were carried out for two different four seam pitches with different rotation rates. We have confirmed that the magnus effect has become larger and the trajectory changed as the rotation speed increased, as the rotation speed increased. Next, we have performed CFD analysis under two conditions where the velocity, rotation speed, rotation angle were equal and only the position of seams were different. We have found the relationship between seams and ball trajectory by checking trajectories. It is concluded that the two trajectories were very different, and the influence of seams on the aerodynamic characteristics and ball behavior.