Free flight flow measurements of baseballs

Taylor Naoto Tosaya

In 2015 Major League Baseball observed the home run rate rising unexpectedly, prompting an investigation. The analysis concluded the most likely cause of the home run rate increase was due to reduced drag on the balls. To examine the drag reduction, this work measured the drag on balls pulled from play to find balls with large drag differences to compare. It was hypothesized that small surface and geometrical differences between the higher and lower drag balls caused the drag reduction and this could be visualized in the flow near the surface. Due to the complexity and variation of baseball testing, numerical methods were not used. Particle Image Velocimetry was used to quantify and analyze the flow around balls during still air flight. Still-air drag testing showed spinning balls had drag differences of over 20%, without spin the difference was neglectable. It was found that the orientation of the seams relative to the direction of travel affected the drag of the ball and could increase the drag by nearly 100%, displaying seams as a dominant factor in ball drag. Balls were measured and found to have neither surface flaws, deformations, nor geometric differences such as seam heights. Higher and lower drag ball groups had a less than 8% difference in seam height which has been shown to have less than a 6% difference in carry distance ruling out seam height as the primary factor. Two-dimensional Particle Image Velocimetry quantified the flow of the air near the balls. The point of flow separation, along with the size and intensity of the wake, were measured. There were no significant differences in the point of separation location nor wakes of higher and lower drag balls, dismissing differences in ball surface as a principal factor. It has been presented that the drag reduction was not caused by surface or seam height differences but little more is known about the causes of the drag difference. A strong correlation of seam orientation to drag has been found. Future work will focus on the orientation drag profiles for extreme high and low drag balls.

Free flight flow measurements of baseballs

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