Data from: Seam Shifted Wake in the Magnus and non-Magnus Directions


An experiment was conducted to investigate the Seam Shifted Wake effect in the Magnus and non-Magnus directions. Previous studies indicate the location of seams can alter wake formation and create forces acting on a ball due to a difference in pressure. The impact on movement was as expected in the non-Magnus direction, but studies show a SSW effect in the Magnus direction as well. Particle Image Velocimetry was used in this study to analyze the boundary layer separation points of air flow around an official MLB ball in flight. Data was collected for non-rotating baseballs with a range of seam orientations and velocities of 60, 90, and 110 MPH, and for rotating baseballs with a velocity of 90 MPH and rotation rates of 1300, 1800, and 2300 RPM. Boundary layer separation maps were created to compare the non-Magnus baseball cases and the rotating baseball cases as well as the separation point of a smooth ball at the same velocity and rotation rates. The results of the non-rotating baseball cases show the SSW effect varies with Reynolds number. The results of the rotating baseball study show seams can act to advance the separation point or delay the separation point past the natural separation point of the turbulent boundary layer. This results in a SSW effect that can add to or subtract from the Magnus effect.

Author ORCID Identifier

Barton Smith

Document Type




File Format


Viewing Instructions


Publication Date



Utah State University


A two-component planar Particle Image Velocimetry (PIV) system is used to generate the air velocity vectors around baseballs in the plane parallel to the flow. The LaVision software shows the (x,y) location of the cursor in the image frame of each dataset. The coordinates of the center of the ball in the image is computed using the y-coordinate of the top- and bottom-most points and the x-coordinate of the left- and right-most points of the ball in the image. The angle between any point and the hemisphere plane is then computed using trigonometric functions. The angle from the hemisphere plane of the seams on the ball and the boundary layer separation point on the top and bottom of the ball is computed. The position of the seams is found using the raw PIV images. This location is defined as the point where the two leather pieces on the ball meet. This is easily identified as the center of the "m-shape" of the seams. The processed PIV images were analyzed to determine the separation point of the flow. This is where either a velocity vector is located normal to the surface of the ball, or two velocity vectors are pointing in opposite directions. This is more easily recognized by large vorticity values near the ball surface. The raw data was analyzed as a safeguard for potential poor masking to confirm the separation point found analyzing the processed data. The positions of the seams and the separation points were recorded in the Results CSVs. Both the 4-seam and 2-seam data for each study are found in the following CSVs:

Note the location of the seams and the separation point was repeatable within 0.74° at 95% confidence.

Referenced by

Garrett, J. W., “Seam Shifted Wake in the Magnus and non-Magnus Directions", MS Thesis, Utah State University, 2022.



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Aerospace Engineering | Mechanical Engineering


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This work is licensed under a Creative Commons Attribution 4.0 License.




Additional Files

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Results_90_1300.csv (17 kB)
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Results_90_1800.csv (16 kB)
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Results_90_2300.csv (15 kB)
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Vector (17594133 kB)
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README_Garrett.txt (6 kB)
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