Computational Study of Influences of a Seam Line of a Ball for Baseball on Flows

Article type: Research Article

Authors: Himeno, R.

Affiliations: RIKEN (The Institute of the Physical and Chemical Research), 2-1, Hirosawa, Wako, Saitama, 351-0198 Japan.

Abstract: Flows around a ball used in baseball games are calculated using third-order upwind-difference method with various seam positions determined by two rotation angles. Those are four-seam rotation with an angle: a and two-seam rotation with an angle: b. The computed results of the four-seam rotation are compared with experimental data measured in a wind tunnel and computed drag coefficients qualitatively agree well with experiments. However, lift coefficients do not agree well. The computed results and geometrical symmetry suggest that a supporting rod in the wind tunnel would have strong influence on the accuracy of the measurement. Flow changes in two-seam rotation are also simulated. It is found that the lowest drag force is observed at b=90 and that the value is less than half of the largest drag force at a=30 and 60 degrees. The largest lift force is observed at b=20 degree. In this case, a projection of the seam line on the top causes a large separation while smooth surface without the seam at the bottom dose not separate the flow. A pair of longitudinal vortices are found in the wake, which make wake slant and generate large lift force.

Keywords: wake, baseball, CFD, aerodynamic coefficient, longitudinal vortex

Journal: Journal of Visualization, vol. 4, no. 2, pp. 197-207, 2001