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

Summary

Flows around a baseball without rotation are calculated using third-order upwind-difference method with various seam positions determined by two angles in orthogonal two directions. Those are four-seam rotation direction with an angle: α and two-seam rotation direction with an angle: β. The computed results in the four-seam rotation cases 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 direction are also simulated. It is found that the lowest drag force is observed at α = 90 and that the value is less than half of the largest drag force at α = 30 and 60 degrees. The largest lift force is observed at α = 20 degree. In this case, 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.