Separated flow around a rotating gyroball |
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Authors: | Koju Hiraki Kota Ishitsu Keisuke Yamada |
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Institution: | (1) Kyushu Institute of Technology, Kitakyushu, Japan |
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Abstract: | Abstract In baseball, a gyroball is known as a pitched ball which has its rotation axis oriented towards the catcher, i.e., in flight
direction, and therefore does not create a lift force. The purpose of this study was to clarify what effect the seams of such
a rotating gyroball have on the drag force acting on the ball. Two typical seam patterns, one with two and one with four seams,
were selected. First, pitching experiments were carried out to capture the trajectories of various breaking balls. From the
obtained trajectories the drag coefficients were estimated. Flow visualization was applied to a heated flying gyroball with
the help of the schlieren technique to investigate the flow separation area. To verify the results obtained in the pitching
tests, corresponding wind-tunnel experiments were also conducted with a device which allowed the ball to rotate freely in
the tunnel. Drag measurements and flow visualization by fog were performed on a rotating gyroball. Both in the pitching and
wind-tunnel tests, the drag coefficient of the two-seam gyroball was smaller than that of the four-seam one by 0.04 or approximately
13%. The flow visualization revealed that the flow-separated area of the two-seam gyroball was smaller due to flow reattachment
made possible by a more energetic boundary layer. This observation can well explain the drag difference between two- and four-seam
gyroballs. |
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