PIV Measurement of a Flying Table Tennis Ball

There are some reports that the Magnus force becomes negative at some situation in wind tunnel test. If so, there is possibility of a variety of curves using change of the direction of the Magnus force. PIV measurements of a flying table tennis ball were conducted to confirm whether a similar phenomenon was observed in real flight. A high-speed camera with a frame rate of 10k fps was used to capture the instantaneous flow field of the flying ball. The imaging region was 210 mm × 210 mm. The Reynolds number was approximately 6.5 × 104, which corresponds to a smash in table tennis. A coordinate transformation of the ball's fixed coordinate system captured the wake motion of non-rotating and rotating balls. In the non-rotating condition, the averaged velocity field of the ball was observed to be symmetric, whereas, in the rotating condition, it was asymmetric, which shows the Magnus effect. At spin parameter is 0.65, the Magnus force becomes zero to indicate the appearance of the negative Magnus force. These observations quantitatively agree with the wind tunnel test.