Invited Speakers

Shinichiro Ito (Kogakuin University)

PIV reveals surface roughness reduction with micro dimples in dimples of a golf ball.

Title: Applications of high-speed imaging to sport dynamics
Author: Shinichiro Ito
Affiliation: Professor, Kogakuin University
Email: ito[at]cc.kogakuin.ac.jp
URL: http://fluid.mech.kogakuin.ac.jp/~ito/

Fig. 1 Scales on a butterfly wing; and skin hairs of a bee

Fig. 2 An image of the experimental setup

Fig. 3 Surface velocities at a top of golf balls with (a) and
without (b) improved dimples and micro dimples in dimples

Butterflies have scales on their wings, and bees’ bodies are covered with tiny hairs. All these micro devices help them fly freely and swiftly (Fig. 1). Why are there no such structure on the surface of a golf ball? PIV reveals surface roughness reduction with micro dimples in dimples. An experimental set-up was developed to capture a motion image of a turbulent flow field around a rotating golf ball. A shaft penetrating a golf ball is firmly fixed in a wind tunnel and rotated (Fig. 2).. The wind speed was 29 m/s, the rotation speed was 2,400 RPM, and thus the spin ratio was 0.186. The flow field close to a golf ball was visualized with a telephoto lens and PIV. The frame rate and the frame count of the high-speed video camera were 2,000 fps and 5 Mpixels. The pulse width and the peak-pulse power of each of the double-pulse YAG lasers for sheet illumination were 100 ns and 2 kW. The PIV was applied for 32 x 32 windows with a Fourier-transformed correlation method. Improvement of the dimple configuration and the micro dimples in the dimples clearly decreases the surface roughness and increases the flow velocity at a thin layer of the top of the ball as shown in Fig. 3.
Biographical Sketch: Shinichiro Ito was graduated from Department of Mechanical Engineering of the University of Tokyo in 1979, and from the Graduate School of the same university in 1986. After he worked for National Defense Academy of Japan from 1986 to 2009 as Associate Professor, he moved to Department of Mechanical Engineering of Kogakuin University as a Professor.  He also stayed at Department of Aerospace Engineering of Pennsylvania State University as a visiting researcher from 1989 to 1991. His research interest is mainly interaction of living things and fluid motion, such as sport science/engineering and aero-aqua biomechanics. He is a recipient of many scientific awards for his contributions to these scientific and engineering fields, including the Frontier Award of the Japanese Society of Mechanical Engineers. He often appears on scientific TV programs as a commentator, and is chairing many committees on sport- and bio-engineering.