Taketo MIZOTA’s research while affiliated with Fukuoka Institute of Technology and other places

Aerodynamics of spinning golf balls were investigated by Wind Tunnel Test and Computational Fluid Dynamics at the wind speed of 25 and 40 m/s. For CFD analysis, turbulence model (k-ω SST) with transition γ-model was applied. As for both methods, a golf ball with shallower dimples has higher CL at U=40m/s while drastic reduction in CL was confirmed at U=25 m/s and Sp =0.1. The increase in CD as with the decrease in Sp was also confirmed at this CL reduction phase. It seems that the flow around golf ball changes from turbulent to laminar as with the decrease in Sp. Visualization of CFD results indicates that the separation point of the shallower ball upper side shifts forward for the condition of U=25m/s and Sp =0.1 compared with the other conditions.

Aerostatic bearing load cell which is available to measure 3-components aerodynamic forces and torque is developed. Each table to detect the forces is floating by air pressure and balanced by a pair of coil springs. The model in the wind tunnel is connected with fine piano wires to a light frame on the unit. The wind loads acting on the model shift the each table within short distances. These shift magnitudes are measured with laser displacement devices. Aerodynamic torque is counted by spinning decay ratios of the model. As a result, this load cell has some specific characteristics to measure the forces, such as good linearity, high resolution, less interference and less temperature drift. The validity of this new apparatus is shown by the aerodynamic forces and torque measurements on highly spinning golf ball.

Aerodynamic forces act on a golf ball during flight. For that purpose in order to develop a golf ball with high performance, it is important to analyze aerodynamic characteristics of the golf ball. On the other hand, dimple pattern of a golf ball is complicate and the influence of dimples hasn’t been investigated in detail. Therefore the influence of golf ball dimples on aerodynamic characteristics was investigated using a wind tunnel and rotating device. Some golf balls whose dimples have different depths were measured. As a result, it was found that the shallower the dimple was, the larger the lift coefficient was. However, when the depth of the dimples was much shallower, the lift coefficient was extremely-little on the slow velocity, i.e. under 30m/s. When the golf ball trajectory which was launched with a driver was calculated under various initial conditions, the ball velocity became under 30 m/s over the vertex of the trajectory in many cases, including professional male golfers and female golfers. Therefore, if the lift coefficient of the velocity of 30m/s becomes smaller, distances will become shorter. Dimple patterns that had a high lift coefficient at all velocities was researched. As a result, it was found that a golf ball with a dimple pattern that has extremely small dimples between large shallow dimples has a high lift coefficient at all velocities, including under 30m/s. In order to investigate the cause of the results, a flow visualization experiment was conducted. Visualization of flow around a golf ball was conducted by generating smoke. Moreover pictures of flow were taken by high-speed video and analyzed by PIV (Particle Image Velocimetry). As a result, there was the difference in the streamline distribution between golf balls.

Aerodynamic characteristics of some golf balls whose dimples have different depths were measured. As a result, it was found that the shallower the dimple was, the larger the lift coefficient was. However, when the depth of the dimples was much shallower, the lift coefficient was extremely-little on the slow velocity, i.e. under 28m/s. We searched for a golf ball with dimple patterns that had a high lift coefficient at all velocities. As a result, it was found that a golf ball with a dimple pattern that has extremely small dimples between large shallow dimples has a high lift coefficient at all velocities, including under 28m/s. In order to investigate the cause of the results, a flow visualization experiment was conducted. Visualization of flow around a golf ball was conducted by smoke wire method. Moreover pictures of flow were taken by high-speed video and we analyzed them by PIV (Particle Image Velocimetry). As a result, there was the difference in the streamline distribution between golf balls.

PIV methods coupled with smoke wire techniques have been studied. The wire arrangements of these methods were perpendicular to the wind tunnel flow until now, however in our new proposal, the arrangements are parallel to the main flow direction of wind tunnel. The former wind speed, which was available to the flow observation, had been restricted only 0〜4.0 m/s. But, according to our new method, the maximum wind speed was ranging 40 m/s with 1 second duration time of smoke, which is available to the image captures by high speed camera of 20000 fps. The increase of wake turbulence behind these wires were measured by PIV method itself. We showed some examples of stream line measurements behind spinning golf balls and baseball balls under 40 m/s wind speed.

Wind tunnel experiments were conducted to study the aerodynamic characteristics of the spinning soccer balls with variously oriented spinning axes, of which balls are observed in a real game. Ball suspension apparatus with the piano wire strings and a shaft-bearing system through a soccer ball are studied with the cautions to obtain good linearity of spring support, non-interference to the other independent directions and the higher natural frequency of the system. The smooth rotation of a ball was accomplished with well spinning technique of dynamic balance. The 3-components aerodynamic forces of spinning ball in the fundamental arrangement of the axis are reported with the flight path calculations compared with ball flight observation.

An air suspended load cell, which is available to measure steady aerodynamic forces on the spinning golf ball in the wind tunnel flow, has been developing during these five years. The characteristic to measure two components of forces as drag and side ones had already been accomplished with sufficient accuracy. However, the performances of the lift force direction had not been achieved by the influences of atmospheric pressure changes. The sufficient accuracy has accomplished, in this study, mainly by two improvements of the light-weight of ball supporting unit and the cancellation mechanism of atmospheric pressure variations. The lift force on highly spinning golf ball in the wind tunnel flow are measured and compared with the results of gauge type load cell.

Wind tunnel experiments were conducted to study the aerodynamic characteristics of the spinning baseball ball with variously oriented spinning axes, of which balls are observed in a real game. Ball suspension apparatus with the piano wire strings and a shaft-bearing system through a ball are studied with the cautions to obtain good linearity spring support, non-interference to the other independent directions and the higher natural frequency of the system. The smooth rotation of a ball was accomplished with well tuning technique of dynamic balance. The 3-components aerodynamic forces in the 4-seam arrangements of the axis are reported with the variations of pitching and yawing angles. Ball trajectory calculations were also reported using these aerodynamic characteristics.

According to the observations of pitched ball in real baseball game and aerodynamic characteristics clarified by wind tunnel experiments, there are many strange changing ball in baseball ball. In this research, special attention was focused on spinning axes direction, which oriented toward boll flight direction. There are no convenient pitching machines to be able to generate such kind of balls, easily. We had developed a pitching machine with pressurized air method into higher functional one, in which be able to generate purely oriented toward boll proceeding direction, with 2 and 4-seams ball arrangements. In this reports, we describe the strange characteristics of such kind of balls, and then some trial developments of the pitching machine. High speed camera images of shooting balls of 2 and 4-seams balls showed the success in this idea.

We have measured drag coefficients of a sphere and a circular cylindrical aerodynamic model using a five axes and a six axes control magnetic suspension and balance system (MSBS) developed by us. This MSBS has the characteristics of large aperture relative to the weight, light weight, and small electric power consumption in comparison with the conventional ones. We had good agreements between the measured values of the drag coefficient and the values appearing in the common aerodynamic handbook or textbook. We also succeeded in measuring the aerodynamic influence of a supporting rod of the aerodynamic models making use of the characteristics of the MSBS. Conventionally, the MSBS can be used only in large scale laboratories because the size, weight, and electric power consumption are large. We think that successful measurements of various aerodynamic characteristics using this type of MSBS will stimulate the introduction of it into the wind tunnel experiments in small scale laboratories.