The aerodynamic properties of a spinning table tennis ball have been investigated by flight experiments. Using high speed video-cameras, the trajectory and rotation of an official ball (Nittaku 3-Star Premium), which was launched by a three-rotor-machine, were recorded. The drag and lift coefficients (CD and CLZ) were determined by analyzing the videoimages. The measurements cover the speed (Re) and rotation range (SP) of table tennis shots, i.e., 3.0 × 10 4 < Re < 9.0 × 10 4 , 0 < SP < 1.0, and CD and CLZ are obtained as functions of Re and SP. The lift coefficients CLZ is not a monotonic function of SP. A deep valley of CLZ is found around SP=0.5, and the lift force exerted on a spinning ball almost vanishes at Re = 9.0×10 4 and SP = 0.5. In this valley, the standard deviations of CLZ increase drastically, indicating the occurrence of "Lift crisis".
The aerodynamic properties of a spinning table tennis ball were investigated using flight experiments. Using high-speed video cameras, the trajectory and rotation of an official ball (Nittaku 3-Star Premium), which was launched by a three rotor machine, were recorded. The drag and lift coefficients (CD and CL) were determined by analysing the video images. The measurements covered the speed and rotation range of typical table tennis shots in the form of the Reynolds number (Re) and dimensionless spin rate (SP), i.e. 3.0 × 104 < Re < 9.0 × 104 and 0 < SP < 1.0, and CD and CL were obtained as functions of Re and SP. We determined that the lift coefficient CL is not a monotonically increasing function of SP. A deep valley of CL was found around SP = 0.5, and the lift force exerted on a spinning ball almost vanished at Re = 9.0 × 104 and 0.48 < SP < 0.5. These results qualitatively agree with the results from recent wind tunnel tests, but quantitative differences owing to the unsteady nature of the flight experiments remain. This anomaly in the lift coefficient should be called the ‘lift crisis’.
We have developed a remote and precise feedback control system using optical measurement technology to alter the angle of a flap, which is part of a wind tunnel test model, automatically and to earn the aerodynamic data efficiently. To rectify the wasteful circumstance that Japan Aerospace Exploration Agency (JAXA)’s low-turbulence wind tunnel stops ventilation every time to switch model configurations, we repaired hardware for remote operation and generated software for feedback control. As a result, we have accomplished a system that dramatically advances the efficiency of wind tunnel tests. Moreover, the system was able to consider the deformation of the model through optical measurement; the system controlled flap angles with errors less than the minimum resolution of optical measurement equipment. Consequently, we successfully grasped the nonlinearity of three aerodynamic coefficients C L , C D , and C M p that was impossible so far.
This study scrutinized the aerodynamic change of adding a yaw-wise rotational degree of freedom to a single slotted flap of airplane via computational fluid dynamic analyses. Existing slotted flaps have spanwise constant gaps and are disharmonious with the 3D nature of the flow field. A flap geometry and its angle condition are sensitive to aerodynamic performance; small variations in them must be useful in aerodynamic improvement. To add the yaw-wise rotation to a flap is a lower hurdle than to attain other high-lift systems. Therefore, after defining a simple configuration consisting of a fuselage, a wing, and a single slotted flap, we investigated the mesh dependency to consider the diversity in flow phenomena precisely; we examined the effect of the yaw-wise rotation for the flap on improving the whole lift. To place the flap at suitable yaw-wise rotation angles consequently effected raising the lift. We revealed the physical mechanism that accelerating the fluid in the gap between the wing and the flap changes the separation structure on the flap upper surface and grows the lift.
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