1-m磁力支持天秤装置を用いた回転する球の風洞実験法の開発

抄録

The conditions for the generation of negative Magnus force about a rotating sphere has not been clarified yet. Therefore, we developed a wind tunnel test method to investigate the negative Magnus force region using the 1-m magnetic suspension and balance system of the Institute of Fluid Science, Tohoku University, which can support a model in the wind tunnel test section by magnetic force without a mechanical support. By constructing a sensing and control method and a model structure suitable for a rotating sphere, we obtained a technique to rotate a sphere of about 142 mm in diameter to about 1100 min-1 with magnetic support. By applying this technique to a wind tunnel test, it is now possible to acquire the aerodynamic forces that change from time to time with decay of rotation speed from 560 min-1 in an airflow of 7 m/s. This corresponds to a Reynolds number of about 6.5×105 based on the diameter of the sphere model, and a ratio of the circumferential velocity of the rotating sphere to the mainstream velocity, SP, varying from 0.6 to 0. In the present wind tunnel test, the normal Magnus effect was observed, and in the range of 0.5 < SP < 0.6, a decrease in the positive Magnus force and a behavior like approaching the critical region were observed, but the negative Magnus force was not observed. The aerodynamic force evaluation was limited to qualitative evaluation due to the large fluctuation of aerodynamic force that may be caused by the change of the model outline with rotation and the center-of-gravity misalignment.