Study about relation between fineness ratio dependency on drag of magnetically suspended axial cylinders and their wake structure

本研究利用日本宇宙航空研究开发机构拥有世界上最大低速风洞试验段的60 cm磁悬浮天平系统，测量了不同长细比的轴向圆柱的阻力系数。此外，还研究了尾流结构与尾流阻力的关系。得到的圆柱体的长细比从4到8的阻力系数显示独立的雷诺数从50000到10000基于模型直径。模型上的边界层在前缘分离流的再附着点的下游是湍流的。阻力系数取决于长细比这一事实主要是由再附着点下游在模型上发展的湍流边界层引起的粘性摩擦阻力的变化。结果表明，在长细比为1.2 ~ 4.0范围内，阻力系数最小， ...更多信息 最小阻力系数范围为1.6至1.7。最小值看起来肯定比公布的小，小于0.8。但是，由于海崖体的阻塞效应无法评估，我们不能指出一个值。在无支架干扰的情况下，采用无线技术对气缸底压进行了测量。结果表明，阻力系数最小时底压系数最大;对测量的压力波动的FFT分析也显示出明确的峰值。此外，我们还观察到轴向圆柱尾迹截面上的涡心在瞬间以非轴对称的方式运动。由于采用了磁悬浮天平系统，观测过程中没有任何支撑物的干扰。本研究中的流动对支撑系统非常敏感，而磁悬浮层测量是此类测试的理想方法。少

In this study, drag coefficients of axial cylinders with various fineness ratios were measured with the 60cm magnetic suspension and balance system at Japan Aerospace Exploration Agency which has the largest test section of low speed wind tunnel in the world. Besides, relation between the drag and wake structure dependency on its fineness ratio was also investigated. Obtained drag coefficients of the cylinders with fineness ratio ranged from 4 to 8 showed independent of Reynolds number from 50000 to 10000 based on model diameter. The boundary layer on the models are turbulent downstream the reattachment point of the separated flow at its leading edge. The fact of that drag coefficient depends on fineness ratio mainly causes the change of viscous friction drag by the turbulent boundary layer developed on the model downstream the reattachment point. We found that the drag coefficient gets its minimum value with respect to the fineness ratio from 1.2 to 4.0 and that the fineness ratio of … More the minimum drag coefficient ranges from 1.6 to 1.7. The minimum value looks smaller definitely than the published one and it is less than 0.8. However, we cannot point out one value because of blockage effect of bluff body which cannot be evaluated. We also measured base pressures of the cylinder with wireless technology without any support interference. The results showed that the base pressure coefficient gets its maximum value when the drag coefficient gets its minimum value. FFT analysis of the measured pressure fluctuations also showed definite peaks. Besides, we observed that centers of vortices on the axial cylinder wake cross sections move in non-axial-symmetric way instantaneously with PIV measurements. The observations were carried out without any support interference because we used the magnetic suspension and balance system. The flow in this study will be very sensitive on support systems and Ply measurement with the magnetic suspension is an ideal way of such kind of tests. Less