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

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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