Unsteady drag measurements for flow over a circular disk

Unsteady drag measurements were conducted in a low speed wind tunnel to investigate the drag of the circular disk which was normal to the flow. The circular disk was interfered by an upstream two-dimensional rod in the horizontal symmetry plane of the disk in the Reynolds number range from 0. 44 × 10 to 2. 74 × 10~5 based on the disk diameter. The results indicate that the mean drag coefficient of the circular disk does not depend on the Reynolds number which was tested in present study, no matter there is an interference rod upstream of the circular disk or not. Meanwhile, the interference rod leads to decrease of the mean drag coefficient and increase of the drag fluctuation of the circular disk. The increment value of the drag fluctuation increases rapidly, when the Reynolds number is beyond 1. 84 × 10~5. By the frequency analysis, the dominate frequency of the disk drag without the interference rod corresponds to the antisymmetric fluctuation frequency induced by the helical vortex structure (the Strouhal number is 0. 135).