1986-10-01

Coherent Shedding from a Circular Cylinder at Critical, Supercritical, and Transcritical Reynolds Numbers 861768

The flow around a circular cylinder is a classical problem of fluid dynamics, and its study is of great importance since the cylinder is one of the most commonly occuring shapes in engineering structures. The current experimental investigation examines both the mean drag and the unsteady flow parameters (in the form of a nondimensional eddy-shedding frequency) at critical, supercritical, and transcritical Reynolds numbers (Re > 3 × 105).
The tests were conducted in the NASA Langley Low Turbulence Pressure Tunnel over a Reynolds number range of 2.5 × 105 to 6.2 × 106 and a Mach range of 0.05 to 0.40. The unsteady flow phenomena was measured in the wake and on the test section walls with miniature pressure transducers. The determination of the Strouhal number in the supercritical regime was complicated by the presence of broadband signatures in the frequency domain. Interpretation of data in this regime was accomplished by correlating the unsteady lift force with the fluctuating pressure measured by probes mounted in the wake. This technique proved to be an effective means for determining shedding frequencies.
The results follow general trends established by previous investigators with the measured Strouhal number jumping discontinuously from St ≃ 0.2 to St ≈ 0.43 in the supercritical region. Low values of the Strouhal number in the supercritical regime were recorded, the lowest being 0.117. Strouhal number of this low magnitude are generally not reported in the published literature, but the levels do agree with those in at least two separate investigations.

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