On critical flow around smooth circular cylinders

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Abstract
The characteristics of the flow around a smooth circular cylinder in the critical Reynolds-number range have been investigated experimentally on the basis of instantaneous mean-pressure-distribution measurements on the cylinder and of hot-wire velocity-fluctuation measurements in the cylinder wake. Two subregions have been identified in the critical or lower transition; the first characterized by symmetric pressure distributions, intense vortex shedding, and gradual and significant variations in characteristic parameters as the Reynolds number increases, and the second by intense flow oscillations associated with formation and bursting of laminar-separation bubbles on one or both sides of the cylinder, without preference for side. The spectra of the velocity fluctuations in the second, unsteady subrange appear in general with broad band peaks. The spectral peak in the twin-bubble regime which follows this second subrange is sharp but has little energy compared to subcritical peaks.