Vortex shedding from spheres

Abstract

Vortex shedding from spheres has been studied in the Reynolds number range 400 < Re < 5 × 10 6 . At low Reynolds numbers, i.e. up to Re = 3 × 10 3 , the values of the Strouhal number as a function of Reynolds number measured by Möller (1938) have been confirmed using water flow. The lower critical Reynolds number, first reported by Cometta (1957), was found to be Re = 6 × 10 3 . Here a discontinuity in the relationship between the Strouhal and Reynolds numbers is obvious. From Re = 6 × 10 3 to Re = 3 × 10 5 strong periodic fluctuations in the wake flow were observed. Beyond the upper critical Reynolds number ( Re = 3.7 × 10 5 ) periodic vortex shedding could not be detected by the present measurement techniques. The hot-wire measurements indicate that the signals recorded simultaneously at different positions on the 75° circle (normal to the flow) show a phase shift. Thus it appears that the vortex separation point rotates around the sphere. An attempt is made to interpret this experimental evidence.