On the spanwise correlation of vortex shedding from a circular cylinder at high subcritical Reynolds number

Abstract

The three-dimensionality of the vortex shedding from a circular cylinder at high subcritical Reynolds number (4.3×104) has been studied, focusing on the characteristics of the vortex shedding phase drift and correlation along the cylinder span. Short time integration of the correlation coefficient, based on eight shedding cycles, showed that there were strong oscillations in the degree of correlation of the vortex shedding, and that these oscillations showed strong regularity having periods around 10–20 times the Strouhal period. These oscillations started when exceeding separations of Δz/d≊1 between the measurement points, and remained up to the largest case studied (Δz/d=6). The phase drift angle between two points at different spanwise positions was analyzed, showing that at the transition separation (Δz/d≊1) the probability distribution changed from being narrow banded to become more broad banded and closely Gaussian for an intermediate spacing of 2<Δz/d<4, and almost uniform for Δz/d=6. For all different separations studied (0.25<Δz/d<6), the probability distribution of the phase drift angle had a zero mean, indicating that the vortex shedding was, on the average, parallel to the cylinder.