ON THE SPANWISE CORRELATION OF VORTEX SHEDDING FROM A CIRCULAR-CYLINDER AT HIGH SUBCRITICAL REYNOLDS-NUMBER

The three-dimensionality of the vortex shedding from a circular cylind er at high subcritical Reynolds number (4.3 X 10(4)) has been studied, focusing on the characteristics of the vortex shedding phase drift an d correlation along the cylinder span. Short time integration of the c orrelation coefficient, based on eight shedding cycles, showed that th ere were strong oscillations in the degree of correlation of the vorte x shedding, and that these oscillations showed strong regularity havin g periods around 10-20 times the Strouhal period. These oscillations s tarted when exceeding separations of DELTAz/d almost-equal-to 1 betwee n the measurement points, and remained up to the largest case studied (DELTAz/d = 6). The phase drift angle between two points at different spanwise positions was analyzed, showing that at the transition separa tion (DELTAz/d almost-equal-to 1) the probability distribution changed from being narrow banded to become more broad banded and closely Gaus sian for an intermediate spacing of 2 < DELTAz/d < 4, and almost unifo rm for DELTAz/d = 6. For all different separations studied (0.25 < DEL TAz/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.