SHEAR-LAYER VORTICES AND LONGITUDINAL VORTICES IN THE NEAR WAKE OF A CIRCULAR-CYLINDER

Results are presented on (1) the shear layer vortices developing in th e free shear layers located between the separation point and the first shed Strouhal vortex of a circular cylinder and (2) the longitudinal vortices developing in the braid region of the Strouhal vortices in th e wake. Evidence based on flow visualization shows that the longitudin al vortices develop independently at low Reynolds numbers. An analysis is developed to show that the spanwise length scale of the longitudin al vortices in the separated shear layers and the longitudinal vortice s in the Strouhal vortices are comparable near Re approximate to 1000. At higher Reynolds number, with increasing Re, the spanwise scale of the former reduces faster than that of the latter.