Shear Layer Vortices and Longitudinal Vortices in the Near Wake of a Circular Cylinder

J. Soria Department of Mechanical Engineering, Monash University, Clayton, Australia • Results are presented on (1) the shear layer vortices developing in the 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 the wake. Evidence based on flow visualization shows that the longitudinal vortices develop independently at low Reynolds numbers. An analysis is developed to show that the spanwise length scale of the longitudinal vortices in the separated shear layers and the longitudinal vortices in the Strouhal vortices are comparable near Re = 1000. At higher Reynolds number, with increasing Re, the spanwise scale of the former reduces faster than that of the latter.