On the wake of a circular cylinder with nodal and saddle attachment

Flow field of a cylinder with a mid-span curvature was experimentally investigated in a wind tunnel and a water tunnel. The azimuthal orientation of the cylinder was changed to obtain a nodal, saddle and a mixed nodal–saddle type of flow attachment. Surface flow topology suggested that the nature of the attachment strongly influenced the spanwise distributions of foci structures that play a significant role in introducing three-dimensionality in the immediate wake. Flow visualization in the water tunnel revealed that the length of a vortex formation region also followed the changes in the nature of the attachment. A symmetric shedding of vortices was observed with a saddle type of attachment. Wake mean velocity profiles showed that the velocity defect and therefore the drag of a curved cylinder was minimum for nodal, and maximum for saddle type of attachment. Nomenclature of the wake was compared with asymptotic profiles and equilibrium parameters. Approach to self-preservation, similarity and other features are discussed.