Vortex formation from a cylinder with unsteady surface injection

Vortex formation from a cylinder with unsteady surface injection. Jets from an arrangement of very small holes in the pattern of a three-start helix provide three-dimensional, unsteady surface perturbations. Visualization of the wake structure at the plane of symmetry yields the instantaneous images of positive (red) and negative (yellow) vorticity at two extreme values of momentum Cmu. At the low value of Cmu = 0.02, the classical Karman vortex formation is altered such that a layer of vorticity wraps back towards the base of the cylinder. These layers, which exhibit small-scale Kelvin-Helmholtz concentrations of vorticity, are nearly mirror images of each other, i.e. pi out-of-phase, during the suction and blowing strokes. In contrast, at the higher value of Cmu, the layers of vorticity attach along the base of the cylinder during the suction stroke, whereas during the blowing stroke, they detach at a relatively large angle, i.e. approximately 120°, from the forward stagnation point and form large-scale clusters of positive and negative vorticity, which show a nearly symmetrical pattern. Re = 10,000. [14]