Patterns of streamwise vorticity in the near-wake of a cylinder

Patterns of streamwise vorticity in the near-wake of a cylinder. Instantaneous patterns of velocity and positive (red) and negative (yellow) streamwise vorticity in the crossflow plane of the near-wake exhibit: (a) a nearly uniform crossflow, due to drawing of irrotational fluid across the wake durin Karman vortex formation, and embedded concentrations of vorticity having a characteristic spanwise wavelength approximately equal to the cylinder diameter [x/D = 1; Re = 5,000]; (b) a shear flow in the crossflow plane with a larger-scale concentration of negative (yellow) streamwise vorticity where the shear flow changes direction [x/D = 2; Re = 5,000]; and (c) a nearly spanwise uniform crossflow from right to left with embedded concentrations of vorticity, again having a spanwise wavelength of about the cylinder diameter [x/D = 1; Re = 10,000]. Distance x is from the base of the cylinder to the crossflow plane. [7] Similar imaging, obtained via PIV cinematography, is given in [8,9,10,11].