Abstract
The flowfield produced by a vortex pair approaching a circular cylinder was investigated, firstly, by smoke visualization technique. Our attention was paid on the velocity profiles in the separated region on the cylinder where the secondary vortex is formed. It was found that Taneda's criterion must be carefully applied to the determination of the unsteady separation point from the integrated streak which was initially ejected from a nozzle.
Next, numerical calculations were performed by both direct calculation of Navier-Stokes'equations and a discrete vortex method. The tertiary vortex observed by the smoke visualization was also obtained by the numerical calculations; its generation could be reasonably explained from the velocity profiles.
