Published online by Cambridge University Press: 26 April 2006
The influence of finite-amplitude perturbations on the unsteady vortex shedding past an impulsively started circular cylinder is investigated by means of a numerical model. The computational scheme is a mixed spectral–finite analytic technique, in which the fast-Fourier-transform algorithm is used for the evaluation of the nonlinear terms in the two-dimensional time-dependent Navier–Stokes equations in their stream function–vorticity transport form (the Helmholtz formulation) at Re = 1000. The vortex shedding is promoted by imposing at t = 0 a small rotational field to the initially irrotational flow. Attention is focused on the strength of the perturbation vortex, which affects the way in which the vortex shedding develops in time. The results of the simulations are presented by means of computer-generated drawings of absolute streamlines, relative streamlines and vorticity fields; it appears that, when the strength of the initial perturbation assumes the minimum value that has been tested, the vortex shedding phenomenon develops in a way different from that resulting from other numerical experiments of the same kind.