Temporal evolution of high-order vortices in the nonsymmetric wake past a circular cylinder

The nonsymmetric, nonsteady flow of a viscous incompressible fluid around an impulsively started circular cylinder at Reynolds number Re=3000 (based on the free stream velocity and cylinder diameter) is numerically simulated to explore the evolution in time of high-order vortices developing in the cylinder near wake. The two-dimensional Navier-Stokes equations in the streamfunction-vorticity transport form are numerically integrated with the use of a computational technique in which the flow fields are expanded in Fourier series along the azimuthal direction and the convolutions arising from the convective term of the vorticity transport equation are evaluated by means of fast Fourier transform algorithms; the time marching is executed with a fourth-order Runge-Kutta algorithm (first four iterations) and a predictor-corrector scheme for the subsequent iterations. The evolution in time of primary, secondary and tertiary vortices developing in the early stages of development of the nonsymmetric wake of the cylindrical body clearly emerges from the numerical simulations and is accurately described; the results are presented in terms of computer generated images of streamline fields and vorticity fields. The mutual interaction of vortical structures of different order in the near wake of the cylinder appears in the results of the calculations. (C) 2002 Published by The Japan Society of Fluid Mechanics and Elsevier Science B.V. All rights reserved.