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Journal of Flow Visualization and Image Processing
SJR: 0.161 SNIP: 0.312 CiteScore™: 0.1

ISSN Imprimer: 1065-3090
ISSN En ligne: 1940-4336

Journal of Flow Visualization and Image Processing

DOI: 10.1615/JFlowVisImageProc.v12.i1.50
pages 45-72

UNSTEADY DEVELOPMENT OF VORTICAL STRUCTURES IN THE SYMMETRIC NEAR WAKE OF A CYLINDER

Giancarlo Alfonsi
Fluid Dynamics Laboratory, Universita della Calabria, Via P. Bucci 42b, 87036 Rende (Cosenza), Italy

RÉSUMÉ

The time-dependent Navier-Stokes equations in their streamfunction-vorticity transport form are numerically integrated to explore the early temporal stages of the evolution of vortical structures of different order in the near wake of a circular cylinder. The numerical technique used is a mixed spectral-finite analytic scheme in which the flow fields are expanded in Fourier series along the azimuthal direction and the convolutions arising from the convective terms of the vorticity transport equation are calculated by means of Fast Fourier Transform algorithms. The time advancement is performed by using a fourth-order Runge— Kutta algorithm (first four iterations) and a Predictor—Corrector scheme (subsequent iterations). The time-dependent case of a viscous incompressible fluid flowing around an impulsively started circular cylinder at the Reynolds number Re = 3000 (based on free-stream velocity and cylinder diameter) is considered, with particular attention to the evolution in time of primary, secondary, and tertiary vortices developing in the near wake of the cylinder numerically kept in its symmetric configuration. The results are presented for several time steps of integration mainly in terms of computer-generated images of streamlines and vorticity fields, describing the reciprocal interaction of vortical structures of different order in the near wake of the cylindrical body.


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