Abstract: Two-dimensional imcompressible viscous flows around a circular cylinder with periodic oncoming flow from infinity are investegated. By means of spectrum method, the stream functions are developed into Fourier series, so the stream functions depend on angle 0 continuousely. Numerical calculations are implemented for stream functions as well as vortices for the case K_c=4 and Re=200. The results manifeste that the method used here has the advantage of simplicity and saving computer time comparing with the method of fully discretiged N-S egs. and discretiged vortices method.

Key words: numerical method for N-S eqs., flow around a circular cylinder, periodic oncoming flow from infinity, spectrum method