By direct numerical simulation of Navier-Stokes equations the reconnection of two anti-parallel vortex tubes has been studied in terms of the pseudo-spectral method.The influence of different disturbances for initial vortex tubes on reconnection is observed. "Curved vortex belts" are found,and the physical mechanism for the amplification of background vorticity is also investigated.

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.