  An initial-value problem for arbitrary small 3D vorticity perturbations
imposed on a free shear flow is considered. The viscous perturbation equations
are then combined in terms of the vorticity and velocity, and are solved by
means of a combined Laplace-Fourier transform in the plane normal to the basic
flow. This treatment allows for a simplification of the governing equations
such that it is possible to observe long transients, that can last hundreds
time scales. This result would not be possible over an acceptable lapse of time
by carrying out a direct numerical integration of the linearized Navier-Stokes
equations. The exploration is done with respect to physical inputs as the angle
of obliquity, the symmetry of the perturbation and the streamwise damping rate.
The base flow is an intermediate section of the growing 2D circular cylinder
wake where the entrainment process is still active. Two Reynolds numbers of the
order of the critical value for the onset of the first instability are
considered. The early transient evolution offers very different scenarios for
which we present a summary for particular cases. For example, for amplified
perturbations, we have observed two kinds of transients, namely (1) a monotone
amplification and (2) a sequence of growth - decrease - final growth. In the
latter case, if the initial condition is an asymmetric oblique or longitudinal
perturbation, the transient clearly shows an initial oscillatory time scale.
Furthermore, the more a perturbation is longitudinally confined the more it is
amplified in time. The long-term behavior of two-dimensional disturbances shows
excellent agreement with a recent two-dimensional spatio-temporal multiscale
modal analysis and with laboratory data concerning the frequency and wave
length of the parallel vortex shedding in the cylinder wake.
