  This paper serves as a review of our recent new DNS study on physics of late
boundary layer transition. This includes mechanism of the large coherent vortex
structure formation, small length scale generation and flow randomization. The
widely spread concept vortex breakdown to turbulence,which was considered as
the last stage of flow transition, is not observed and is found theoretically
incorrect. The classical theory on boundary layer transition is challenged and
we proposed a new theory with five steps, i.e. receptivity, linear instability,
large vortex formation, small length scale generation, loss of symmetry and
randomization to turbulence. We have also proposed a new theory about
turbulence generation. The new theory shows that all small length scales
(turbulence) are generated by shear layer instability which is produced by
large vortex structure with multiple level vortex rings, multiple level sweeps
and ejections, and multiple level negative and positive spikes near the laminar
sub-layers.Therefore, turbulence is not generated by vortex breakdown but
rather positive and negative spikes and consequent high shear layers. Shear
layer instability is considered as the mother of turbulence. This new theory
may give a universal mechanism for turbulence generation and sustenance which
shows that the energy is brought by large vortex structure through multiple
level sweeps.
