Regeneration mechanism of streaks in near-wall quasi-2D turbulence

A direct numerical simulation of quasi-2D (that is with flow variables independent of streamwise direction) decaying and forced turbulent flow in a channel was performed in order to seek out the sustenance mechanism of near-wall turbulence by uncovering the mechanism of streak formation. We found the existence of streaks in quasi-2D turbulent flows, thereby demonstrating that feedback from longitudinal flow is not necessary for streak formation. Passive scalars having different mean profiles were introduced in forced quasi-2D turbulent flows in order to compare the streak spacing of the scalars deduced from two-point correlations of DNS results with those obtained from optimal perturbation and Reynolds normal stress anisotropy instability mechanisms. It has been found that although for all the passive scalars the vortex structure is the same, there is a marked variation in streak spacing of the scalars implying that the preferential streak spacing is not necessarily linked to the preferential vortex spacing