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Mirza F. Baig
School of Engineering The University of Warwick Coventry CV4 7AL, UK

Sergei I. Chernyshenko
Department of Aeronautics Imperial College London Prince Consort Rd., London SW7 2AZ


A direct numerical simulation of quasi-2D (that is with flow parameters independent of longitudinal coordinate) decaying and forced turbulence and 3D turbulence in channel flow was performed with the intention of ascertaining the sustenance mechanism of near-wall turbulence by investigating the mechanism of streak formation. We found the existence of streaks in quasi-2D flows thus demonstrating that contrary to many theories, feedback from longitudinal flow is not necessary for streak formation. Passive scalars having different mean scalar profiles were introduced in forced quasi-2D and 3D turbulent flows in order to compare the streak spacing of the scalars deduced from two-point correlations of DNS results with results obtained theoretically. It has been found that even for the same vortex structure for all the passive scalars there is a marked variation in streak spacing implying that the preferential streak spacing is not necessarily linked to the preferential vortex spacing. The obtained qualitative numerical results are in favour of the theory of streak formation based on optimal perturbation (Butler and Farrel 1993) but at the same time they clearly indicate that the good quantitative agreement reported for that theory may be fortuitous.