Table of Contents Author Guidelines Submit a Manuscript
Modelling and Simulation in Engineering
Volume 2012, Article ID 619419, 22 pages
http://dx.doi.org/10.1155/2012/619419
Research Article

New Theories on Boundary Layer Transition and Turbulence Formation

Department of Mathematics, The University of Texas at Arlington, Arlington, TX 76019, USA

Received 26 January 2012; Accepted 25 March 2012

Academic Editor: Guan Heng Yeoh

Copyright © 2012 Chaoqun Liu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This paper is a short review of our recent DNS work on physics of late boundary layer transition and turbulence. Based on our DNS observation, we propose a new theory on boundary layer transition, which has five steps, that is, receptivity, linear instability, large vortex structure formation, small length scale generation, loss of symmetry and randomization to turbulence. For turbulence generation and sustenance, the classical theory, described with Richardson's energy cascade and Kolmogorov length scale, is not observed by our DNS. We proposed a new theory on turbulence generation that all small length scales are generated by “shear layer instability” through multiple level ejections and sweeps and consequent multiple level positive and negative spikes, but not by “vortex breakdown.” We believe “shear layer instability” is the “mother of turbulence.” The energy transferring from large vortices to small vortices is carried out by multiple level sweeps, but does not follow Kolmogorov's theory that large vortices pass energy to small ones through vortex stretch and breakdown. The loss of symmetry starts from the second level ring cycle in the middle of the flow field and spreads to the bottom of the boundary layer and then the whole flow field.