Theoretical aspects of transition and turbulence in boundary layers
The main points of recent theoretical and computational studies on boundary-layer transition and turbulence are highlighted. The work is based on high Reynolds numbers and attention is drawn to nonlinear interactions, breakdowns, and scales. The article focuses in particular on truly nonlinear theories for which the mean-flow profile is completely altered from its original state. There appear to be three such theories, dealing with 1) nonlinear pressure-displacement interactions, 2) vortex/wave interactions, and 3) Euler-scale flows. Specific recent findings noted for these three, and in quantitative agreement with experiments, are the following. 1) Nonlinear finite-time breakups occur in unsteady interactive boundary layers, leading to sublayer eruption and vortex formation; here the theory agrees with experiments on the occurrence of the first spike. 2) Vortex/wave interactions give rise to finite-distance blowup of displacement thickness, then interaction and breakup (as “in 1”); this theory agrees with experiments on the formation of three-dimensional streets. 3) The Euler-scale and related theories lead to the prediction of turbulent boundary-layer microscale, displacement- and stress-sublayer thicknesses. © 1993 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.