Unsteady behavior of three-dimensional vortices relevant to turbulent boundary layers

The recent accomplishments are reviewed for a research program employing combined analytical-experimental techniques to study the three dimensional characteristics and behavior of vortex motions associated with the turbulence production process in turbulent boundary layers. Progress is described in the development of a new image processing technique which allows the derivation of quantitative data from flow visualization images. The method is used to search for the role of hairpin vortices in the turbulence production process. In the analytical portion of the study, calculations have been carried out to compute the evolution of a hairpin vortex in a shear flow; the interaction of a pair of hairpins has been examined as well as the viscous response at a wall due to the motion of a hairpin vortex. Comparison of these computer simulations with the experimental studies is very encouraging. Computations for the evolving flow between wall layer streaks during a typical cycle in the wall layer of a turbulent boundary layer have also been carried out; these studies show two possible routes to breakdown of the wall layer flow leading to the production process.