Abstract
Quasi-periodic nature of large-scale motions in the outer region of turbulent boundary layer is considered. A simple model calculation using a 2D discrete vortex method is performed on the presumption that the mechanism responsible to the quasi-periodicity might be an inviscid, varicose-mode instability of a symmetrical vorticity field which consists of a boundary layer flow under consideration and its mirror image with respect to the wall. The preferred wavelength determined from the model flow is roughly comparable with but non-negligibly longer than the corresponding wavelength observed by Taneda(1982) in his flow visualization experiments.
