ON THE ENVIRONMENTAL REALIZABILITY OF ALGEBRAICALLY GROWING DISTURBANCES AND THEIR RELATION TO KLEBANOFF MODES

A theoretical explanation of some experimentally observed phenomena as sociated with the so-called Klebanoff modes is obtained by analyzing t he flow over a finite thickness flat plate resulting from a small-ampl itude distortion imposed on the upstream mean flow. The analysis shows (among other things) how the stretching of the vortex lines around th e plate leads to streamwise vorticity at the plate surface, which then produces a streamwise velocity perturbation within the boundary layer that can be related to the experimentally observed Klebanoff mode. Th e complete evolution of this flow must be found by solving the boundar y-region equations of Kemp (1951) and Davis and Rubin (1980), but a li miting analytical solution can also be obtained. Since the initial gro wth of the boundary-layer disturbance is nearly algebraic, our results demonstrate how the algebraically growing disturbances promoted by La ndahl and others can be generated by a realistic external-disturbance environment. The relationship between these results and various bypass transition mechanisms is discussed.