ASYMPTOTIC MODELING FOR SEPARATING BOUNDARY-LAYERS IN A CHANNEL

The purpose of this work is to give a formal asymptotic method to anal yse systematically the significant perturbations which deeply change t he nature of the flow of the wall boundary layer of a channel at high Reynolds numbers. The fluid is assumed Newtonian and the how laminar t wo-dimensional and steady. The theory developed here explains the sepa ration over significant wall disturbances. In particular, we show that the perturbation that induces the triple deck structure can both disp lace the classical boundary layer and cause separation of the Row. Bes ides there exist a series of disturbances, smaller but ''stronger'', t hat cause a separation of the boundary layer without displacing it. Th is series is limited by the smallest perturbation compatible with the hypothesis of the theory, thus leading to a theory in double deck.