SR13  Mecânica dos Fluidos    Titulo: LAMINAR-TURBULENT TRANSITION: A THEORETICAL MODEL OF THE NONLINEAR EVOLUTION OF THREE DIMENSIONAL WAVETRAINS IN BOUNDARY LAYERS   Resumo : SUMMARY. A WEAKLY NONLINEAR MODEL OF THE EVOLUTION OF THREE-DIMENSIONAL WAVETRAINS IN BOUNDARY LAYERS IS PRESENTED. THIS WAS MOTIVATED BY WIND-TUNNEL EXPERIMENTS WITH WAVETRAINS EMANATING FROM A POINT SOURCE. THE EXPERIMENTS SHOWED THAT THE FIRST SIGNATURE OF THE NONLINEARITY WAS THE APPEARANCE OF SECONDARY MEAN FLOW DISTORTIONS. THE DISTORTIONS WERE IN THE FORM OF LONGITUDINAL STREAKS WITH A SPANWISE STRUCTURE WHICH INCREASED IN COMPLEXITY WITH DOWNSTREAM EVOLUTION. THE MODEL LINKED THE STREAKS WITH A PAIRS OF COUNTER-ROTATING LONGITUDINAL VORTICES THAT DISTORT THE BASE MEAN FLOW BY A LIFT UP MECHANISM OF REDISTRIBUTION OF STREAMWISE MOMENTUM. THE MORE COMPLICATED STRUCTURES DEVELOPED FURTHER DOWNSTREAM ARE ALSO ADDRESSED. THEY ARE EXPLAINED BY A SECOND ORDER CORRECTION TO THE WEAKLY NONLINEAR MODEL. THE RESULTS SHOW QUALITATIVE AGREEMENT WITH THE EXPERIMENTAL OBSERVATIONS. KEY-WORDS: HYDRODYNAMIC INSTABILITY, LAMINAR-TURBULENT TRANSITION, BOUNDARY LAYERS, WEAKLY NONLINEAR THEORY, PERTURBATION METHODS.     Autores : Faraco de Medeiros, Marcello Augusto     Trabalho Completo :   COBEM99 | Comissão  Organizadora | Palestras | Sessões Técnicas | Autor | Simpósios e Sessões Especiais | Revisores |  Título  dos  Trabalhos | Local