SPATIAL CHAOS IN BOUNDARY-LAYER-TRANSITION

Experiments have been performed on a laminar flat plate boundary layer undergoing transition to turbulence. Reproducible disturbances were i ntroduced via a loudspeaker embedded at some upstream location and the ir evolution over the plate measured using hot-wire anemometry. A new technique has been used to estimate the number of nonlinearly independ ent modes in the reconstructed phase portraits. Nonlinear maps were th en fitted that explicitly model the spatial evolution of disturbances. These maps are consistent with classical linear stability theory for small disturbances, and give rise to 'Smale horse-shoe' like behaviour for larger amplitude disturbances. Thus a mechanism for generating ch aos has been uncovered.