A NUMERICAL STUDY OF INSTABILITIES IN CON FINED OPEN FLOWS

We present a general method of analysing instability dynamics. Numeric al simulations are performed with a code using a spectral finite eleme nt method for incompressible, unsteady flows. The presented systems ar e found to undergo a transition to an unstable state at a critical Rey nolds number. The method consists in extracting the perturbation field at various steps of the temporal development. The field in the linear regime gives the spatial eigenfunction and we observe its modificatio n due to non-linear behaviours. This distorsion is extracted to determ ine the parts of the flow field crucial for the non-linear dynamics.