Decomposition of mixing layer turbulence into coherent structures and background fluctuations

The eduction of coherent structures from cross-wire rake data in a fully tu rbulent incompressible mixing layer confirms the feasibility of a decomposi tion of a turbulent flow field, first suggested by Farge, as non-periodic n on-equilibrium coherent structures interacting with a 'thermalized' broad-b and turbulence. A simple wavelet coefficient decimation algorithm and ortho gonalization yields non-periodic dominant flow structures and a background field that has a Gaussian distribution of velocities at the centerline. The coherent structures are classified in terms of their topology. The non-coh erent background field has flat energy spectra and normal distribution of v elocity components. Most background held statistics depend only weakly on t he type of structure on which they are superposed. It may be possible to ad apt existing subgrid scale models to this decomposition.