K-SPECTRUM OF PASSIVE SCALARS IN LAGRANGIAN CHAOTIC FLUID-FLOWS

An eikonal-type description for the evolution of k spectra of passive scalars convected in a Lagrangian chaotic fluid flow is shown to accur ately reproduce results from orders of magnitude more time consuming c omputations based on the full passive scalar partial differential equa tion. Furthermore, the validity of the reduced description, combined w ith concepts from chaotic dynamics, allows new theoretical results on passive scalar k spectra to be obtained. Illustrative applications are presented to long-time passive scalar decay, and to Batchelor's law k spectrum and its diffusive cutoff.