FRACTAL PROPERTIES OF MIXING BY CHAOTIC A DVECTION

Results concerning the fractal properties of isovalue surfaces of a pa ssive, diffusive scalar field being advected by a three-dimensional, s teady flow exhibiting chaotic streamlines are presented. We show that the mixing efficiency is related to the extent of the so-called ''adve ctive'' zone for which the similarity dimension is optimal for mixing (D-s = 3): the effective mixing time is related to the diffusive time of the cut-off scale which bounds this zone. For partial chaos, this c ut-off corresponds to the size of the regular region which limits asym ptocally the mixing.