Turbulence spreading, anomalous transport, and pinch effect

A paradigmatic model describing transport and turbulence spreading as coupled processes is proposed, trying to unify the approaches of penetrative overshoot and overshoot. As a natural consequence asymmetric radial spreading of the turbulence, up-gradient transport of the particle density, and front propagation are observed. The model accounts for the interaction between the microscale of the turbulence and the meso-, respectively, system scale on which profile modifications occur. Comparison with direct numerical simulations of two-dimensional interchange turbulence shows qualitatively good agreement with the proposed transport model. Key transport features are reproduced even in the presence of coherent bloblike structures. Features of density pulse dynamics are also investigated. (c) 2005 American Institute of Physics.