Mihkel Kree

Institute of Cybernetics

Using a technique allowing for in situ measurements of concentrations fields, the evolution of scalar mixtures flowing within a porous medium made of a three-dimensional random stack of solid spheres, is addressed. Two distinct fluorescent dyes are injected from separate sources. Their evolution as they disperse and mix through the medium is direct...

Majority of theoretical results regarding turbulent mixing are based on the model of ideal flows with zero correlation time. We discuss the reasons why such results may fail for real flows and develop a scheme which makes it possible to match real flows to ideal flows. In particular we introduce the concept of mixing dimension of flows which can ta...

Based on ray tracing approach, light propagation in inhomogeneous media with fluctuating coefficient of refraction n = n(r) can be interpreted as a chaotic mixing of the wavefront in the 6-dimensional phase space where the spatial coordinates are complemented by the respective wave vector components. According to ray tracing, the evolution of wave...

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A scalar field injected from a point source in a turbulent flow resolves into a set of elongated sheet-like structures whose concentration probability distribution P(C) is well understood in terms of the interplay between stretching histories of fluid particles, and molecular diffusion. Additionally, neighboring sheets may diffusively merge and evo...

The spectral signature of a turbulent scalar mixture is usually interpreted in terms of cascades, leading to decaying power laws either in the inertial range (the -5/3 slope), or in the viscous subrange (the -1 slope). An intermittent scalar field produced by an elongational velocity field, whatever it may be, also gives rise to a -1 power law. We...