Séminaire exceptionnel – 9 juil. 2018 – 11h salle 250

Orientation patterns of non-spherical particles in turbulence

Bernhard Mehlig – öteborgs Univ., Suède

When non-spherical particles in a turbulent flow spend a long time near each other, they might reasonably be expected to converge toward the same orientation because turbulent strains tend to align the particles. We show here that this intuition fails in general: relative orientations of nearby particles are anomalously large because the distribution of relative orientations of nearby particles has heavy power-law tails. We measure the moments of this distribution in experiments and numerical simulations, and explain their anomalous scaling as a function of particle distance. Our analysis builds on a description of the relative motion in a phase space that includes not only the usual spatial coordinates, but also the angular degrees of freedom. In this phase space the dynamics evolves to a fractal attractor. Its fractal geometry depends on particle shape and determines the anomalous scaling exponents. Joint work with L. Zhao, K. Gustavsson, R. Ni, S. Kramel, G. Voth, and H. I. Andersson