Dynamics of inertial particles in free jets

Abstract

Turbulent mixing of small and diluted inertial particles presents many peculiar and unexpected features such as preferential segregation at small scales, i.e. clustering or, in wall flows, preferential wall accumulation, i.e. turbophoresis, which are induced by the multi-scale features of the turbulence in the carrier fluid. In the context of multi-phase flows, the effect of turbulence on particle distributions was commonly addressed in simplified geometries as in homogeneous or channel flows. The present paper discusses the dynamics of suspensions with different inertia in the far field of turbulent axisymmetric jets by means of direct numerical simulations. The jet is a well-known constant Reynolds number flow where the characteristic length scale grows linearly with distance from the jet origin, while the characteristic velocity decays in inverse proportion. These features, combined with the finite inertia, induce peculiar non-equilibrium effects on the spatial distribution of the particles. They range from spatially developing small-scale clustering, due to the multi-scale nature of the turbulent fluctuations, to self-similarity of the mean particle velocity profile, presumably collapsing on a one-parameter family of shapes parameterized in terms of the local large-scale Stokes number. The properties presented here are the most evident features of this most interesting system, where intermittency and spatial inhomogeneity interact to induce even subtler effects of spatial segregation, which certainly deserve further investigation.