Statistics of velocity and preferential accumulation of micro-particles in boundary layer turbulence (original) (raw)

Particle drift in turbulent flows: the influence of local structure and inhomogeneity

The way particles interact with turbulent structures, particularly in regions of high vorticity and strain rate, has been investigated in simulations of homogeneous turbulence and in simple flows which have a periodic or persistent structure e.g. separating flows and mixing layers. The influence on both settling under gravity and diffusion has been reported and the divergence (compressibility) of the underlying particle velocity field along a particle trajectory has been recognized as an important quantity in quantifying these features. This paper shows how these features can be incorporated in a formal way into a two-fluid model of the dispersed particle phase. In particular the PDF equation for the particle velocity and position is formerly derived on the basis of a stochastic process that involves the statistics of both the particle velocity and local compressibility along particle trajectories. The PDF equation gives rise to contributions to both the drift and particle diffusion...

ON THE PREFERENTIAL CONCENTRATION OF INERTIAL PARTICLES DISPERSED IN A TURBULENT BOUNDARY LAYER

The distribution of inertial particles in turbulent flows is strongly non-homogeneous and is driven by the structure of the flow field. In this work, we examine the relationship between particle concentration and flow field in a turbulent channel (Reτ = 150). We use DNS combined with Lagrangian tracking of particles, with Stokes numbers equal to 0.2, 1, 5 and 25, to characterize the effect of inertia on particle preferential accumulation. Comparing the Eulerian statistics for fluid and particles, we observe differences which can be explained by the particle preferential sampling of the underlying carrier flow field. This turbulent preferential sampling appears responsible for particle accumulation in the boundary layer. To measure particle preferential accumulation we use the Jacobian, J(t), of the dispersed phase measured along a particle trajectory. This quantity measures the compression of an elemental volume of the dispersed phase along a particle trajectory and is related to th...