Preferential Concentration of Particles in Forced Turbulent Flows: Effects of Gravity

The impact of gravity on the particle preferential concentration is investigated by direct numerical simulations in an Eulerian-Lagrangian framework for a large range of Stokes numbers St(n) = 0.01 similar to 4. For particles with small Stokes numbers such as St(n) = 0.01, the gravity has minor effects on the particle spatial distribution in the turbulence. With increasing St(n), stripped structures of the high number density of particles appear and expand along the gravity direction. Different evaluation methods of particle preferential concentration are discussed such as the spatial distribution, the box index, and the probability density function. The number density of particles in the accumulating regions reduced under the influence of gravity. The reduction becomes prominent for the particle cloud at Stokes number St(n) approximate to 1, especially in the clusters of high particle number density. For large Stokes number St(?), the slip velocity significantly increases due to the particle gravity. Due to the gravity, the particle concentration reduces globally, particularly in the low vorticity regions. For the Stokes number range explored in this paper, gravity has a considerable impact on the particle-turbulence interaction.

Automated summary

The impact of gravity on particle preferential concentration is studied using direct numerical simulations in an Eulerian-Lagrangian framework for a wide range of Stokes numbers St(n) from 0.01 to 4. Gravity has a minor effect on the spatial distribution of particles in turbulence for small Stokes numbers like St(n) = 0.01. However, as St(n) increases, stripped structures of high particle density appear and expand along the gravity direction.