Three-dimensional Voronoi analysis of preferential concentration of spheroidal particles in wall turbulence

Three-dimensional Voronoi analysis is performed to quantify both global and local aspects of clustering of inertial spheroidal particles in wall turbulence using data sets from a direct numerical simulation coupled with a Lagrangian point-particle approach. We consider oblate and prolate spheroids and characterize their inertia and shape by means of the Stokes number St and aspect ratio A, respectively. It is observed that particles tend to drift toward the wall, and this tendency is most prominent for St = 30. Although inertia dominates over shape on the particle clustering, intermediate asphericity (lambda = 0.33 and 3) is found to promote spheroids' flux to the wall for St <= 30, while heavy spheroids (St = 100) with greater departure from spheres (lambda = 0.1 and 10) distribute more evenly across the channel. The tendency of inertial spheroids to concentrate locally in preferred turbulence structures decreases with the distance from the walls. Owing to the particles' preferential distribution in lower-than-mean fluid velocity regions, the local clustering of spheroidal particles decreases with the increasing asphericity. Particles with large inertia (St >= 30), especially spheres and prolate spheroids, are more likely to cluster in the viscous sublayer. Published by AIP Publishing.