Investigation of particle clustering in turbulent channel flow using Direct Numerical Simulations (DNS)

Particle-laden turbulent flows are prevalent in natural and industrial processes such as sedimentation in rivers, chemical reactors, pneumatic conveying of solids and gas scrubbers. Coupling between the particle and fluid phases as well as particle collisions can lead to flow modification. Hence, local particle concentration plays a vital role in the study of multiphase flow. Phenomenon like turbophoresis and particle clustering leads to formation of zones of high particle concentration. Particle response to fluid flow leads to the non-uniform spatial distribution of particles and depends on particle inertia, the ratio of particle size to the underlying fluid scales, etc. Many studies have been carried out to find the relevance of Stokes number on particle clustering. The present study is focused on the dependency of particle clustering on the Stokes number as well as the Reynolds number and mass loading, which are yet to be explored in detail. Direct Numerical Simulations (DNS) are carried out for vertical channel flow at different Reynolds numbers, Stokes numbers, and particle volume fractions. Particle clusters in the flow are identified by using the Voronoi tessellation method at different wall-normal locations. It is observed that clusters with larger areas are found at the channel center. Higher local particle concentration within the cluster is observed at high particle loading for both near-wall and channel center planes. PDFs of non-dimensionalized cluster area and particle concentration are used to reach a better understanding of cluster formation in the flow.