Drag reduction in turbulent channel flow laden with finite-size oblate spheroids

M. Niazi Ardekani, P. Costa, W. -P. Breugem, F. Picano, L. Brandt

Published 2016-07-03Version 1

We study suspensions of oblate rigid particles in a viscous fluid for different values of the particle volume fractions. Direct numerical simulations have been performed using a direct-forcing immersed boundary method to account for the dispersed phase, combined with a soft-sphere collision model and lubrication corrections for short-range particle-particle and particle-wall interactions. We show that the drag is reduced and the turbulent fluctuations attenuated in flows laden with oblate spheroids not only when compared to suspensions of perfect spheres but also to the single phase turbulent flow. In particular, the turbulence activity decreases to lower values than those obtained by only accounting for the effective suspension viscosity. To explain the observed drag reduction we consider the particle dynamics and the interactions of the particles with the turbulent velocity field. We report the lack of the particle layer at the wall observed for spherical particles, which was found to be responsible for increased dissipation in these flows. Moreover, oblate particles near the wall rotate significantly slower and tend to stay with their major axes parallel to the wall. These effects lead to a decrease of the Reynolds stresses and turbulence production and so to the overall drag reduction in the turbulent channel flow of finite-size oblate spheroids.