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Article

Turbulent channel flow of a dense binary mixture of rigid particles

Authors: Lashgari, I., Picano, F., Costa, , van Breugem, W. P., Brandt, L.B.
Document Type: Article
Pubstate: Accepted
Journal: Journal of Fluid Mechancis
Volume:   
Year: 2017

Abstract

We study turbulent channel flow of a binary mixture of finite-size neutrally-buoyant rigid particles by means of interface-resolved direct numerical simulations. We fix the bulk Reynolds number and total solid volume fraction, Reb = 5600 and \Phi= 20%, and vary the relative fraction of small and large particles. The binary mixture consists of particles of two different sizes, 2h/dl = 20 and 2h/ds = 30 where h is the half channel height and dl and ds the diameter of the large and small particles. While the particulate flow statistics exhibit a significant alteration of the mean velocity profile and turbulent fluctuations with respect to the unladen flow, the differences between the mono-disperse and bi-disperse cases are small. However, we observe a clear segregation of small particles at the wall in binary mixtures, which affects the dynamics of the near wall region and thus the overall drag. This results in a higher drag in suspensions with a larger amount of large particles. As regards bi-disperse effects on the particle dynamics, a non-monotonic variation of the particle dispersion in the spanwise (homogeneous) direction is observed when increasing the percentage of small/large particles. Finally, we note that particles of the same size tend to cluster more at contact whereas the dynamics of the large particles gives highest collision kernels due to a higher approaching speed.