Multiscale interaction of inertial particles with turbulent motions in open channel flow

Abstract

Direct numerical simulations two-way coupled with inertial particles are used to investigate the particle distribution and two-way coupling mechanisms in turbulent open channel flow. In particular, the relationship between low- and high-inertia particles and the distinct large-scale motions (LSMs) and very-large-scale motions (VLSMs) which are characteristic of high-Reynolds-number, wall-bounded turbulence are examined. To do this, two methods of spatial filtering are applied to isolate the effects of LSMs versus VLSMs and separately analyze their interactions with inertial particles. One method of filtering the VLSMs from the flow is via artificial domain truncation, which alters the mean particle concentration profile and particle clustering due to the absence of VLSMs. The second method uses on-the-fly low- and high-pass filtering on the velocity field seen by the particles, so that as the simulation progresses the particles can only couple with certain scales of the flow. The results show that turbophoretic drift of particles toward the wall and the resulting increase in near-wall concentration is underpredicted without VLSMs, whereas the small-scale clustering and two-way coupling effects are mainly determined by particle coupling with LSMs. In the inner layer, the elongated streamwise anisotropic particle clustering can be reproduced by coupling solely with LSMs for low Stokes number. However, we do not observe a similar particle clustering behavior in the outer layer as seen in the full simulation by coupling particles with either LSMs or VLSMs at high Stokes numbers. This indicates that the organized particle structures are formed by the joint action of LSMs and VLSMs, especially for high-Stokes-number particles in the outer layer. The implications of these scale interactions are discussed in the context of large eddy simulation (LES) of one- and two-way coupled flows.