Peter J. Ireland

Forward and backward in time dispersion of fluid and inertial particles in isotropic turbulence

In this paper, we investigate both theoretically and numerically the Forward-In-Time (FIT) and Backward-In-Time (BIT) dispersion of fluid and inertial particle-pairs in isotropic turbulence. Fluid particles are known to separate faster BIT than FIT in three-dimensional turbulence, and we find that inertial particles do the same. However, we find that the irreversibility in the inertial particle dispersion is in general much stronger than that for fluid particles. For example, the ratio of the BIT to FIT mean-square separation can be up to an order of magnitude larger for the inertial particles than for the fluid particles. We also find that for both the inertial and fluid particles, the irreversibility becomes stronger as the scale of their separation decreases. Regarding the physical mechanism for the irreversibility, we argue that whereas the irreversibility of fluid particle-pair dispersion can be understood in terms of a directional bias arising from the energy transfer process in turbulence, inertial...

Improving particle drag predictions in Euler–Lagrange simulations with two-way coupling

Euler–Lagrange methods are popular approaches for simulating particle-laden flows. While such approaches have been rigorously verified in the dilute limit (where particles do not noticeably alter their carrier flow), much less verification has been attempted for cases where the coupling between the two phases leads to non-negligible modifications in the local fluid velocity. We review one of these techniques for coupled fluid–particle flows, the volume-filtered Euler–Lagrange method, and show that it (like many similar methods) provides erroneous predictions for the interphase drag force due to the presence of the particles. We show that these errors are tied to inaccuracies in the numerical implementation of the drag model for systems with two-way coupling. We therefore introduce a simple approach to correct the implementation of this drag model, and show that this corrected implementation provides accurate and grid-independent predictions of particle settling in two-way coupled flows at low particle Reynolds numbers. Finally, we study the effect of the corrected implementation on a more complicated, cluster-induced turbulence flow.