# Andrew D Bragg : Lagrangian irreversibility and inversions in 3 and 2 dimensional turbulence

Studying how small inertial particles suspended in turbulent flows
move relative to each other provides fundamental insights into their
transport, mixing and collisions. These insights are crucial for
tackling diverse problems ranging from droplet growth in warm clouds,
to planetesimal formation through collisional aggregation in turbulent
protoplanetary nebula. A deeper understanding of the relative motion
of the particles can be obtained by investigating both their
forward-in-time (FIT) and backward-in-time (BIT) dispersion. When FIT
and BIT dispersion are different it signifies irreversibility, and
since FIT and BIT dispersion are related to different problems,
understanding the irreversibility is of fundamental and practical
importance.

I will present new theoretical arguments and asymptotic predictions,
along with results from Direct Numerical Simulations (DNS) of the
governing equations, to show that inertial particle dispersion can be
very strongly irreversible in turbulence, with BIT being much faster
than FIT dispersion in 3-dimensional turbulence. The results also show
that inertial particles can disperse much faster than fluid
(interialess) particles. I will also present arguments, confirmed by
DNS results, that in 2-dimensional turbulence the nature of the
irreversibility and the direction of the particle energy fluxes can
invert when the particle inertia exceeds a certain threshold. These
results significantly advance our understanding of dispersion
problems, and lead to new capabilities for predicting the effect of
inertia on the rate at which particles spread out and mix together in
turbulence, and the rate at which they collide.

**Category**: Nonlinear and Complex Systems**Duration**: 01:39:37**Date**: November 14, 2017 at 2:55 PM**Views**: 153-
**Tags:**seminar, CNCS Seminar

## 0 Comments