# Séminaire de Mécanique d'Orsay

## Le Jeudi 7 décembre 2017 à 14h00 - Salle de conférences du LIMSI

### Optimal mixing in stratified plane Poiseuille flow

## Florence Marcotte

DAMTP et BP Institute, Institut Jean le Rond d'Alembert

Mixing is an ubiquitous process in environmental flows. In
order to better understand the mechanisms involved in achieving
well-mixedness of a stratified flow, we investigate the optimisation
of mixing in stratified, 2D Poiseuille flow by means of a fully
nonlinear direct-adjoint looping method, where the initial
perturbation leading to maximal mixing efficiency over a given time
horizon is determined. A recent study by Foures et al. (2014) has
demonstrated that the widely-used approach consisting in maximizing
the time-averaged kinetic energy surprisingly results in largely
sub-optimal suppression of a passive scalar variance. By identifying
the initial perturbations which either maximize the kinetic energy
transient growth or minimize a specific `mix-norm' at a chosen target
time, we extend these results to the case of an active scalar. We show
how buoyancy modifies the optimal-mixing strategy and, by considering
the time evolution of the kinetic energy and potential energy
reservoirs, discuss the physical mechanisms involved in achieving
efficient irreversible mixing.

Accès Salle de conférences du LIMSI