Fundamental studies on stratified mixing – STRATIMIX
Fluids with inhomogeneous temperature or chemical species concentrations are often encountered in geophysical and industrial flows. When those tracers modify the specific weight of the fluid, the setting of a stable density stratification is frequently observed. It is then natural to wonder how the turbulent mass transfers are affected by this stratification ? When a stratified fluid is mixed, some part of the kinetic energy injected in the system is transferred into potential energy, while the remaining part is dissipated. How can we estimate mixing efficiency, and how do mixing properties depend on the stratification, the forcing or the diffusivity of the active tracer ? The aim of this project is to improve our understanding of mixing in stratified fluids by designing innovative laboratory and numerical experiments. We will first realize a laboratory experiment where a stratified fluid is mixed in a closed system, and for which a complete energy budget will be achieved. A particular care will be given to the measure of stratification and to the estimate of the mechanical energy injected in the system. We will in a second stage use the most advanced visualization techniques (PLIF/PIV) in order to perform local measurements of mixing dynamics in the previous experimental set-up. These local measurements will allow to characterize statistical properties of turbulent mixing, like PDF of density fluctuations. We will finally consider the case of decaying stratified turbulence by studying the evolution of a stable density profile in a salt-stratified water tunnel. All these experimental results will be compared to existing models for the turbulent diffusivity in the presence of stratification. Notably, there are still strong discrepancies between these models, depending on the scientific community. We also propose to generalize to stratified fluids a self-convolution mixing model that was initially developed in the context of passive tracer advected by an homogeneous isotropic turbulent flow. High resolution Direct Numerical Simulations will be performed on a selection of laboratory experiments. These simulations, validated by comparison to the laboratory experiments, will provide additional data in a range of parameter not directly accessible to the experiments. The STRATIMIX project gathers young researchers of LFMA and ENS-Lyon. This is an indicator of the dynamism of its participants, and of the good integration of the project in the educative and scientific policy of the host laboratory.
Monsieur Louis GOSTIAUX (Laboratoire de Mécanique des Fluides et d'Accoustique) – email@example.com
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
LMFA Laboratoire de Mécanique des Fluides et d'Accoustique
Help of the ANR 180,000 euros
Beginning and duration of the scientific project: December 2013 - 42 Months