Hierarchy of structure functions for passive scalars advected by turbulent flows

Lower bounds on the mix norm of passive scalars advected by incompressible enstrophy-constrained flows

Consider a diffusion-free passive scalar θ being mixed by an incompressible flow u on the torus Td. Our aim is to study how well this scalar can be mixed under an enstrophy constraint on the advecting velocity field. Our main result shows that the mix-norm (‖θ(t)‖H−1 ) is bounded below by an exponential function of time. The exponential decay rate we obtain is not universal and depends on the s...

The Fokker–Planck closure for turbulent molecular mixing: Passive scalars

Transport of Passive Scalars in Turbulent Channel Flow

A direct numerical simulation of a turbulent channel flow with three passive scalars at different molecular Prandtl numbers is performed. Computed statistics including the turbulent Prandtl numbers are compared with existing experimental data. The computed fields are also examined to investigate the spatial structure of the scalar fields. The scalar fields are highly correlated with the streamw...

Nonlocal transport of passive scalars in turbulent penetrative convection

We present a Green's function approach for quantifying the transport of a passive scalar (tracer) field in three-dimensional simulations of turbulent convection. Nonlocal, nondiffusive behavior is described by a transilient matrix (the discretized Green's function), whose elements contain the fractional tracer concentrations moving from one subvolume to another as a function of time. The approa...

Lagrangian views on turbulent mixing of passive scalars.

The Lagrangian view of passive scalar turbulence has recently produced interesting results and interpretations. Innovations in theory, experiments, simulations and data analysis of Lagrangian turbulence are reviewed here in brief. Part of the review is closely related to the so-called Kraichnan model for the advection of the passive scalar in synthetic turbulence. Possible implications for a be...