Lagrangian Coherent Structures: A Template for the Prediction of Reaction 
Zones in Turbulent Flows.

Abstract:

Turbulent fluid flows have long been recognized as a superior means of quickly 
diluting concentrated scalars due to chaotic stirring. The structures 
contained within turbulent flows that are responsible for this rapid dilution, 
however, have been experimentally shown to aggregate initially distant 
reactive scalars and greatly enhance reaction rates. Through the use of 
chaotic dynamics and the calculation of finite time Lyapunov exponents, we 
have utilized numerical models to demonstrate that Lagrangian coherent 
structures are directly responsible for the coalescence of reactive scalar 
filaments. This coalescence of highly concentrated filaments can then lead to 
reaction rates orders of magnitude greater than is predicted by a well mixed 
system. Reaction enhancement can be beneficial when the goal is to maximize 
reaction products, such as for coral broadcast spawning along coastal reefs 
where fertilization between distant egg and sperm is necessary, or 
detrimental, i.e. the aggregation of hazardous oil spills and bio-diverse 
phytoplankton blooms in the open ocean.  Fluid turbulence, therefore, should 
be renowned not only for its ability to dilute, but also its tendency to 
organize initially distant scalars along the same attracting regions in the 
flow.