Turbulence, Lagrangian Coherent Structures, and the Formation/Evolution of Life

Abstract:

Turbulent fluid flows have long been recognized as a superior means of diluting initial concentrations of scalars 
due to rapid stirring. Conversely, studies have shown that the structures responsible for this rapid dilution can 
also aggregate initially distant reactive scalars and thereby greatly enhance reaction rates.  In previous work, we 
demonstrated that Lagrangian coherent structures (LCS) are directly responsible for this coalescence of reactive 
scalar filaments. More recently, we have turned our attention to turbulent free-surface flows that transport buoyant 
particles. Due to their buoyancy, particles are exposed to a non-divergence-free velocity field, which leads to 
clustering and unmixing behavior, a reversal of the typical arrow of time in which turbulence acts to mix and 
dilute. Using both an experimental and numerical approach, we show that LCS are responsible for this unmixing and 
the formation of organized clusters. For initially distant, buoyant scalars on a turbulent free surface, LCS are 
responsible for both the coalescence and clustering of scalars which results in an increased likelihood of observing 
reaction enhancement. As a thought experiment, we discuss the implications of these results in terms of turbulent 
structure acting as a organizing template that facilitated the formation and subsequent evolution of life.