Lagrangian analysis of enstrophy dynamics in a highly turbulent premixed flame

Abstract

A Lagrangian analysis approach is used to examine the effects of heat release on the dynamics of the enstrophy during highly turbulentpremixed combustion. The analysis is performed using data from a direct numerical simulation of a statistically planar premixed methane–air flame at a Karlovitz number of 100. Through cumulative, conditional, and correlation analyses, we show, consistent with prior studies, that vortex stretching and baroclinic torque both increase enstrophy at these highly turbulent conditions, while viscous transport and dilatation both lead to enstrophy destruction. However, although vortex stretching and viscous transport are individually an order of magnitude greater than all other terms in the enstrophy budget, the cumulative and combined effect of these two terms along Lagrangian trajectories is roughly only twice as large as the combined cumulative effect of dilatation and baroclinic torque. Moreover, trajectories that exhibit an increase in enstrophy through the flame are found to frequently have cumulative contributions from budget terms outside a single standard deviation of the mean contribution, indicating that enstrophy production at such highly turbulent conditions is associated with relatively infrequent but large values of dynamical terms. Lagged correlations further reveal a small but measurable contribution of baroclinic torque in enstrophy production, but these increases are overwhelmed, on average, by concurrent decreases in enstrophy due to viscous transport and dilatation. Taken together, these results provide further understanding of enstrophy dynamics in highly turbulent premixed flames.

Publication
Physics of Fluids
Ryan Darragh
Ryan Darragh
Computational Physicist
Colin Towery
Colin Towery
Postdoctoral Research Associate

Colin is a former research associate in the Paul M. Rady Department of Mechanical Engineering at the University of Colorado Boulder and also a former student in the Turbulence and Energy Systems Laboratory, earned his PhD in May 2018.

Michael Meehan
Michael Meehan
PhD Student

Mike is a graduate student using computation fluid dynamics to understand fundamental physics in turbulent combustion problems.

Peter Hamlington
Peter Hamlington
Associate Professor

Peter is an associate professor in the Paul M. Rady Department of Mechanical Engineering at the University of Colorado Boulder and the principal investigator of the Turbulence and Energy Systems Laboratory.