Effects of Turbulent Advection on Thermochemical Trajectories in Premixed Flames

Abstract

A Lagrangian analysis approach is used to track changes in reactant mass fraction and temperature within fluid parcels during premixed combustion. Time series of the reactant mass fraction and temperature along fluid parcel trajectories, termed “thermochemical trajectories,” are calculated using data from direct numerical simulations of unconfined premixed flames for two different turbulence intensities. Both of the turbulence intensities are high, with Karlovtiz and Damköhler numbers corresponding a broadened flame. By analyzing time series of reactant mass fraction and temperature along fluid parcel trajectories, we show that fuel consumption and temperature rise within fluid parcels are frequently non-monotonic, resulting in frequent cooling events even after the temperature within a parcel has risen to 1400 K or more. Through an analysis of dynamical effects in the governing equation for the reactant mass fraction, this non-monotonicity is shown to be due to strong molecular diffusive processes resulting from the creation of large thermochemical gradients by turbulent advection. Implications of these results for the understanding of turbulent premixed flame dynamics and structure are outlined.

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.

Ryan Darragh
Ryan Darragh
Computational Physicist