Scaling and collapse of conditional velocity structure functions in turbulent premixed flames

Abstract

A new scale-sensitive physical-space conditional analysis is outlined and used to examine the scaling and collapse of velocity structure functions in turbulent premixed flames. The conditioning is based on local instantaneous temperatures in the premixed flame, and structure function scaling and collapse are examined using Kolmogorov-type dimensional arguments and scaling relations. Both longitudinal and lateral structure functions are computed using the local flame normal and tangent as reference directions. The analysis is based on data from direct numerical simulations of unconfined statistically-planar flames at three different intensities of turbulence in the premixed reactants. The analysis shows that as the turbulence intensity increases and for locations near the unburnt reactants, conditional structure functions approach the rN/3 inertial range scaling predicted by Kolmogorov, where N is the structure function order. Using conditionally-calculated scaling variables, it is further shown that structure functions throughout the flame increasingly collapse as the turbulence intensity increases, with a more complete collapse observed for longitudinal structure functions and for small r within the analytic (or dissipative) range. These results suggest that, at sufficiently high intensities, Kolmogorov-type scaling laws and dimensional arguments may retain some validity in premixed flames, provided that scaling variables are computed on a conditional basis for different temperatures.

Publication
Proceedings of the Combustion Institute
Sam Whitman
Sam Whitman
PhD student
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.

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.