Dr. Jacqueline H. Chen, Sandia National Laboratories, Livermore, CA

Abstract

Direct numerical simulation is used to investigate the effects of

unsteady stretch on turbulent flame propagation in premixed hydrogen/air

and methane/airflames. Thermo-diffusively unstable, neutral, and stable

hydrogen/air premixtures and stable methane/air premixtures are subjected

to unsteady strain and curvature effects imposed by 'two-dimensional'

isotropic turbulence. The ratio of the unsteady hydrodynamic to flame

time scales is varied by changing the initial turbulence intensity and

integral length scale. Flame propagation and stretch statistics along

with the Markstein number, based on consumption and displacement speeds,

are computed from the DNS data and compared with recent results from

unsteady counter-flow computations, experiment, and theory. For large

turbulence intensity, the unsteady strain time scale becomes less than

the flame transit time, and the premixed flame becomes less responsive

to unsteady strain. This results in significant reductions in the

Markstein number, consistent with results from linearized theory.
 
 

Jacqueline H. Chen, Sandia National Laboratories, Livermore, CA 94551-0969 Telephone: (510) 294-2586 Facsimile: (510) 294-1004

E-mail: jhchen@sandia.gov

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