Assessing Model Assumptions for Turbulent Premixed Combustion at High Karlovitz Number
Final rept. 1 Jun 2012-31 May 2015
CALIFORNIA INST OF TECH PASADENA
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Premixed turbulent flames in the high-Karlovitz regime are characterized and modeled using Direct Numerical Simulations DNS with detailed chemistry. To enable the present numerical study, a new time-integration scheme has been proposed for the simulation of stiff reacting flows. Using this scheme, a series of direct numerical simulations of high Karlovitz number, n-C7H16, turbulent premixed flames have been performed. It was found that the flame structure of these turbulent flames can be well captured by one-dimensional flames accounting for the effective species Lewis numbers. The reaction zone was found to remain thin, yet large fluctuations in the fuel burning rate were identified. Extinctions were observed only in the presence of differential diffusion, and these events were correlated with high curvature regions. A model to capture the burning fluctuations was proposed using a new flamelet approach. For the first time, the evolution of the turbulence both turbulent kinetic energy and enstrophy has been characterized through the flame. Under sufficiently high Karlovitz number, the first Kolmogorovs hypothesis has been confirmed. Finally, the impact of various chemicaltransport model assumptions on the evolution of turbulent flow field.
- Operations Research
- Fluid Mechanics
- Combustion and Ignition