Ken Bray

Partially premixed flamelets in LES of nonpremixed turbulent combustion

Partially premixed flames are observed in nonpremixed turbulent combustion when fuel and oxidizer have mixed before burning. This combustion regime combines the properties of both premixed and diffusion flames. A procedure based on the resolved fields is proposed to associate premixed and diffusion flame descriptions in large eddy simulation. Using basic and well known subgrid modelling of premixed and diffusion flames, the proposed methodology is tested for flames lifted in a two-dimensional turbulent wake. Very recent experimental observations concerning the dynamics of the flow field at the turbulent flame base are reproduced.

On the Regimes of Auto-Ignition in a Turbulent Medium

The process of auto-ignition in a non-premixed, homogeneous and isotropic turbulent medium is considered. The governing pdf transport equation is simulated via a Monte Carlo method. It is found that the pdf evolution depends on the relative magnitudes of two time scales, namely, that of turbulent mixing and of chemical reaction. Calculations made for a wide range of these time scales show that at least four different regimes of auto-ignition may be identified. These are classified into premixed and non-premixed type, and are located on a Damkohler number diagram.

Laminar Flamelets in Turbulent Combustion Modeling

ABSTRACT A brief review is presented of so-called laminar flamelet models of turbulent combustion processes, using premixed combustion as an example. Circumstances where this simple modeling strategy can fail are explored.