Direct Numerical Simulation of Flame Annihilation in Turbulent Premixed Combustion
Michael Walker, Princeton University
Full-fidelity simulations of turbulent fluid flows require the spatial and temporal scales of turbulent structures to be fully resolved. Furthermore, turbulent combustion, a chemically reacting flow, requires solving a transport equation for each chemical species within a complex reaction mechanism and the resolution of said spatial and temporal scales. For practical engineering simulations, reduction of this large, coupled system of partial differential equations is a computational necessity. In premixed combustion, reduced-order manifold models project the thermochemical state onto a one-dimensional space in progress variable, from unburned reactants to burned products at thermodynamic equilibrium. Under conditions where turbulence intensity is high and the length scales of turbulence are small (comparable to the reaction zone thickness), the curvature of the reaction zone increases until the reaction zone structure is so corrugated that it may interact with itself. These reaction zone-reaction zone interactions are important in the structure of flame propagation (creating, in effect, a highly broadened flame brush) and as a principal mechanism of local extinction and continuous annihilation of turbulent flame surfaces. Whether these interactions can be captured by the manifold model remains an open question. This work explores the influence of reaction zone-reaction zone interactions on the local thermochemical state using Direct Numerical Simulation of planar turbulent flames. In future work, additional simulations of spherical turbulent flames (with high mean curvature) will also be conducted. These database will be compared to predictions from the manifold model to understand what additional physics may need to be included to capture reaction zone-reaction zone interactions.