Computational investigation of thermo-diffusive instabilities in flames: from laminar cellular structures to turbulent flows

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The propagation of unstable flames is at the center of numerous natural phenomena and engineering applications. Understanding and modeling these unstable flames and how they interact with turbulent flows are of critical importance to designing efficient and clean energy conversion devices, mitigating the risks of accidental explosions, and understanding astrophysical phenomena. This work is to conduct a computational study to reveal a complete picture of the geometry of the near-limit premixed flame front. While the primary focus is on thermo-diffusively unstable flames, the results are expected to shed light onto numerous additional scientific problems. This work will lead to the development of high-fidelity computational models, which will be used for designing and optimizing high-performance combustion systems for propulsion application.Experimental observations and theoretical studies have long pointed out the differences between laminar stable flames and thermo-diffusively unstable flames. Unfortunately, state-of-the-art techniques currently used to simulate large-scale turbulent flames fail to adequately predict the flow field of reacting mixtures that are intrinsically unstable. This work is to quantify the fundamental characteristics that make unstable flames different from their stable counterparts: the size of the cellular structure and the acceleration of the flame front propagation. These two features form the foundation onto which any Large Eddy Simulation (LES) models will be built: they determine the size of the LES filter and control the closure of the chemical source terms. The strength of the proposal relies on considering an extensive range of conditions from 1D spherical flames, to 2D stationary tubular flames, to 3D unstable laminar and turbulent flames. Throughout the analysis, no shortcut of accuracy will be taken, and previously neglected effects (such as Soret/Dufour) will be revisited and included (if necessary). The outcome will be a complete picture of the geometry of the reaction zone, and the proposed work will have important impacts on many natural phenomena and engineering applications: from energy generation to safety to astrophysics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.