• What is the problem/issue being addressed?
The characterization of the interactions between the flame and turbulence is essential in mixing and combustion. In the last decades, the wrinkling of a flame or of a scalar field due to turbulence has been envisioned as the result of vortices interacting with the flame front. However, this preconceived notion should be substantiated through theoretical studies and numerical simulations to accurately understand the nature of the flame-turbulence interactions that are responsible for flame strain and local quenching events. In a turbulent flow, fluid from the irrotational region becomes turbulent through the propagation of the Turbulent/Non-Turbulent (T/NT) enstrophy interface. In many T/NT interfaces, large scale eddy motion folds the separating surface and ingest or engulf irrotational fluid into the turbulent region; subsequently, this ‘ingested’ irrotational fluid is ‘digested’ and incorporated to the turbulent region by viscous diffusion of vorticity at small scales. These entrainment mechanisms have been studied for the past decades. However, the description and quantification of the importance of small and large scales contributing to entrainment mechanisms are still unsolved. Thus, this project, ‘Interfaces in Turbulent Premixed Flames’ (ITPF – EU Project Nº 706672), aims at improving the physical understanding of the entrainment of hot reacted products in annular co-flows of turbulent premixed flames into jets of fresh reactants. This is an essential point in combusting turbulent free shear flows, because a better knowledge of the dynamics of T/NT and scalar interfaces would lead to better predictions of flame instabilities and field structures.
• Why is it important for society?
The findings obtained during the ITPF project have had a significant impact and implications in the combustion community. These results can help us understand how the interaction between the scalar and enstrophy interfaces strongly influences the local scalar geometry. A comprehension of these physical mechanisms should better guide the formulation of sound and accurate mixing and combustion models. This can eventually help generating clean, save and cost-effective combustion systems, for burning fossil and sustainable fuels to provide power, heat and transportation.
• What are the overall objectives?
This project aims at understanding the physics of entrainment in turbulent premixed flames. This research characterizes the entrainment processes through the study and comparison of the T/NT enstrophy interface and scalar interfaces. This study applies statistical and topological methods to identify the contributions to entrainment and engulfment through analyzing flow and scalar fields in high-resolution simulations of turbulent premixed flames. This project develops and post-processes Direct Numerical Simulations (DNS) of turbulent premixed flames and analyzes their results, in conjunction with Large Eddy Simulations (LES). A smart combination of DNSs and LESs permits to unveil contributions of large and small structures to the entrainment process, to better comprehend physical mechanisms and to formulate sound and accurate mixing and combustion models.
