The role of flow confinement on turbulent kinetic energy transfer across premixed flames

Abstract

The interaction between turbulent flows and premixed flames remains a significant topic of interest for improved modeling efforts and the advancement of clean and efficient combustion systems. Due to the challenging nature of the problem, the majority of studies related to turbulence-flame interactions have been conducted with unconfined numerical simulations or unconfined experimental burners. This paper describes the effects of flow confinement on the dynamics of turbulent reacting flows. An experimental premixed bluff-body combustion facility is operated under confined and unconfined conditions to understand the subsequent impact on the evolution of the turbulent reacting flow field across the flame. High-speed particle image velocimetry and chemiluminescence diagnostics are simultaneously employed to identify the flame front and capture turbulent velocity fields. The results show that the unconfined flame follows the classical description of turbulence evolution across the flame, in which turbulent fluctuations are dampened on the product side of the flame. In contrast, the opposite trend is observed for the confined configuration, and turbulent fluctuations are augmented by the reaction. The difference between the two cases is attributed to flow expansion and mean pressure gradients, which alters the balance between flame-generated turbulence and viscous dampening effects. Ultimately, the results provide a new perspective of premixed turbulent reacting flows and simultaneously highlight the importance of acquiring data in environments that better replicate practical combustion systems.