Pocket formation and behavior in turbulent premixed flames

Abstract

Pocket formation is an important characteristic of turbulent premixed flames and understanding pocket behavior is key to developing high-fidelity numerical combustion models. In this study, a dual-burner experiment is used to study pockets in single-and dual-flame configurations and synchronized high-speed OH-planar laser-induced fluorescence and stereoscopic-particle image velocimetry imaging techniques are implemented to track flame pockets and the surrounding flow field. Statistical analysis of pocket origin and fate is performed using a novel tracking algorithm incorporating non-rigid image registration. Results show that pocket formation rates increase as a function of increasing inlet turbulence level; reactant pocket formation increases as a function of downstream distance, whereas product pocket formation decreases. Tracking reactant pocket lifetime shows that a majority of these pockets burn out and displacement speeds are characterized. Product pockets usually merge with the main flame surface, which could have an impact on local flame structure and propagation. Results presented in this study show that pocket behavior in turbulent flames can change local flame dynamics and it is important to capture these effects in sub-grid scale combustion models to accurately predict flame behavior.

Hybrid algorithm for the detection of turbulent flame fronts

“… 2017 ) or statistically based on the image histogram (Tyagi et al. 2020 ; Halter et al. 2009 ; Malbois et al.…”

“…Hence, if edge-preserving filters are to be used jointly with segmentation as has been done in a handful past investigations (Sweeney and Hochgreb 2009 ; Tyagi et al. 2019 , 2020 ; Malbois et al. 2019 ), caution must be exercised to avoid erroneous flame fronts.…”

“…Other difficulties stem from the convoluted nature of turbulent flames, often featuring a number of reactant and product pockets in the corrugated flamelet regime (Tyagi et al. 2019 , 2020 ). Additional challenges arise when thermodiffusively unstable (i.e., lean hydrogen/air) flames are investigated, which feature a wide range of cellular structures and thin elongated fingers (Berger et al.…”

Data-driven Analysis of Turbulent Flame Images

“…Enhanced turbulent burning velocity leads to a thickening of the flame brush and rapid consumption of unburned reactant pockets near the flame tip [8]. Pocket formation and consumption processes have substantial implications in the development of accurate Large Eddy Simulation (LES) models based on their size in relation to the turbulence length scales including the Taylor microscale and the integral scale [9,10]. Unburned pocket formation and consumption at the tip of a Bunsen flame [11,12], and turbulent jet premixed flames [8,13,14] have been observed.…”