Freestream and shear layer effects in bluff-body-stabilized turbulent premixed flames

Abstract

The effects of low and high approach flow turbulence levels on a large-scale, confined, premixed bluff-body-stabilized flame are experimentally characterized. The flame and flow are imaged using simultaneous 10-kHz-rate formaldehyde (CH2O) planar laser-induced fluorescence (PLIF), hydroxyl (OH) PLIF, particle image velocimetry (PIV), and OH* chemiluminescence. Elevated approach flow turbulence intensities of 16 % as compared to a lower value of 3 % affects the global and local flame and flow. The elevated approach flow turbulence results in a 22 % reduction in the length of the recirculation zone, despite the mean flame and mean shear layer locations being similar for both approach flow turbulence levels. Increasing the approach flow turbulence intensity does not lead to the mean flame position moving further into the reactant freestream. Both approach flow turbulence levels result in a similar growth of the flame brush thickness moving downstream until approximately 1.5 bluff-body widths, after which the flame brush for the low and high approach flow turbulence case stops growing and continues to linearly increase, respectively. This study describes the mechanisms by which high approach flow turbulence affects the global and local flame and emphasizes that the turbulent flame characteristics are influenced not only by the freestream approach flow turbulence but also by the bluff-body shear layers, recirculation zone, and wake.