Turbulence-Driven Blowout Instabilities of Premixed Bluff-Body Flames

Abstract

Bluff-body flame instabilities are experimentally investigated under varying turbulence conditions during lean blowout. For all turbulence conditions, the blowout process is induced through a temporal reduction of the fuel flow rate to capture the flame-flow dynamics approaching blowout. Simultaneous high-speed particle image velocimetry (PIV), stereoscopic PIV, and C 2 */CH* chemiluminescence imaging are employed, along with an independent CH* imaging system, to capture flame-flow instabilities. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) techniques are used to identify prominent flame oscillations and evaluate recurring spatiotemporal modes during blowout. The results reveal that the dominant flame oscillations and wrinkling characteristics are directly dependent on the turbulence conditions in the combustor. Specifically, the flame-flow oscillations are strongly coupled with the integral length scales, which were able to collapse the oscillation frequencies to a unified value. The turbulence-driven flameflow oscillations are shown to largely impact the magnitude, temporal evolution, and oscillatory behavior of the flame strain rate. As the turbulence intensity is increased, the oscillation of the flame strain rate increases in frequency, making it more likely for localized extinctions to occur. Additionally, the magnitude of the flame strain rate increases at high turbulence intensities and accelerates the lean blowout process.

Spectral analysis of OH-PLIF snapshots of a bluff body wake

“…In the field of combustion, (Kostka et al, 2012) provided an analysis of the bluff body wake using high-speed chemiluminescence images. Since then, several papers can be found in the literature that involve the utilization of the proper orthogonal decomposition on high-speed flow and flame imagery (Blanchard et al, 2014;Caswell et al, 2014;Emerson, 2013;Monfort, 2015;Morales et al, 2021;Roy et al, 2015;Shaw et al, 2019;Wickersham et al, 2014;Yang et al, 2020).…”