TY - JOUR
T1 - Detailed unsteady dynamics of flame-flow interactions during combustion instability and its transition scenario for lean-premixed low-swirl hydrogen turbulent flames
AU - Shoji, Takeshi
AU - Tachibana, Shigeru
AU - Nakazumi, Yoshihiro
AU - Fujii, Ryota
AU - Masugi, Judai
AU - Yokomori, Takeshi
N1 - Funding Information:
The authors thank Terukazu Suzuki of EY Strategy and Consulting Co. Ltd. (a former master's student at Keio University) for assistance during data collection in these experiments and Professor Ryoichi Kurose, Abhishek L. Pillai, and Jun Nagao of Kyoto University for helpful discussions and insights.
Publisher Copyright:
© 2022 The Combustion Institute
PY - 2023/1
Y1 - 2023/1
N2 - This experimental study elucidates the unsteady dynamics of flame-flow interactions during unique thermoacoustic instability (TI) and the transition mechanism from stable combustion to TI for lean-premixed hydrogen turbulent jet flames in a low-swirl combustor (LSC), where a swirler assembly consists of an unswirled central region (CR) and an annular swirler region (SR). Simultaneous 200-kHz pressure fluctuation p’ measurements and 10-kHz OH* chemiluminescence imaging, as well as 40-kHz stereoscopic particle image velocimetry (SPIV) and two-dimensional PIV measurements for steady-state and transient data acquisitions, respectively, were conducted. The SPIV was performed in multiple planes to explore three-dimensional velocity fields. During TI, periodic flashback was possibly caused by significant axial velocity oscillations, resulting in the local mixture velocity falling below the turbulent flame speed. The large-scale vortex ring generated by the velocity oscillations caused axisymmetric radial velocity Vr oscillations with switching signs during the TI period. Similar to a typical low-swirl flow, the positive Vr away from the combustor axis created diverging flow, whereas unlike the typical flowfield, the negative Vr toward the combustor axis generated converging flow while flattening the axial velocity distributions, which was the signature phenomenon for this TI. Using the transient data and dynamic mode decomposition, variations in delay times between the mixture injection and its convection to a region with positive local Rayleigh indices were investigated. During stable combustion, the mixture jet from the SR predominantly induced thermoacoustic coupling (TC). As the combustion transitioned into the TI, the mixture jet from the CR began to induce TC and, eventually, achieved predominance in inducing TC during fully evolved TI. The transition from the SR jet- into CR jet-dominant TI arising from the dynamic flame-flow interactions resulted from the inherent physical characteristics of hydrogen flames, thereby yielding the larger p’ amplitude compared to typical TIs.
AB - This experimental study elucidates the unsteady dynamics of flame-flow interactions during unique thermoacoustic instability (TI) and the transition mechanism from stable combustion to TI for lean-premixed hydrogen turbulent jet flames in a low-swirl combustor (LSC), where a swirler assembly consists of an unswirled central region (CR) and an annular swirler region (SR). Simultaneous 200-kHz pressure fluctuation p’ measurements and 10-kHz OH* chemiluminescence imaging, as well as 40-kHz stereoscopic particle image velocimetry (SPIV) and two-dimensional PIV measurements for steady-state and transient data acquisitions, respectively, were conducted. The SPIV was performed in multiple planes to explore three-dimensional velocity fields. During TI, periodic flashback was possibly caused by significant axial velocity oscillations, resulting in the local mixture velocity falling below the turbulent flame speed. The large-scale vortex ring generated by the velocity oscillations caused axisymmetric radial velocity Vr oscillations with switching signs during the TI period. Similar to a typical low-swirl flow, the positive Vr away from the combustor axis created diverging flow, whereas unlike the typical flowfield, the negative Vr toward the combustor axis generated converging flow while flattening the axial velocity distributions, which was the signature phenomenon for this TI. Using the transient data and dynamic mode decomposition, variations in delay times between the mixture injection and its convection to a region with positive local Rayleigh indices were investigated. During stable combustion, the mixture jet from the SR predominantly induced thermoacoustic coupling (TC). As the combustion transitioned into the TI, the mixture jet from the CR began to induce TC and, eventually, achieved predominance in inducing TC during fully evolved TI. The transition from the SR jet- into CR jet-dominant TI arising from the dynamic flame-flow interactions resulted from the inherent physical characteristics of hydrogen flames, thereby yielding the larger p’ amplitude compared to typical TIs.
KW - Dynamic mode decomposition
KW - High-speed stereoscopic PIV
KW - Lean-premixed hydrogen flame
KW - Low-swirl combustor
KW - Thermoacoustic instability
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U2 - 10.1016/j.proci.2022.08.126
DO - 10.1016/j.proci.2022.08.126
M3 - Article
AN - SCOPUS:85143270682
SN - 1540-7489
VL - 39
SP - 4741
EP - 4750
JO - Proceedings of the Combustion Institute
JF - Proceedings of the Combustion Institute
IS - 4
ER -