Nonlinear response of a premixed low-swirl flame to acoustic excitation with large amplitude

Liu, Weijie; Xue, Ranran; Zhang, Liang; Qian, Yuping; Wang, Huiru

doi:10.1016/j.combustflame.2021.111733

Cited by 16 publications

(8 citation statements)

References 55 publications

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“…As the excitation frequency increased, a diminishing trend was evident in the harmonic flame response. This trend was consistent with the findings reported by Liu [14] regarding premixed flames. Specifically, under 20 Hz excitation, an evident harmonic response emerged at 40 Hz.…”

Section: Flame Responsesupporting

confidence: 93%

“…These POD results confirmed both the presence of harmonic flame response and its impact on flame oscillation patterns. Harmonic flame response has garnered considerable attention in research on the nonlinear response of premixed flames [12][13][14]35]. Notably, the phenomenon of harmonic response was observed in the non-premixed flame in this study as well.…”

Section: Flame Responsesupporting

confidence: 53%

“…Kim [13] observed similar phenomena in stratified premixed flames, finding a correlation between coherent vortex structure and harmonic flame response. Recently, Liu [14] examined low-swirl premixed flames' harmonic response over a wide range of perturbation amplitudes at different frequencies, attributing the response to the complex flame structure and fluctuating velocity-induced vortex interactions. Combined with flame dynamics analysis, shear layer instability due to acoustically induced vortices emerged as a significant factor in nonlinear flame response.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of Harmonic Response in Non-Premixed Swirling Combustion to Low-Frequency Acoustic Excitations

Bao,

Ji,

Pan

et al. 2023

Aerospace

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The propagation mechanism of flow disturbance under acoustic excitations plays a crucial role in thermoacoustic instability, especially when considering the effect of non-premixed combustion on heat release due to reactant mixing and diffusion. This relationship leads to a complex coupling between the spatial distribution of the equivalence ratio and the propagation mechanism of flow disturbance. In the present study, the response of a methane-air non-premixed swirling flame to low-frequency acoustic excitations was investigated experimentally. By applying Proper Orthogonal Decomposition (POD) analysis to CH* chemiluminescence images, the harmonic flame response was revealed. Large Eddy Simulation (LES) was utilized to analyze the correlation between the vortex motion within the shear layers and the harmonic response under non-reacting conditions at excitation frequencies of 20 Hz, 50 Hz, and 150 Hz. The results showed that the harmonic flame response was mainly due to the harmonic velocity pulsations within the shear layers. The acoustically induced vortices within the shear layer exhibited motion patterns susceptible to harmonic interference, with spatial distribution characteristics closely related to the oscillation modes of the non-premixed combustion.

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Section: Flame Responsesupporting

confidence: 93%

Section: Flame Responsesupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Investigation of Harmonic Response in Non-Premixed Swirling Combustion to Low-Frequency Acoustic Excitations

Bao,

Ji,

Pan

et al. 2023

Aerospace

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“…Specifically, under low-frequency forcing, the flame length exhibits a longer extent while the convective velocity experiences a decrease downstream of the flame. This convective velocity attenuation behavior has also been observed in premixed flames, as reported in references [46,51]. Consequently, such a variation of ucf causes significant deviations in Lf/λf and Stf at low-frequency conditions.…”

Section: The Dynamics Of Flame Responsesupporting

confidence: 75%

Characterizations of the Non-linear Responses of a Non-premixed Flame to the Low Frequency Acoustic Excitations

Pan¹,

Ji²,

Zhu³

2023

Preprint

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The heat release response of the flame to acoustic excitation is a critical factor for understanding combustion instability. In the present work, the nonlinear heat release response of a methane-air non-premixed flame to the low frequency acoustic excitations is experimentally investigated. The flame describing function (FDF) was measured based on the overall CH* chemiluminescence intensity and the velocity fluctuations obtained by two-microphone method. The CH* chemiluminescence images and the schlieren images were analyzed to reveal the mechanism of nonlinear response. The excitation frequency ranges from 10Hz to 120Hz. The forced relative velocity fluctuation amplitude ranges from 0.10 to 0.50. The corresponding flame Strouhal number (Stf) ranges from 0.43 to 4.67. The study has shown that the flame length responds more sensitively to changes in excitation amplitude when subjected to relatively high frequency excitations. The normalized flame length (Lf/D) decreases from 3.79 to 2.37 with the increase of excitation amplitude at excitation frequency of 100Hz. The number of oscillation zones along the flame increases with increasing excitation frequency, which is consistent with the increase of the Stf. The low-pass filtering characteristic of FDF is caused by the dispersion of multiple oscillation zones, as well as the cancellation effect of the adjacent oscillation zones under relatively high frequency excitation. The cancellation effect of the positive and negative oscillation zones with various Stf is main mechanism for the local gain peak and valley. When two adjacent oscillation regions have approximate amplitudes, the overall phase-lag becomes more sensitive to changes in excitation frequency and amplitude. This sensitivity leads to nonlinear anomalous changes in the phase-lag near the frequency corresponding to the gain valley. The calculated disturbance convection time is consistent with the measured time delay in the short flame scenario. Future research is necessary to establish whether the observed agreement occurs due to the oscillation zone consistently occurring proximate to the flame's center of mass, coupled with a precise determination of the average convective velocity.

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“…Specifically, under low-frequency forcing, the flame length exhibits a longer extent while the convective velocity experiences a decrease downstream of the flame. This convective velocity attenuation behavior has also been observed in premixed flames, as reported in references [46,51]. Consequently, such a variation of u cf causes significant deviations in L f /λ f and St f at low-frequency conditions.…”

Section: The Dynamics Of Flame Responsesupporting

confidence: 75%

Characterization of Nonlinear Responses of Non-Premixed Flames to Low-Frequency Acoustic Excitations

Pan

Zhu

2023

Applied Sciences

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The response of flames’ heat release to acoustic excitation is a critical factor for understanding combustion instability. In the present work, the nonlinear heat release response of a methane–air non-premixed flame to low-frequency acoustic excitations is experimentally investigated. The flame describing function (FDF) was measured based on the overall CH* chemiluminescence intensity and the velocity fluctuations obtained by the two-microphone method. The CH* chemiluminescence and schlieren images were analyzed for revealing the mechanism of nonlinear response. The excitation frequency ranges from 10 Hz to 120 Hz. The forced relative velocity fluctuation amplitude ranges from 0.10 to 0.50. The corresponding flame Strouhal number (Stf) ranges from 0.43 to 4.67. The study has shown that the flame length responds more sensitively to changes in excitation amplitude when subjected to relatively high-frequency excitations. The normalized flame length (Lf/D) decreases from 3.79 to 2.37 with the increase in excitation amplitude at an excitation frequency of 100 Hz. The number of oscillation zones along the flame increases with increasing excitation frequency, which is consistent with the increase in the Stf. The low-pass filtering characteristic of FDF is caused by the dispersion of multiple oscillation zones, as well as the cancellation effect of the adjacent oscillation zones under relatively high-frequency excitation. The main mechanism for the local gain peak and valley is the cancellation effect of positive and negative oscillation zones with various Stf. When two adjacent oscillation regions have similar amplitudes, the overall phase-lag becomes more sensitive to changes in excitation frequency and amplitude. This sensitivity leads to nonlinear anomalous changes in the phase-lag near the frequency corresponding to the gain valley. The calculated disturbance convection time is consistent with the measured time delay in the short flame scenario. Further research is required to determine whether the identified agreement is a result of the consistent occurrence of the oscillation zone in close proximity to the flame’s center of mass, in conjunction with a precise determination of the average convective velocity.

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Nonlinear response of a premixed low-swirl flame to acoustic excitation with large amplitude

Cited by 16 publications

References 55 publications

Investigation of Harmonic Response in Non-Premixed Swirling Combustion to Low-Frequency Acoustic Excitations

Investigation of Harmonic Response in Non-Premixed Swirling Combustion to Low-Frequency Acoustic Excitations

Characterizations of the Non-linear Responses of a Non-premixed Flame to the Low Frequency Acoustic Excitations

Characterization of Nonlinear Responses of Non-Premixed Flames to Low-Frequency Acoustic Excitations

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