scholarly journals Effects of swirler position on flame response and combustion instabilities

2021 ◽  
Author(s):  
Liangliang XU ◽  
Jianyi ZHENG ◽  
Guoqing WANG ◽  
Lei LI ◽  
Fei QI
Keyword(s):  
Combustion Instabilities ◽  
Flame Response

Open-Loop Control of Combustion Instabilities and the Role of the Flame Response to Two-Frequency Forcing

2011 ◽  
Author(s):  
Bernhard C´osic´ ◽  
Bernhard C. Bobusch ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Frequency Component ◽  
Open Loop ◽  
Operating Conditions ◽  
Combustion Instabilities ◽  
Open Loop Control ◽  
Elementary Model ◽  
Resonant Frequencies ◽  
Loop Control ◽  
Sinusoidal Input ◽  
Flame Response

Controlling combustion instabilities by means of open-loop forcing at non-resonant frequencies is attractive because neither a dynamic sensor signal nor a signal processor is required. On the other hand, since the mechanism by which this type of control suppresses an unstable thermoacoustic mode is inherently nonlinear, a comprehensive explanation for success (or failure) of open-loop control has not been found. The present work contributes to the understanding of this process in that it interprets open-loop forcing at non-resonant frequencies in terms of the flame’s nonlinear response to a superposition of two approximately sinusoidal input signals. For a saturation-type nonlinearity, the fundamental gain at one frequency may be decreased by increasing the amplitude of a secondary frequency component in the input signal. This effect is first illustrated on the basis of an elementary model problem. In addition, an experimental investigation is conducted at an atmospheric combustor test-rig to corroborate the proposed explanation. Open-loop acoustic and fuel-flow forcing at various frequencies and amplitudes is applied at unstable operating conditions that exhibit high-amplitude limit-cycle oscillations. The effectiveness of specific forcing parameters in suppressing self-excited oscillations is correlated with flame response measurements that include a secondary forcing frequency. The results demonstrate that a reduction in the fundamental harmonic gain at the instability frequency through the additional forcing at a non-resonant frequency is one possible indicator of successful open-loop control. Since this mechanism is independent of the system acoustics, an assessment of favorable forcing parameters, which stabilize thermoacoustic oscillations, may be based solely on an investigation of burner and flame.

Open-Loop Control of Combustion Instabilities and the Role of the Flame Response to Two-Frequency Forcing

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Bernhard Ćosić ◽  
Bernhard C. Bobusch ◽  
Jonas P. Moeck ◽  
Christian Oliver Paschereit
Keyword(s):  
Frequency Component ◽  
Open Loop ◽  
Operating Conditions ◽  
Combustion Instabilities ◽  
Open Loop Control ◽  
Elementary Model ◽  
Resonant Frequencies ◽  
Loop Control ◽  
Sinusoidal Input ◽  
Flame Response

Controlling combustion instabilities by means of open-loop forcing at non-resonant frequencies is attractive because neither a dynamic sensor signal nor a signal processor is required. On the other hand, since the mechanism by which this type of control suppresses an unstable thermoacoustic mode is inherently nonlinear, a comprehensive explanation for success (or failure) of open-loop control has not been found. The present work contributes to the understanding of this process in that it interprets open-loop forcing at non-resonant frequencies in terms of the flame’s nonlinear response to a superposition of two approximately sinusoidal input signals. For a saturation-type nonlinearity, the fundamental gain at one frequency may be decreased by increasing the amplitude of a secondary frequency component in the input signal. This effect is first illustrated on the basis of an elementary model problem. In addition, an experimental investigation is conducted at an atmospheric combustor test-rig to corroborate the proposed explanation. Open-loop acoustic and fuel-flow forcing at various frequencies and amplitudes is applied at unstable operating conditions that exhibit high-amplitude limit-cycle oscillations. The effectiveness of specific forcing parameters in suppressing self-excited oscillations is correlated with flame response measurements that include a secondary forcing frequency. The results demonstrate that a reduction in the fundamental harmonic gain at the instability frequency through the additional forcing at a non-resonant frequency is one possible indicator of successful open-loop control. Since this mechanism is independent of the system acoustics, an assessment of favorable forcing parameters, which stabilize thermoacoustic oscillations, may be based solely on an investigation of burner and flame.

Combustion Instabilities With Different Degrees of Premixedness in a Separated Dual-Swirl Burner

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Xinyao Wang ◽  
Xiao Han ◽  
Heng Song ◽  
Chi Zhang ◽  
Jianchen Wang ◽  
...  
Keyword(s):  
Equivalence Ratio ◽  
Large Scale ◽  
Convective Motion ◽  
Flame Surface ◽  
Mode Transition ◽  
Combustion Instabilities ◽  
Pressure Oscillations ◽  
Flame Response ◽  
Partially Premixed ◽  
Phase Angles

Abstract The effects of premixedness degrees on combustion instabilities of separated dual-swirl flames have been investigated experimentally in the Beihang Axial Swirler Independently Stratified (BASIS) burner. The degree of premixedness is modulated by the fuel split between two injection positions in the outer stream. In the spectra of pressure oscillations, both the frequency and amplitude are positively correlated with fuel split ratios under partially premixed conditions, and the mode transition between perfectly and partially premixed conditions has been observed. The location of perfectly premixed flames shows no obvious variation at different phase angles, only with a slightly wrinkling of the flame surface along the shear layer. Under partially premixed conditions, however, the flame is found to feature a large-scale periodic convective motion, accompanied by the obvious variation of heat releases due to the equivalence ratio oscillations. The local Rayleigh index map compares the thermoacoustic driving factors under perfectly and partially premixed conditions. The development of above convective motions under partially premixed conditions is explained by combining the variations of pressure oscillations and heat releases. An analysis of the thermoacoustic network and convective path is applied to explain the cause of the mode transition. The results show that the appearance of equivalence ratio oscillations and the elongated convective path under partially premixed conditions brings a longer delay time of the flame response, which could be the reason for the mode transition.

Dynamics of a Transversely Excited Swirling, Lifted Flame: Part I — Experiments and Data Analysis

2013 ◽  
Author(s):  
Michael Malanoski ◽  
Michael Aguilar ◽  
Vishal Acharya ◽  
Tim Lieuwen
Keyword(s):  
High Speed ◽  
Acoustic Excitation ◽  
Response Model ◽  
Combustion Instabilities ◽  
Excitation Field ◽  
Azimuthal Mode ◽  
Flow Response ◽  
Flame Response ◽  
Swirling Flame ◽  
Helical Mode

This paper is the first of two parts, and describes measurements of the response of a transversely forced, single nozzle, swirling flame. This study is motivated by combustion instabilities coupling with azimuthal combustor modes. Two different forcing configurations are applied, where the flame/nozzle are located at a pressure node and anti-node, respectively. High speed velocimetry and chemiluminescence measurements were made of the forced and unforced flow in multiple orthogonal planes, revealing both the axial and azimuthal development of the unsteady flow. Spectra and azimuthal mode decompositions of these data show the dominance of the m = 1 helical mode in the unforced flow. Depending upon the nature of the forcing, the flow response at the forcing frequency can be dominated by the axisymmetric, m = 0 mode, or the m = 1 mode. These results clearly show that the dominant fluid mechanic structures exciting flames during transverse instabilities varies from nozzle to nozzle, depending upon the phase characteristics of the acoustic excitation field. Part II of this paper uses these time averaged and fluctuating measurements as inputs to a flame response model of the unsteady global heat release fluctuations.

Effect of Cooling Liner on Acoustic Energy Absorption and Flame Response

2010 ◽  
Author(s):  
Umesh Bhayaraju ◽  
Johannes Schmidt ◽  
Karthik Kashinath ◽  
Simone Hochgreb
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Acoustic Waves ◽  
Bluff Body ◽  
Acoustic Energy ◽  
Combustion Instabilities ◽  
Acoustic Damping ◽  
Lean Combustion ◽  
Bias Flow ◽  
Flame Response

Gas turbine combustors with lean combustion injectors are prone to thermo-acoustic/combustion instabilities. Several passive techniques have been developed to control combustion instabilities, such as using Helmholtz resonators or viscous dampers using perforated liners that have potential for broadband acoustic damping. In this paper the role of single-walled cooling liners is considered in the damping of acoustic waves and on the flame transfer function in a sample bluff-body burner. Three liner geometries are considered: no bias flow (solid liner), normal effusion holes, and grazing effusion holes at 25° inclination. Cold flow experiments with speaker forcing are carried out to characterise the absorption properties of the liner and compared with an acoustic network model. The results show that whereas the bulk of the acoustic losses is due to the vortex recirculation zones, the liners contribute significantly to the absorption over a wide area of the frequency range. The flame transfer function gain is measured as a function of bias flow for a given operating condition of the burner. The experiments show that for the geometry considered, the global flame transfer function is little affected by cooling except in the case of the normal flow holes. Further analysis shows that whereas the total flame transfer function is not affected, the flame heat release becomes more spatially distributed along the axial length, and a 1D flame response shows distinct modes corresponding to the modal heat release locations.

scholarly journals Experimental Investigation of Injection-Coupled High-Frequency Combustion Instabilities

2020 ◽  
pp. 249-262
Author(s):  
Wolfgang Armbruster ◽  
Justin S. Hardi ◽  
Michael Oschwald
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Acoustic Resonance ◽  
Dynamic Mode Decomposition ◽  
Coupling Mechanism ◽  
Rocket Engines ◽  
Combustion Instabilities ◽  
High Speed Imaging ◽  
Flame Dynamics ◽  
Flame Response

Abstract Self-excited high-frequency combustion instabilities were investigated in a 42-injector cryogenic rocket combustor under representative conditions. In previous research it was found that the instabilities are connected to acoustic resonance of the shear-coaxial injectors. In order to gain a better understanding of the flame dynamics during instabilities, an optical access window was realised in the research combustor. This allowed 2D visualisation of supercritical flame response to acoustics under conditions similar to those found in European launcher engines. Through the window, high-speed imaging of the flame was conducted. Dynamic Mode Decomposition was applied to analyse the flame dynamics at specific frequencies, and was able to isolate the flame response to injector or combustion chamber acoustic modes. The flame response at the eigenfrequencies of the oxygen injectors showed symmetric and longitudinal wave-like structures on the dense oxygen core. With the gained understanding of the BKD coupling mechanism it was possible to derive LOX injector geometry changes in order to reduce the risks of injection-coupled instabilities for future cryogenic rocket engines.

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