Premixed Flame Response to Acoustic Waves in a Porous-Walled Chamber with Surface Mass Injection

2002 ◽  
Author(s):  
Wen-Wei Chu ◽  
Vigor Yang ◽  
Anand Vyas ◽  
Joseph Majdalani
Keyword(s):  
Acoustic Waves ◽  
Premixed Flame ◽  
Surface Mass ◽  
Mass Injection ◽  
Flame Response

Significance of the Direct Excitation Mechanism for High-Frequency Response of Premixed Flames to Flow Oscillations

2020 ◽  
Author(s):  
Vishal Acharya ◽  
Tim Lieuwen
Keyword(s):  
Heat Release ◽  
Acoustic Waves ◽  
Premixed Flames ◽  
Axial Flow ◽  
Flame Length ◽  
Excitation Mechanism ◽  
Direct Mechanism ◽  
Direct Excitation ◽  
Flow Disturbances ◽  
Flame Response

Abstract Premixed flames are sensitive to flow disturbances, which can arise from acoustic or vortical fluctuations. For transverse instabilities, it is known that a dominant mechanism for flame response is “injector coupling”, whereby pressure oscillations associated with transverse waves excite axial flow disturbances. These axial flow disturbances then excite heat release oscillations. The objective of this paper is to consider another mechanism — the direct sensitivity of the unsteady heat release to transverse acoustic waves, and to compare its significance relative to the induced axial disturbances, in a linear framework. The rate at which the flame adds energy to the disturbance field is quantified using the Rayleigh criterion and evaluated over a range of control parameters, such as flame length and swirl number. The results show that radial modes induce heat release fluctuations that always add energy to the acoustic field, whereas heat release fluctuations induced by mixed radial-azimuthal modes can add or remove energy. These amplification rates are then compared to the flame response from induced axial fluctuations. For combustor centered flames, these results show that the direct excitation mechanism has negligible amplification rates relative to the induced axial mechanism for radial modes. For transverse modes, the fact that the nozzle is located at a pressure node indicates that negligible induced axial velocity disturbances are excited; as such, the direct mechanism dominates. For flames that are not centered on pressure nodes, the direct mechanism for mixed-modes, dominates for certain nozzle locations and flame angles.

Premixed flame response to equivalence ratio perturbations

2010 ◽  
Vol 14 (5) ◽  
pp. 681-714 ◽  
Author(s):  
Shreekrishna ◽  
Santosh Hemchandra ◽  
Tim Lieuwen
Keyword(s):  
Equivalence Ratio ◽  
Premixed Flame ◽  
Flame Response

Response of Autoignition-Stabilized Flames to One-Dimensional Disturbances: Intrinsic Response

2021 ◽  
Author(s):  
Harish Subramanian Gopalakrishnan ◽  
Andrea Gruber ◽  
Jonas Moeck
Keyword(s):  
Flame Front ◽  
Acoustic Waves ◽  
Gas Turbines ◽  
Temperature Fluctuations ◽  
Feedback Mechanism ◽  
Stable Operation ◽  
One Dimensional ◽  
Flame Response ◽  
Mean Pressure ◽  
Stabilized Flames

Abstract Burning carbon-free fuels such as hydrogen in gas turbines promises power generation with reduced greenhouse gas emissions. A two-stage combustor architecture with an autoignition-stabilized flame in the second stage allows for efficient combustion of hydrogen fuels. However, interactions between the autoignition-stabilized flame and the acoustic field of the combustor may result in self-sustained oscillations of the flame front position and heat release rate, which severely affect the stable operation of the combustor. We study one such 'intrinsic' mode of interaction wherein acoustic waves generated by the unsteady flame travel upstream and modulate the incoming mixture resulting in flame front oscillations. In particular, we study the response of an autoignition-stabilized flame to upstream traveling acoustic disturbances in a one-dimensional configuration. We first present a numerical framework to calculate the response of autoignition-stabilized flames to acoustic and entropy disturbances in a one-dimensional combustor. The flame response is computed by solving the energy and species mass balance equations. We validate the framework with compressible direct numerical simulations. Lastly, we present results for the flame response to upstream traveling acoustic perturbations. The results show that autoignition-stabilized flames are highly sensitive to acoustic temperature fluctuations and exhibit a characteristic frequency-dependent response. Acoustic pressure and velocity fluctuations constructively or destructively superpose with temperature fluctuations, depending on the mean pressure and relative phase between the fluctuations. The findings of the present work are essential for understanding the intrinsic feedback mechanism in combustors with autoignition-stabilized flames.

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