Analysis for Combustion Instability and Stabilization Characteristics in a Swirled Premixed Combustor With a Slotted Plate

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Seungtaek Oh ◽  
Jaehyeon Kim ◽  
Yongmo Kim
Keyword(s):  
Neural Network ◽  
Combustion Instability ◽  
Perforated Plate ◽  
Frequency Range ◽  
Describing Function ◽  
Extended Range ◽  
Average Absorption Coefficient ◽  
New Methodologies ◽  
Slotted Plate ◽  
Flame Describing Function

In this study, new methodologies are introduced to analyze combustion instability in a lab-scale swirled combustor. First, with the help of radial basis function neural network (RBFNN), the flame describing function (FDF) is effectively modeled from a limited number of experimental data. This neural-network-based FDF method is able to generate more refined FDF data in an extended range. In addition, instead of a perforated plate with round holes, a slotted plate is utilized as a stabilization device. In this approach, the acoustic impedance of a slotted plate is modeled by the Dowling approach, and the dimensions of a slotted plate are optimized by simulated annealing (SA) algorithm to get the highest average absorption coefficient in a given frequency range. The present RBFNN-based FDF approach yields the reasonably good agreements with the measurements in terms of the limit-cycle velocity perturbation ratio and resonant frequency. It is also found that a slotted plate optimized by SA algorithm is quite effective to attenuate combustion instability. Numerical results obtained in this study confirm that these new methodologies are quite reliable and widely applicable for the analysis of combustion instability encountered in practical combustion systems.

Nonlinear Flame Describing Function Analysis of Galloping Limit Cycles Featuring Chaotic States in Premixed Combustors

2012 ◽  
Author(s):  
Frédéric Boudy ◽  
Daniel Durox ◽  
Thierry Schuller ◽  
Sébastien Candel
Keyword(s):  
Limit Cycle ◽  
Limit Cycles ◽  
Function Analysis ◽  
Perforated Plate ◽  
Operating Conditions ◽  
Nonlinear Prediction ◽  
Constant Amplitude ◽  
Describing Function ◽  
Flame Describing Function ◽  
Velocity Pressure

Nonlinear prediction of combustion instabilities in premixed systems is undertaken on a generic configuration featuring an adjustable feeding manifold length, a multipoint injector composed of a perforated plate and a flame confinement tube. By changing the feeding manifold or flame tube lengths, the system exhibits different types of combustion regimes for the same flow operating conditions. Velocity, pressure and heat release rate measurements are used to examine oscillations during unstable operation. For many operating conditions, a limit cycle is reached at an essentially fixed oscillation frequency and quasi-constant amplitude. In another set of cases, the system features other types of oscillations characterized by multiple frequencies, amplitude modulation and irregular bursts which can be designated by “galloping” limit cycles or GLC. These situations are explored in this article. Imaging during GLCs indicates that the flame is globally oscillating but that the cycle is irregular. Prediction of these special oscillation states is tackled within the Flame Describing Function (FDF) framework. It is shown that it is possible to predict with a reasonable degree of agreement the ranges where a quasi-constant amplitude limit cycle will be established and ranges where the oscillation will be less regular and take the form of a galloping limit cycle. It is found that the FDF analysis also provides indications on the bounding levels of the oscillation envelope in the latter case.

scholarly journals Combining a Helmholtz solver with the flame describing function to assess combustion instability in a premixed swirled combustor

2013 ◽  
Vol 160 (9) ◽  
pp. 1743-1754 ◽  
Author(s):  
Camilo Fernando Silva ◽  
Franck Nicoud ◽  
Thierry Schuller ◽  
Daniel Durox ◽  
Sebastien Candel
Keyword(s):  
Combustion Instability ◽  
Describing Function ◽  
Flame Describing Function

Identification of the Flame Describing Function of a Premixed Swirl Flame from LES

2012 ◽  
Vol 184 (7-8) ◽  
pp. 888-900 ◽  
Author(s):  
H. J. Krediet ◽  
C. H. Beck ◽  
W. Krebs ◽  
S. Schimek ◽  
C. O. Paschereit ◽  
...  
Keyword(s):  
Describing Function ◽  
Flame Describing Function ◽  
Swirl Flame

scholarly journals Flame Dynamics Intermittency in the Bi-Stable Region Near a Subcritical Hopf Bifurcation

2017 ◽  
Author(s):  
D. Ebi ◽  
A. Denisov ◽  
G. Bonciolini ◽  
E. Boujo ◽  
N. Noiray
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Acoustic Pressure ◽  
Oscillation Amplitude ◽  
Stable Region ◽  
Describing Function ◽  
Acoustic Damping ◽  
Intermittent Behavior ◽  
Flame Describing Function

We report experimental evidence of thermoacoustic bi-stability in a lab-scale turbulent combustor over a well-defined range of fuel-air equivalence ratios. Pressure oscillations are characterized by an intermittent behavior with “bursts”, i.e. sudden jumps between low and high amplitudes occurring at random time instants. The corresponding probability density functions of the acoustic pressure signal show clearly separated maxima when the burner is operated in the bi-stable region. A flame describing function, which links acoustic pressure to heat release rate fluctuations, is estimated at the modal frequency from simultaneously recorded flame chemiluminescence and acoustic pressure. The representation of its statistics is new and particularly informative. It shows that this describing function is characterized, in average, by a nearly constant gain and by a significant drift of the phase as function of the oscillation amplitude. This finding suggests that the bi-stability does not result from an amplitude-dependent balance between flame gain and acoustic damping, but rather from the non-constant phase difference between the acoustic pressure and the coherent fluctuations of heat release rate.

Utilizing Hollow-Structured Bamboo as Natural Sound Absorber

2015 ◽  
Vol 40 (4) ◽  
pp. 601-608 ◽  
Author(s):  
Azma Putra ◽  
Fazlin Abd Khair ◽  
Mohd Jailani Mohd Nor
Keyword(s):  
Absorption Coefficient ◽  
Hollow Structure ◽  
Front Surface ◽  
Normal Incidence ◽  
Frequency Range ◽  
Peak Absorption ◽  
Natural Sound ◽  
Average Absorption Coefficient ◽  
Lower Frequency Range ◽  
Bamboo Structure

AbstractStudies to find alternative low environmental-impact materials for acoustic absorbers are still progressing, particularly those originated from natural materials. However, most of the established works are mainly focused on the fibrous-type absorbers. Discussion on the non-fibrous-type absorbers is still lacking and this therefore becomes the objective of this paper. Use of bamboo by utilizing its hollow structure to absorb sound energy is discussed here. The normal incidence absorption coefficient was measured based on the length and diameter of the bamboo, as well as different arrangement of the bamboo structure subjected to the incidence sound, namely, axial, transverse, and crossed-transverse arrangements. The trend of absorption coefficient appears in peaks and dips at equally spacing frequencies. For all arrangements the peak of absorption can reach above 0.8. Introducing an air gap behind the bamboo shifts the peak absorption to lower frequency. Covering the front surface of the absorber improves the sound absorption coefficient for axial arrangement by widening the frequency range of absorption also towards lower frequency range. The transverse arrangement is found to have average absorption coefficient peaks of 0.7 above 1.5 kHz. By arranging the bamboo structure with crossed-transverse arrangement, the suppressed absorption peaks in normal transverse arrangement can be recovered.

Describing Function Analysis of Limit Cycles in a Multiple Flame Combustor

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Frédéric Boudy ◽  
Daniel Durox ◽  
Thierry Schuller ◽  
Grunde Jomaas ◽  
Sébastien Candel
Keyword(s):  
Transfer Function ◽  
Limit Cycle ◽  
Limit Cycles ◽  
Function Analysis ◽  
Combustion Instabilities ◽  
Describing Function ◽  
Variable Size ◽  
Theoretical Predictions ◽  
Flame Describing Function ◽  
Oscillation Frequencies

A recently developed nonlinear flame describing function (FDF) is used to analyze combustion instabilities in a system where the feeding manifold has a variable size and where the flame is confined by quartz tubes of variable length. Self-sustained combustion oscillations are observed when the geometry is changed. The regimes of oscillation are characterized at the limit cycle and also during the onset of oscillations. The theoretical predictions of the oscillation frequencies and levels are obtained using the FDF. This generalizes the concept of flame transfer function by including dependence on the frequency and level of oscillation. Predictions are compared with experimental results for two different lengths of the confinement tube. These results are, in turn, used to predict most of the experimentally observed phenomena and in particular, the correct oscillation levels and frequencies at limit cycles.

Truss Structure Health Monitoring Based on Electromechanical Impedance Method

2013 ◽  
Vol 330 ◽  
pp. 357-363
Author(s):  
Cun Fu He ◽  
Xiao Ming Cai ◽  
Shen Yang ◽  
Zeng Hua Liu ◽  
Bin Wu
Keyword(s):  
Neural Network ◽  
Health Monitoring ◽  
Truss Structure ◽  
Truss Structures ◽  
Impedance Method ◽  
Nonparametric Model ◽  
Impedance Spectra ◽  
Frequency Range ◽  
Electromechanical Impedance ◽  
Piezoelectric Elements

Truss structure is widely used in civil engineering applications for its advantages of easy transportation, convenient assembly and uniform loading. However, it is difficult to achieve real-time health monitoring because of connection diversity and complexity of truss structures. As a novel structural health monitoring technique, electro-mechanical impedance method could monitor the health state of one structure by measuring the spectra of impedance or admittance of the piezoelectric elements, which are bonded on the surface of this structure. This approach has the advantages of nonparametric model analysis, easy sensor installation and high local sensitivity, especially in sensitive frequency range. The damage information, which is tested and recorded by using electromechanical impedance method, could convert into intuitive results through neural network because of its good ability for nonlinear mapping. In this paper, a three-layer assembly truss structure was chosen as experimental object, piezoelectric elements were bonded on structure joints to measure structural impedance spectra, the change of these structural impedance spectra was tested and recorded under high frequency excitations when different truss bars were loosed, and then, one back-propagation (BP) neural network was built and trained by this damage information, which were treated as input samples. These results show that the sensitivity of impedance method is not the same to different frequency range and trained neural network could quickly identify loosen truss bars.

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