Thermoacoustic Flame Response of Swirl Flames

Krebs, Werner; Hoffmann, Stefan; Prade, Bernd; Lohrmann, Martin; ̈chner, Horst Bu

doi:10.1115/gt2002-30065

Cited by 13 publications

(8 citation statements)

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“…The structure of this transfer function holds also for turbulent flames, see e.g. [76,73,71,56]. The fluctuating axial velocity u ax can be expressed as a linear transfer function of the pressure p in the annular chamber, as long as only one mode, or two degenerate modes, oscillate, as discussed in detail in [44].…”

Section: Flame Modelmentioning

confidence: 99%

The effect of the flame phase on thermoacoustic instabilities

Ghirardo¹,

Juniper

Bothien³

2018

Combustion and Flame

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This paper concerns the influence of the phase of the heat release response on thermoacoustic systems. We focus on one pair of degenerate azimuthal acoustic modes, with frequency ω 0. The same results apply for an axial acoustic mode. We show how the value φ 0 and the slope −τ of the flame phase at the frequency ω 0 affects the boundary of stability, the frequency and amplitude of oscillation, and the phase φ qp between heat release rate and acoustic pressure. This effect depends on φ 0 and on the nondimensional number τ ω 0 , which can be quickly calculated. We find for example that systems with large values of τ ω 0 are more prone to oscillate, i.e. they are more likely to have larger growth rates, and that at very large values of τ ω 0 the value φ 0 of the flame phase at ω 0 does not play a role in determining the system's stability. Moreover for a fixed flame gain, a flame whose phase changes rapidly with frequency is more likely to excite an acoustic mode. We propose ranges for typical values of nondimensional acoustic damping rates, frequency shifts and growth rates based on a literature review. We study the system in the nonlinear regime by applying the method of averaging and of multiple scales. We show how to account in the time domain for a varying frequency of oscillation as a function of amplitude, and validate these results with extensive numerical simulations for the parameters in the proposed ranges. We show that the frequency of oscillation ω B and the flame phase φ qp at the limit cycle match the respective values on the boundary of stability. We find good agreement between the model and thermoacoustic experiments, both in terms of the ratio ω B /ω 0 and of the phase φ qp , and provide an interpretation of the transition between different thermoacoustic states of an experiment. We discuss the effect of neglecting the component of heat release rate not in phase with the pressure p as assumed in previous studies. We show that this component should not be neglected when making a prediction of the system's stability and amplitudes, but we present some evidence that it may be neglected when identifying a system that is unstable and is already oscillating

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Section: Flame Modelmentioning

confidence: 99%

The effect of the flame phase on thermoacoustic instabilities

Ghirardo¹,

Juniper

Bothien³

2018

Combustion and Flame

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“…More details about the validation have been recently published by Krebs et al (2002). A 60" C F D model of the test rig is shown in Figure 11.…”

Section: Validation Of the Numerical Approachmentioning

confidence: 99%

Thermoacoustic Stability Chart for High-Intensity Gas Turbine Combustion Systems

Krebs

Flohr

Prade

et al. 2002

Combustion Science and Technology

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140

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The operating range of heavy duty gas turbines that feature lean premixed combustion to achieve low NO, emissions is limited by thermoacoustic oscillations. T o extend the operational envelope of the gas turbine, passive means have to be developed to suppress thermoacoustic instabilities. In order to develop passive means the complex interaction between acoustics and thermal heat release has to be taken into account. A new stability chart applicable to the qualification of industrial design has been developed that accounts for the acoustic properties of the combustion system including its boundary conditions and the flame response data. The method has been validated using detailed measurements of the eigenmodes in an operating gas turbine as well as experimental data from component test rigs. An explanation is given of the significant extension of the operation envelope of the gas turbine a s an effect of cylindrical extensions to the burner nozzle.

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“…[19,20]. However, for the response F φ to equivalence ratio fluctuations, previous work has always assumed that a dispersion of convective time delays will result in a low-pass filter behaviour with |F φ | < 1 for frequencies ω > 0 [21][22][23][24]. An explanation of the present result is developed in the next section.…”

Section: Flame Frequency Responsementioning

confidence: 81%

“…This argument also makes clear why approaches using steady state CFD simulation to determine F φ simply as "fuel transport time lag distributions" [21,22,24,27,28] are not able to capture this effect: these methods, no matter whether they use an Eulerian or Lagrangian approach to model the convective transport of fuel to the flame front, assume a fixed position of the flame and therefore a constant flame surface area. The reduction in flame surface due to "front kinematics", which is responsible for the undershoot in the UIR φ and therefore also for the excess gain of F φ , cannot be properly described with such modelling strategies.…”

Section: Flame Response To Equivalence Ratio Fluctuations At the Burnmentioning

confidence: 99%

Dynamics of Practical Premixed Flames, Part II: Identification and Interpretation of CFD Data

Huber

Polifke

2009

International Journal of Spray and Combustion Dynamics

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In Part I of this paper, a multiple-input, single-output (MISO) model for the dynamics of practical premixed flames has been proposed. A corresponding method for identification of model coefficients was developed and validated against test data generated with a linear time-domain model, designed to be qualitatively representative of a practical premix burner.The method for system identification of a MISO model is now applied to time series data generated with Computational Fluid Dynamics (CFD) simulation in the presence of broadband forcing. The CFD model represents a generic, practical premixed swirl burner with multiple fuel injection stages. Fuel injectors are assumed to be acoustically "non-stiff ", such that pressure fluctuations will modulate the fuel mass flow rates. The flame dynamics is therefore influenced by fluctuations of the equivalence ratio as well as the mass flow rate of premixture at the burner exit.Results obtained demonstrate that system identification based on correlation analysis is well capable of differentiating between the various interaction mechanisms. Unit impulse and flame transfer functions corresponding to different signal-response relations can be determined in a quantitative manner from a single CFD run. A detailed analysis and physical interpretation of the response functions has been carried out. The results allow to draw non-trivial conclusions concerning a) the interactions of flame front kinematics and equivalence ratio fluctuations and b) flame transfer functions with an amplitude above unity.

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Thermoacoustic Flame Response of Swirl Flames

Cited by 13 publications

References 0 publications

The effect of the flame phase on thermoacoustic instabilities

The effect of the flame phase on thermoacoustic instabilities

Thermoacoustic Stability Chart for High-Intensity Gas Turbine Combustion Systems

Dynamics of Practical Premixed Flames, Part II: Identification and Interpretation of CFD Data

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