Response of premixed flames to irrotational and vortical velocity fields generated by acoustic perturbations

Steinbacher, Thomas; Albayrak, Alp; Ghani, Abdulla; Polifke, Wolfgang

doi:10.1016/j.proci.2018.07.041

Cited by 14 publications

(8 citation statements)

References 22 publications

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“…For realistic gas expansion, the influence of the vortex structures on the flame perturbations is considerable only at the base of the flame. Similar conclusions were reached by the authors of the present paper for confined flames stabilized at a backwardfacing step [19]: Using a low-order model based on a decomposition approach [20,21], it was found that shear layer vorticity only has a negligible influence on the flame response.…”

Section: Introductionsupporting

confidence: 90%

“…Vorticity generated by acoustic-hydrodynamic mode conversion as well as by perturbations of the flame front, which is represented by a G-equation, may contribute to the latter. In this way, flame-flow interaction is taken into consideration, which is the essential novelty compared to previous studies reviewed above and our earlier work [19]. The validity of the model is cross-checked against high-fidelity CFD simulations.…”

Section: Introductionmentioning

confidence: 99%

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Convective Velocity Perturbations and Excess Gain in Flame Response as a Result of Flame-Flow Feedback

Steinbacher

Polifke

2022

Fluids

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Convective velocity perturbations (CVPs) are known to play an important role in the response of flames to acoustic perturbations and in thermoacoustic combustion instabilities. In order to elucidate the flow-physical origin of CVPs, the present study models the response of laminar premixed slit flames to low amplitude perturbations of the upstream flow velocity with a reduced order flow decomposition approach: A linearized G-equation represents the shape and heat release rate of the perturbed flame, while the velocity perturbation field is decomposed into irrotational and solenoidal contributions. The former are determined with a conformal mapping from geometry and boundary conditions, whereas the latter are governed by flame front curvature and flow expansion across the flame, which generates baroclinic vorticity. High-resolution CFD analysis provides values of model parameters and confirms the plausibility of model results. This flow decomposition approach makes it possible to explicitly evaluate and analyze the respective contributions of irrotational and solenoidal flows to the flame response, and conversely the effect of flame perturbations on the flow. The use of the popular ad hoc hypothesis of convected velocity perturbation is avoided. It is found that convected velocity perturbations do not result from immediate acoustic-to-hydrodynamic mode conversion, but are generated by flame-flow feedback. In this sense, models for flame dynamics that rely on ad-hoc models for CVPs do not respect causality. Furthermore, analysis of the flame impulse response reveals that for the configuration investigated, flame-flow feedback is also responsible for “excess gain” of the flame response, that is, the magnitude of the flame frequency response above unity.

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Section: Introductionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Convective Velocity Perturbations and Excess Gain in Flame Response as a Result of Flame-Flow Feedback

Steinbacher

Polifke

2022

Fluids

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“…Fleifil et al (1996) demonstrated that any flow perturbation normal to the flame surface disturbs the kinematic balance between flow and flame speeds and hence causes unsteady heat release rate. The flow perturbation due to plane acoustic waves at the flame front is one of the major contributions to thermoacoustic instabilities and is investigated extensively in the literature (see Schuller et al (2003), Blumenthal et al (2013) and Steinbacher et al (2019)). Similarly, axial and radial velocity perturbations resulting from inertial waves, respectively u z and u r in Eq.…”

Section: Solutionmentioning

confidence: 99%

Propagation speed of inertial waves in cylindrical swirling flows

2019

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Thermo-acoustic combustion instabilities arise from feedback between flow perturbations and the unsteady heat release rate of a flame in a combustion chamber. In the case of a premixed, swirl stabilized flame, an unsteady heat release rate results from acoustic velocity perturbations at the burner inlet on the one hand, and from azimuthal velocity perturbations, which are generated by acoustic waves propagating across the swirler, on the other. The respective time lags associated with these flow–flame interaction mechanisms determine the overall flame response to acoustic perturbations and therefore thermo-acoustic stability. The propagation of azimuthal velocity perturbations in a cylindrical duct is commonly assumed to be convective, which implies that the corresponding time lag is governed by the speed of convection. We scrutinize this assumption in the framework of small perturbation analysis and modal decomposition of the Euler equations by considering an initial value problem. The analysis reveals that azimuthal velocity perturbations in swirling flows should be regarded as dispersive inertial waves. As a result of the restoring Coriolis force, wave propagation speeds lie above and below the mean flow bulk velocity. The differences between wave propagation speed and convection speed increase with increasing swirl. A linear, time invariant step response solution for the dynamics of inertial waves is developed, which can be approximated by a concise analytical expression. This study enhances the understanding of the flame dynamics of swirl burners in particular, and contributes physical insight into the inertial wave dynamics in general.

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“…In the past decades, scholars have generally focused on flame instability and acoustic control during combustion, including thermoacoustic instability and oscillations in gas turbine combustion chambers and active control of flames [7][8][9][10][11]. Wang et al [12] developed nonlinear response patterns of laminar diffusion flames to external perturbations at different acoustic frequencies.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of the Behavior of Horizontally Buoyant Turbulent Jet Flames in Acoustic Waves

Wang,

Wang

2023

IJE

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Natural gas is most commonly transported by pipeline. However, leaks sometimes occur during transport, often leading to jet fires that cause substantial economic damage and property damage. It is therefore crucial to improve the efficiency of jet fire suppression. This paper focuses on the change of flame morphology of horizontal jet fires under different boundary conditions (acoustic pressure, frequency and jet exit velocity) and experimentally analyses the horizontal, vertical and trajectory length variation laws of the flame. Then a prediction model relating the horizontal length, vertical length and trajectory length of the horizontal jet flame under the action of acoustic waves is established.

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Response of premixed flames to irrotational and vortical velocity fields generated by acoustic perturbations

Cited by 14 publications

References 22 publications

Convective Velocity Perturbations and Excess Gain in Flame Response as a Result of Flame-Flow Feedback

Convective Velocity Perturbations and Excess Gain in Flame Response as a Result of Flame-Flow Feedback

Propagation speed of inertial waves in cylindrical swirling flows

Experimental Study of the Behavior of Horizontally Buoyant Turbulent Jet Flames in Acoustic Waves

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