Comments on the low frequency radiation impedance of a duct exhausting a hot gas

Hirschberg, Avraham; Hoeijmakers, Maarten

doi:10.1121/1.4885540

Cited by 6 publications

(3 citation statements)

References 26 publications

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“…Furthermore, it is seen that irrotational velocity perturbations are large near the flame base, and weaken significantly towards the tip of the flame. Note that these results fully corroborate the findings of our earlier study [19], which did not rely on a Kutta panel, but instead introduced a simple estimate of the total circulation created by a separating vortex sheet during a time interval ∆t [56,58]:…”

Section: Harmonic Forcingsupporting

confidence: 86%

“…The position of the mean flow shear layer is taken from the high-fidelity CFD simulations described in Section 2.3. The transport velocity for vorticity along this line is set to the fixed value of u blk /2 [56]. Equation ( 23) is integrated in time relying on an explicit Euler method together with a first-order upwind discretization scheme for the advection and a second-order central scheme for the diffusion term.…”

Section: Unidirectional Couplingmentioning

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: Harmonic Forcingsupporting

confidence: 86%

Section: Unidirectional Couplingmentioning

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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“…Only the pressure reflection coefficient has been addressed throughout this article. Apart from it there is the energy reflection coefficient R E , for which an additional Mach number dependence takes place (Hirschberg, Hoeijmakers, 2014):…”

Section: Discussionmentioning

confidence: 99%

Archives of Acoustics

Hruška

Dlask

2021

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The reflection coefficient of the open end belongs among the essential parameters in the physical description of a flue organ pipe. It leads directly to practical topics such as the pipe scaling. In this article, sound propagation is investigated inside an organ pipe with the most intense mean flow that is achievable under musically relevant conditions. A theoretical model is tested against the experimental data to obtain a suitable formula for the reflection coefficient when a non-negligible flow through the open end is considered. The velocity profile is examined by means of particle image velocimetry. A fully developed turbulent profile is found and interactions of the acoustic boundary layer with the turbulent internal flow are discussed. A higher value of the end correction than expected from the classical result of Levine and Schwinger is found, but this feature shall be associated with the pipe wall thickness rather than the mean flow effects.

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

Steinbacher

Albayrak

Ghani

et al. 2019

Proceedings of the Combustion Institute

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Comments on the low frequency radiation impedance of a duct exhausting a hot gas

Cited by 6 publications

References 26 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

Archives of Acoustics

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

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