Discussion of laser interferometric vibrometry for the determination of heat release fluctuations in an unconfined swirl-stabilized flame

Greiffenhagen, Felix; Peterleithner, Johannes; Woisetschläger, Jakob; Fischer, Andreas; Gürtler, Johannes; Czarske, Jürgen

doi:10.1016/j.combustflame.2018.12.019

Cited by 8 publications

(13 citation statements)

References 26 publications

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“…There are several sources which may change density, such as fluctuations in heat release or pressure and turbulence, but also density gradients travelling with the flow will be detected as fluctuations in density via LIV. If other sources are neglectable density fluctuations can be used to calculate local and global fluctuations in heat release (Greiffenhagen et al 2019). Via tomographic reconstruction also local data can be derived with high accuracy.…”

Section: Introductionmentioning

confidence: 99%

“…In the next paragraphs a short overview is given, how fluctuations in density, heat release and pressure are linked to each other. A more detailed discussion can be found in Greiffenhagen et al (2019).…”

Section: Introductionmentioning

confidence: 99%

“…The substantial derivative of density consists of a local time dependent term and a convective part . Using a single-point LIV system (Greiffenhagen et al 2019), thermoacoustic oscillations had to be excited by a siren to enable spatio-temporal correlations between the scanned positions. Such a triggered scanning LIV is necessary to obtain the convection term in above equation.…”

Section: Introductionmentioning

confidence: 99%

“…Two measurement methods provided the necessary data, namely background-oriented schlieren (BOS) technique records mean local density or temperature, and spectroscopy records local equivalence ratio. The latter is also used to calculate the species-dependent local Gladstone–Dale constants, relating density and refractive index (Greiffenhagen et al 2019).…”

Section: Introductionmentioning

confidence: 99%

“…Thus local density fluctuations are essential for the investigation of thermoacoustic oscillations. In combination with other techniques (e.g., chemiluminescence) the influence of direct and indirect noise can be discussed (Greiffenhagen et al 2019; Leitgeb et al 2013).…”

Section: Introductionmentioning

confidence: 99%

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Quantitative measurement of density fluctuations with a full-field laser interferometric vibrometer

et al. 2019

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Modern, lean and premixed gas turbine combustion concepts for low NOx emissions are prone to combustion instabilities. In a previous work it was shown that laser interferometric vibrometry (LIV) can be used to record global as well as local heat release fluctuations in swirl-stabilized premixed methane flames quantitatively, if other effects influencing density are small. In this work a newly developed camera-based full-field LIV system (CLIV) was applied to a lean, confined, premixed and swirl-stabilized methane flame under atmospheric conditions. Instead of time-consuming pointwise scanning of the flame, CLIV records full-field line-of-sight density fluctuations with high spatio-temporal resolution. With a recording rate of 200 kHz, CLIV enables the visualization of highly unsteady processes in fluid dynamics and combustion research. As an example for an unsteady process, the propagation of the flame front through a lean, premixed gas volume is visualized during an ignition process. A discussion of algorithms and assumptions necessary to calculate heat release oscillations from density oscillations is presented and applied to phase-averaged data recorded with CLIV for this type of flame. As reference, OH* chemiluminescence data were recorded simultaneously. While density gradients travelling with the flow are recorded by LIV and CLIV, chemiluminescence imaging will show nothing in the absence of chemical reaction.Graphic abstracta Time-averaged density gradient within the combustor in lateral direction. b Density fluctuations along line-of-sight 7 ms after ignition. c Phase-averaged and local heat release fluctuations at 225 Hz perturbation frequency

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Quantitative measurement of density fluctuations with a full-field laser interferometric vibrometer

et al. 2019

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Heterodyne background-oriented schlieren for the measurement of thermoacoustic oscillations in flames

Tasmany,

Kaiser,

Woisetschläger

et al. 2024

Exp Fluids

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In aircraft engines, thermoacoustic oscillations in the combustion chamber contribute significantly to noise emissions, which, like all other emissions, must be drastically reduced. Thermoacoustic oscillations are not only a concern, they can also be beneficial in hydrogen combustion. This work demonstrates that thermoacoustic density oscillations with amplitudes at least an order of magnitude smaller than those resulting from density gradients in a turbulent flame can be detected using laser interferometric vibrometry. This improvement was made possible by heterodyning a carrier fringe system in background-oriented schlieren (BOS) recordings, which were subsequently analyzed using techniques commonly used for holographic interferometry. In comparison with other BOS evaluation techniques, the filtering of the individual frames in the Fourier domain offers a more efficient computational approach, as it allows for phase averaging of a high number of single recordings to reduce noise from turbulence. To address fringe pattern distortions and cross talk in the Fourier domain, which both have been observed by other authors, we propose background subtraction methods and an optimized background pattern. Additionally, the procedure provides a visualization tool for marking the high turbulence regions of heat release by the variations in fringe amplitude. Finally, the line-of-sight data are reconstructed using the inverse Abel transform, with the data calibrated by laser interferometric techniques, resulting in local values for density oscillations. Graphical abstract

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Laser interferometric detection of heat release rate perturbation field of acoustically perturbed laminar premixed flames

Liang,

Yang,

Zhang

et al. 2024

Experimental Thermal and Fluid Science

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Discussion of laser interferometric vibrometry for the determination of heat release fluctuations in an unconfined swirl-stabilized flame

Cited by 8 publications

References 26 publications

Quantitative measurement of density fluctuations with a full-field laser interferometric vibrometer

Quantitative measurement of density fluctuations with a full-field laser interferometric vibrometer

Heterodyne background-oriented schlieren for the measurement of thermoacoustic oscillations in flames

Laser interferometric detection of heat release rate perturbation field of acoustically perturbed laminar premixed flames

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