Analysis of flow and density oscillations in a swirl-stabilized flame employing highly resolving optical measurement techniques

Fischer, Andreas; König, Jörg; Czarske, Jürgen; Peterleithner, Johannes; Woisetschläger, Jakob; Leitgeb, Thomas

doi:10.1007/s00348-013-1622-3

Cited by 11 publications

(4 citation statements)

References 27 publications

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“…Furthermore, the absolute value in the spectrum decreases with increasing frequency. This is typical for flow turbulence indicating the decay of the vortices according to Kolmogorov's theory and is different from the white noise due to the measurement uncertainty (Fischer et al, 2013a). For frequencies over 3 kHz the spectrum converges towards a constant value mean(|FFT(v)| 2 ) = σ/ √ 900 000 = 1.5 mm s −1 , which is a measure of the velocity standard deviation after averaging over 900 000 samples, i.e.…”

Section: Characterization Measurementmentioning

confidence: 93%

High-speed camera-based measurement system for aeroacoustic investigations

Gürtler

Haufe

Schulz

et al. 2016

J. Sens. Sens. Syst.

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Abstract. The interaction of sound and flow enables an efficient noise damping. Inevitable for understanding of this aeroacoustic damping phenomenon is the simultaneous measurement of flow and sound fields. Optical sensor systems have the advantage of non-contact measurements. The necessary simultaneous determination of sound levels and flow velocities with high dynamic range has major hurdles. We present an approach based on frequency-modulated Doppler global velocimetry, where a high-speed CMOS camera with data rates over 160 MSamples s −1 of velocity samples is employed. Using the proposed system, two-component flow velocity measurements are performed in a three-dimensional region of interest with a spatial resolution of 224 µm, based on single-pixel evaluation, and a measurement rate of 10 kHz. The sensor system can simultaneously capture sound and turbulent flow velocity oscillations down to a minimal power density of 40.5 (mm s −1 ) 2 Hz −1 in a frequency range up to 5 kHz. The presented measurements of the interaction of sound and flow support the hypothesis that the sound energy is transferred into flow energy.

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Section: Characterization Measurementmentioning

confidence: 93%

High-speed camera-based measurement system for aeroacoustic investigations

Gürtler

Haufe

Schulz

et al. 2016

J. Sens. Sens. Syst.

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“…A more recent experimental approach is the recording of density fluctuations with laser interferometric vibrometry (LIV) in unconfined (Giuliani et al 2006; Leitgeb et al 2013; Fischer et al 2013) as well as in confined flames (Peterleithner et al 2016). Such commercially available LIV systems were originally designed to record surface vibrations but can also be used to detect integral changes of the refractive index along the laser beam.…”

Section: Introductionmentioning

confidence: 99%

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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“…The single observation direction perpendicular to the window of the combustion chamber minimizes the errors due to image distortions. Furthermore, Fischer et al reported time-resolved DGV measurements with a measurement rate of 100 kHz to investigate flow velocity oscillations and thermoacoustic phenomena [188,189]. High-speed PIV measurements with rates up to 10 kHz were achieved by Boxx et al [119,190], whereas volumetric, single shot PIV measurements in flames were for instance reported by Tokarev et al [191].…”

Section: Application Examples Challenges and Perspectivesmentioning

confidence: 99%

Imaging Flow Velocimetry with Laser Mie Scattering

Fischer

2017

Applied Sciences

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Abstract:Imaging flow velocity measurements are essential for the investigation of unsteady complex flow phenomena, e.g., in turbomachines, injectors and combustors. The direct optical measurement on fluid molecules is possible with laser Rayleigh scattering and the Doppler effect. However, the small scattering cross-section results in a low signal to noise ratio, which hinders time-resolved measurements of the flow field. For this reason, the signal to noise ratio is increased by using laser Mie scattering on micrometer-sized particles that follow the flow with negligible slip. Finally, the ongoing development of powerful lasers and fast, sensitive cameras has boosted the performance of several imaging methods for flow velocimetry. The article describes the different flow measurement principles, as well as the fundamental physical measurement limits. Furthermore, the evolution to an imaging technique is outlined for each measurement principle by reviewing recent advances and applications. As a result, the progress, the challenges and the perspectives for high-speed imaging flow velocimetry are considered.

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Analysis of flow and density oscillations in a swirl-stabilized flame employing highly resolving optical measurement techniques

Cited by 11 publications

References 27 publications

High-speed camera-based measurement system for aeroacoustic investigations

High-speed camera-based measurement system for aeroacoustic investigations

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

Imaging Flow Velocimetry with Laser Mie Scattering

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