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

Felix Greiffenhagen, Jakob Woisetschläger, Johannes Gürtler, Jürgen Czarske

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Abstract

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 onditions. 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.
Original languageEnglish
Number of pages15
JournalExperiments in fluids
Volume2020
Issue number61:9
DOIs
Publication statusE-pub ahead of print - 28 Nov 2019

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Fields of Expertise

  • Mobility & Production

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