0
Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Mapping the Density Fluctuations in a Pulsed Air-Methane Flame Using Laser-Vibrometry

[+] Author and Article Information
Fabrice Giuliani1

Department for Gas Turbine Combustion, Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, Inffeldgasse 25A, A-8010 Graz, Austriafabrice.giuliani@tugraz.at

Thomas Leitgeb, Andreas Lang, Jakob Woisetschläger

Department for Gas Turbine Combustion, Institute for Thermal Turbomachinery and Machine Dynamics, Graz University of Technology, Inffeldgasse 25A, A-8010 Graz, Austria

1

Corresponding author.

J. Eng. Gas Turbines Power 132(3), 031603 (Dec 03, 2009) (8 pages) doi:10.1115/1.3159373 History: Received March 23, 2009; Revised March 26, 2009; Published December 03, 2009; Online December 03, 2009

Laser vibrometry (LV) is originally a laser-based, line-of-sight measurement technique dedicated to the analysis of surface vibrations. It was lately adapted at TU Graz for monitoring the stability of an air-methane flame (Giuliani, , 2006, ASME Turbo Expo, ASME Paper No. GT2006-90413). This paper reports on the mapping of density fluctuations measured with LV in a premixed air-methane flame (free jet; swirl stabilized) with a forced flow modulation (quarter-wave resonator; amplification with a siren). In order to correlate the density fluctuations with the jet aerodynamics and turbulent flame shape, stereoscopic particle image velocimetry and high-speed schlieren visualizations were used. This paper addresses issues regarding the estimate of density fluctuations, the transform from line-of-sight to local measurement with tomographic methods, and the potential of the method for detailed description of thermoacoustic couplings. One emphasized application of LV is its ability to perform precise and low-cost benchmark stability tests on a combustor during the design phase (time-resolved measurement, high frequency and phase resolution on the 5 Hz–20 kHz range with the present equipment and settings, near-constant spectral sensitivity over a large bandwidth, and no seeding required; measurement possible over the whole combustion volume).

FIGURES IN THIS ARTICLE
<>
Copyright © 2010 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

Test rig. Top: ensemble siren, resonator and burner. Middle: measurements performed on the free-jet flame per specific technique. Bottom: flame aspect during the PIV measurements.

Grahic Jump Location
Figure 2

ONERA siren, where a sonic jet sheared by a cogged wheel rotating at controlled velocity sets an air flow modulation at the desired frequency (12)

Grahic Jump Location
Figure 3

Principle of laser vibrometry and dual-LV arrangement

Grahic Jump Location
Figure 4

Comparison between the LV output signal related to the time derivative of the density—or flat response, and the density itself—or 1/f response (the LV processor has an embedded integrator). Excitation at 540 Hz

Grahic Jump Location
Figure 5

Phase averaging process for LV signals, over a 25 Hz pulsation. Top: time signals. Bottom: phase-averaged signals displayed over four pulsation cycles, with the scanning LV voltage uf′, and resulting ρf′ computed after Eq. 2.

Grahic Jump Location
Figure 6

Fluctuating density mapping process. The measurement grid is displayed in Fig. 1. (a) Map of the scanning LV filtered voltage uf′(t) at frequency f=175 Hz and (b) phase subperiod t=dτ. (c) Map of the relative density fluctuation ρfLS′(t). (d) Abel transform of the latter. Light contours: negative part of the fluctuation, line contours: positive part.

Grahic Jump Location
Figure 7

Stereo-PIV arrangement and measurement plane

Grahic Jump Location
Figure 8

Recurrent mushroom-shaped flame observed with schlieren technique. The field of view is defined in Fig. 1. Siren pulsation frequency 175 Hz. Four phase-locked subperiodes are displayed with incremental time step τ/6=1.9 m s from top to bottom.

Grahic Jump Location
Figure 9

Pulsed jet description at isothermal conditions. The measurement plane is defined in Figs.  17. Siren pulsation frequency 175 Hz. Vectors: PIV measurements in the jet median plane. Contour plots represent the vorticity (unit is 2π rad/s). Filled contours: anticlockwise rotation. Line contours: clockwise motion.

Grahic Jump Location
Figure 10

Pulsed flame periphery description. The measurement plane is defined in Figs.  17. Siren pulsation frequency 175 Hz. Vectors: PIV measurements in the flame median plane. Filled contours: anticlockwise rotation. Line contours: clockwise rotation. The plots are synchronous with the ones from Fig. 8.

Grahic Jump Location
Figure 11

Density fluctuation maps covering one pulsation cycle, based on phase-averaged LV signals, performed on a pulsed flame (free jet, 175 Hz). Relative density fluctuation ρfLS′(dτ) (line-of-sight, computed with Eq. 2). Filled contours: positive ρ values. Line contours: negative ρ values. Contour color: amplitude of density fluctuation |ρ′|. The plots are synchronous with the ones from Figs.  810.

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In