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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuel

# Laser-Based Investigations of Thermoacoustic Instabilities in a Lean Premixed Gas Turbine Model Combustor

[+] Author and Article Information
Peter Weigand

Institute of Combustion Technology, German Aerospace Center (DLR), Pfaffenwaldring 38-40, 70565 Stuttgart, Germanypeter.weigand@dlr.de

Wolfgang Meier, Manfred Aigner

Institute of Combustion Technology, German Aerospace Center (DLR), Pfaffenwaldring 38-40, 70565 Stuttgart, Germany

Xuru Duan1

Institute of Combustion Technology, German Aerospace Center (DLR), Pfaffenwaldring 38-40, 70565 Stuttgart, Germany

1

Present address: Southwestern Institute of Physics, P.O. Box 432 Chengdu Sichuan 610041, China

J. Eng. Gas Turbines Power 129(3), 664-671 (Oct 16, 2006) (8 pages) doi:10.1115/1.2718224 History: Received June 09, 2006; Revised October 16, 2006

## Abstract

Nonintrusive laser-based and optical measurements were performed in a gas turbine model combustor with a lean premixed swirl-stabilized $CH4$-air flame at atmospheric pressure. The main objective was to gain spatially and temporally resolved experimental data to enable the validation of numerical CFD results of oscillating flames. The investigated flame was operated at 25 kW and ϕ=0.70, and exhibited self-excited oscillations of more than 135 dB at $≈300Hz$. The applied measurement techniques were three-dimensional (3D) laser doppler velocimetry (LDV) for velocity measurements, $OH*$ chemiluminescence yielding information about the heat release and pointwise laser Raman scattering for the determination of joint probability density functions (PDFs) of the major species concentrations, temperature, and mixture fraction. Each of these techniques was applied with phase resolution with respect to the periodic fluctuation of the pressure in the combustion chamber that was measured with a microphone probe. The measurements finally revealed that the mixing of fuel and air in this technical premixing system was strongly affected by the pressure fluctuations leading to changes in equivalence ratio during an oscillation cycle that, in turn, induced the pressure fluctuations.

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## Figures

Figure 1

Schematic of the injector with combustion chamber and photo of the flame

Figure 2

Time log of the pressure signals and respective spectra from the plenum and the combustion chamber

Figure 3

Pressure signal of the plenum with trigger scheme for the pulsed measurements

Figure 4

Pressure oscillation compared to a pure sine function; the dark (black) curve shows a sine function and the light (red) curve displays the pressure signal of the plenum. The markers ph1–ph8 indicate the assigned phase angles at which measurements were performed. These were ph1=0deg, ph2=50deg, ph3=105deg, ph4=150deg, ph5=195deg, ph6=230deg, ph7=270deg, and ph8=315deg.

Figure 5

Vector plot of the mean uv velocities; the half profiles were mirrored to yield a more complete impression of the flow; zones with negative and positive u velocities are marked dark red and light blue, respectively. The coloring is based on interpolation of the measured mean u velocities (using the program Tecplot 10).

Figure 6

Contours of u=0m∕s for different phase angles indicating the changes of the inner recirculation zone during a pressure cycle (values mirrored for better visualization)

Figure 7

Radial profiles of axial velocity (top) and circumferential velocity (bottom) for different phase angles at h=5mm

Figure 8

Deconvoluted OH* chemiluminescence images (averaged over 200 images) for different phases; the sharp gradients and the extremely high intensities at the walls are an artifact of the deconvolution routine, but there are, in reality, high intensities near the walls at ph3 (in particular from ph2 to ph4 and still at ph5)

Figure 9

Normalized integrated OH* chemiluminescence and normalized pressure fluctuation in the combustion chamber

Figure 10

2D temperature distribution from interpolation (using the program ORIGIN 7.5) of single-point Raman measurements (averaged over 400 sample at each position) at the heights h=6mm, 15mm, 25mm, 35mm, and 60mm for different phase angles. The measurement positions are indicated by stars at ph1.

Figure 11

2D distribution of CH4 volume fraction interpolated from single-point Raman measurements (using the program ORIGIN 7.5), combined with the uv vectors of the LDA measurements for different phase angles

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