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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Acoustoelastic Interaction in Combustion Chambers: Modeling and Experiments

[+] Author and Article Information
R. A. Huls1

Faculty of Engineering Technology, Section of Applied Mechanics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands

J. F. van Kampen, J. B. Kok

Faculty of Engineering Technology, Section of Thermal Engineering, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands

P. J. van der Hoogt, A. de Boer

Faculty of Engineering Technology, Section of Applied Mechanics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands

Because the boundary conditions of the combustion chamber are not zero velocity at the ends due to the plenum and the water cooler, not exactly one half wave fits in.

The correlated part is determined as $S11=S12S21∕S22$, in which $S22$ denotes an autospectrum and $S12$ denotes a cross spectrum (32).

1

Corresponding author.

J. Eng. Gas Turbines Power 130(5), 051505 (Jun 16, 2008) (8 pages) doi:10.1115/1.2938391 History: Received March 06, 2007; Revised March 04, 2008; Published June 16, 2008

Abstract

To decrease $NOx$ emissions from combustion systems, lean premixed combustion is used. A disadvantage is the higher sensitivity to combustion instabilities, leading to increased sound pressure levels in the combustor and resulting in an increased excitation of the surrounding structure: the liner. This causes fatigue, which limits the lifetime of the combustor. This paper presents a joint experimental and numerical investigation of this acoustoelastic interaction problem for frequencies up to $1kHz$. To study this problem experimentally, a test setup has been built consisting of a single burner, $500kW$, $5bar$ combustion system. The thin structure (liner) is contained in a thick pressure vessel with optical access for a traversing laser vibrometer system to measure the vibration levels of the liner. The acoustic excitation of the liner is measured using pressure sensors measuring the acoustic pressures inside the combustion chamber. For the numerical model, the finite element method with full coupling between structural vibration and acoustics is used. The flame is modeled as an acoustic volume source corresponding to a heat release rate that is frequency independent. The temperature distribution is taken from a Reynolds averaged Navier Stokes (RaNS) computational fluid dynamics (CFD) simulation. Results show very good agreement between predicted and measured acoustic pressure levels. The predicted and measured vibration levels also match fairly well.

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Figures

Figure 1

Cross section of the test rig: 1=plenum, 2=burner, 3=combustion chamber, 4=windows, 5=liner, 6=pressure vessel, 7=thin liner part, and 8=exit tube

Figure 2

Mesh of the acoustoelastic finite element model

Figure 3

Cross section of the temperature field in the combustion chamber from CFD used in the FEM model (°C)

Figure 4

Temperature dependence of Young’s modulus E. (—) typical stainless steel, (×) stainless steel 310, and (○) Hastelloy X.

Figure 5

Construction for liner temperature measurement (left) and the temperature measured (right). (—) before the flexible section and (– –) after the flexible section.

Figure 6

Calculated (black) and measured (gray) autospectra for sensor p2 (combustion chamber) with flame noise excitation. The dashed lines denote calculated acoustic eigenfrequencies.

Figure 7

Different structural mode shapes of the (11) mode

Figure 8

Shape of the liner in the structural section; gases flow from left to right

Figure 9

Amplitude (top) and phase with respect to pressure sensor p3 (bottom) of the mode shapes measured during combustion

Figure 10

Measured and calculated autospectra of the mean vibration of the liner; gray is the part correlated with p3. The dashed lines denote acoustic eigenfrequencies and the dotted lines denote structural eigenfrequencies.

Figure 11

Calculated autospectrum of the mean vibration of the liner for an asymmetric structure

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