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

Sensitivity of Combustion Driven Structural Dynamics and Damage to Thermo-Acoustic Instability: Combustion-Acoustics-Vibration

[+] Author and Article Information
A. Can Altunlu

Mem. ASME
Section of Applied Mechanics,
Faculty of Engineering Technology,
University of Twente,
Enschede 7500 AE, Netherlands
e-mail: altunlua2@asme.org

Peter J. M. van der Hoogt, André de Boer

Section of Applied Mechanics,
Faculty of Engineering Technology,
University of Twente,
Enschede 7500 AE, Netherlands

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 14, 2013; final manuscript received June 15, 2013; published online January 2, 2014. Assoc. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 136(5), 051501 (Jan 02, 2014) (18 pages) Paper No: GTP-13-1009; doi: 10.1115/1.4025817 History: Received January 14, 2013; Revised June 15, 2013

The dynamic combustion process generates high amplitude pressure oscillations due to thermo-acoustic instabilities, which are excited within the gas turbine. The combustion instabilities have a significant destructive impact on the life of the liner material due to the high cyclic vibration amplitudes at elevated temperatures. This paper presents a methodology developed for mechanical integrity analysis relevant to gas turbine combustors and the results of an investigation of the combustion-acoustics-vibration interaction by means of structural dynamics. In this investigation, the combustion dynamics was found to be very sensitive to the thermal power of the system and the air-fuel ratio of the mixture fed into the combustor. The unstable combustion caused a dominant pressure peak at a characteristic frequency, which is the first acoustic eigenfrequency of the system. Besides, the higher-harmonics of this peak were generated over a wide frequency-band. The frequencies of the higher-harmonics were observed to be close to the structural eigenfrequencies of the system. The structural integrity of both the intact and damaged test specimens mounted on the combustor was monitored by vibration-based and thermal-based techniques during the combustion operation. The flexibility method was found to be accurate to detect, localize, and identify the damage. Furthermore, a temperature increase was observed around the damage due to hot gas leakage from the combustor that can induce detrimental thermal stresses enhancing the lifetime consumption.

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Figures

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Fig. 1

The feedback mechanism of the thermo-acoustic instabilities in combustion processes

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Fig. 2

The dimensions and the configuration of the aero-box

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Fig. 3

Experimental (above) and numerical (below) results for the mode shapes of the intact plate configuration

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Fig. 4

Sensitivity analysis on the eigenfrequencies

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Fig. 5

Damage sensitivity of mode shapes (top: intact and bottom: damaged)

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Fig. 6

Damage localization by the flexibility method

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Fig. 7

Combustor test system: (a) and (b) single, and (c) double liner configurations (upstream section (S1), flame-box (S2), and a rectangular liner (S3 and S4))

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Fig. 8

Combustor flame-box and wedge

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Fig. 9

Temperature dependence of the material properties

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Fig. 10

Flame-box assembly and specimen configuration

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Fig. 11

Laser surface scan on the damaged specimen mounted in the flame-box

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Fig. 12

Schematic representation of the structural condition monitoring system

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Fig. 13

Pressure spectrum of the combustor

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Fig. 14

Stability map for the double liner configuration

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Fig. 15

Liner surface temperature profile and flame profile for (a) case 12, stable, and (b) case 22, unstable

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Fig. 16

Mode shapes of the single liner configuration (top: experiment; bottom: FEM)

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Fig. 17

First two plate modes in the double liner configurations

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Fig. 18

Time signal and autospectrum of the acoustic pressure and velocity of the wall (case 22): (the measurement locations are shown in parentheses)

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Fig. 19

SPL inside the combustor

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Fig. 20

Velocity amplitude of the liner wall

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Fig. 21

SPL and the velocity amplitude of the liner wall

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Fig. 22

Measurement grid (9 × 9: υnode no.)

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Fig. 23

Cross-correlations of the pressure (at p7) and the velocity of the diagonal-nodes (υnode#) of the intact (left) and damaged (right) specimen

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Fig. 24

Laser zigzag path generation and nodal surface scanning grid and structural vibrations comparison

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Fig. 25

Structural response to instability peaks

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Fig. 26

Damage localization due to the change in the flexibility matrix

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Fig. 27

Temperature evolution on the intact (above) and damaged (below) specimens

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