Research Papers: Gas Turbines: Structures and Dynamics

Optical Methods for Studies of Self-Excited Oscillations and the Effect of Dampers in a High Pressure Single Sector Combustor

[+] Author and Article Information
U. Meier, L. Lange, J. Heinze, C. Hassa

DLR–German Aerospace Center,
Institute of Propulsion Technology,
Linder Hoehe,
Cologne D-51147, Germany

S. Sadig

Rolls-Royce Deutschland Ltd & Co KG,
Eschenweg 11, Dahlewitz,
Blankenfelde-Mahlow 15827, Germany

D. Luff

Rolls-Royce plc UK,
Derby DE24 8BJ, UK

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 12, 2014; final manuscript received November 27, 2014; published online January 21, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(7), 072505 (Jul 01, 2015) (9 pages) Paper No: GTP-14-1483; doi: 10.1115/1.4029355 History: Received August 12, 2014; Revised November 27, 2014; Online January 21, 2015

Self-excited periodic instabilities in a staged lean burn injector could be forced by operating the combustor at off-design conditions. These pressure oscillations were studied in a high pressure single sector combustor with optical access. Two damper configurations were installed and tested with respect to their damping efficiency in relation to the configuration without dampers. For a variety of test conditions, derived from a part load case, time traces of pressure in the combustor were measured, and amplitudes were derived from their Fourier transformation. These measurements were performed for several combinations of the operating parameters, i.e., injector pressure drop, air/fuel ratio (AFR), pilot/main fuel split, and preheat temperature. These tests “ranked” the respective damper configurations and their individual efficiency with respect to the configuration without dampers. Although a general trend could be observed, the ranking was not strictly consistent for all operating conditions. For several test cases, preferably with pronounced self-excited pressure oscillations, phase-resolved planar optical measurement techniques were applied to investigate the change of spatial structures of fuel, reaction zones, and temperature distributions over a period of an oscillation. A pulsating motion was detected for both pilot and main flame, driven by a pulsating transport of the liquid fuel. This pulsation, in turn, is caused by a fluctuating air velocity, in connection with a prefilming airblast type atomizer. A phase shift between pilot and main injector heat release was observed, corresponding to a shift of fuel penetration. Local Rayleigh indices were calculated qualitatively, based on phase-resolved OH chemiluminescence used as marker for heat release, and corresponding pressure values. This identified regions, where a local amplification of pressure oscillations occurred. These regions were largely identical to the reaction regions of pilot and main injector, whereas the recirculation zone between the injector flows was found to exhibit a damping effect.

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Fig. 1

Test section BOSS during operation and schematic

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Fig. 2

Downstream view from plenum toward injector. Top: standard injector mount with perforated plate; bottom: open injector support structure.

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Fig. 3

Rolls-Royce lean burn fuel injector with concentric arrangement; pilot injector at center. (a) Main fuel flow; (b) pilot fuel flow; (c) pilot air flow; and (d) main air flow. Left: schematics; right: operation in BOSS rig.

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Fig. 4

Comparison of damping characteristic of narrowband and broadband damper

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Fig. 5

Optical arrangement—1: camera (OH and kerosene LIF); 2: camera (Mie or kerosene LIF); 3: photomultiplier (OH*); 4: reference cells; 5: camera (reference cell); 6: light sheet optics; 7: laser (Nd:YAG); 8: laser (dye); 9: frequency doubling; 10: pressure sensors combustor; 11: pressure sensor plenum; 12: 4-channel A/D converter and storage.

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Fig. 6

Relative pressure amplitudes with and without damper for test conditions listed in Table 1

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Fig. 7

Heat release distribution of pilot and main stage over one period for test case 3, no damper

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Fig. 8

Integral heat release of pilot and main injector as function of phase angle

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Fig. 9

Fourier spectrum of the combustor pressure transducer signal for test case 3

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Fig. 10

Distributions of temperature (top), heat release (center), and liquid fuel (bottom) for test case 4 with narrowband damper

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Fig. 11

Distributions of temperature (top), heat release (center), and liquid fuel (bottom) for test case 5 with narrowband damper for 8 phase intervals at reduced pilot fuel split

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Fig. 12

Distribution of liquid (top row) and both liquid and evaporated kerosene (bottom row) in a central plane though the injector axis. Left to right: pos. zero crossing, maximum; neg. zero crossing, minimum of combustor pressure. Test condition as in Fig. 11 (case 5).

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Fig. 13

Spatial distribution of Rayleigh indices for three different configurations at test case 3. False color images show product of Abel-transformed OH chemiluminescence and corresponding combustor pressure.

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Fig. 14

Rayleigh indices for test case 3, no damper, in relation to flow field

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Fig. 15

Effect of pilot fuel split on spatial distributions of Rayleigh indices (a) and OH chemiluminescence (b). No damper installed. Left test case 3 (lower pilot fuel split), right test case 2 (higher pilot fuel split).




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