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

Air Flow Modulation for Refined Control of the Combustion Dynamics Using a Novel Actuator

[+] Author and Article Information
Fabrice Giuliani1

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

Andreas Lang, Klaus Johannes Gradl, Peter Siebenhofer, Johannes Fritzer

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

1

Corresponding author.

J. Eng. Gas Turbines Power 134(2), 021602 (Dec 07, 2011) (8 pages) doi:10.1115/1.4004147 History: Received April 12, 2011; Accepted April 17, 2011; Published December 07, 2011; Online December 07, 2011

A specific actuator able to modulate the air feed of a gas a burner at a given frequency and amplitude is presented. The Combustion Department at the Institute for Thermal Turbomachinery and Machine Dynamics at the Graz University of Technology has experience on the study of combustion instabilities in gas turbines using a flow excitor. The stability of an industrial burner is tested at elevated pressure and temperature conditions in the frame of the NEWAC project. For practical matters of operation among which the possibility to induce progressively a perturbation when the flame conditions are all set, the need was expressed to design, construct and validate a flexible actuator able to set an air flow modulation at a given frequency and at a desired amplitude level, with the possibility during operation to let these two factors vary in a given range independently from each other. This device should operate within the 0–1 kHz range and 0%–20% amplitude range at steady-state, during transients, or follow a specific time sequence. It should be robust and sustain elevated pressures. The objective is to bring a perturbation in the flow to which the combustor will respond, or not. For elevated levels of pulsation, it can simulate the presence of vortex-driven combustion instabilities. It can also act as a real-time actuator able to respond in frequency and in phase to actively damp a “natural” combustion instability. Other issues are a better and quicker mixing due to the enhanced turbulence level, and pushing forward the blow out limits at lean conditions with controlled injection dynamics. The basic construction is the one of a siren, with an elevated pressure side where the air is throttled, and a low pressure outlet where the resulting sonic jet is sheared by a rotating wheel. A mechanism allows to let vary the surface of interaction between the wheel and the jet. Two electromotors driven by Labview set both frequency and amplitude levels. This contribution describes the actuator’s principles, design, operation range and the results of the characterization campaign.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Principles of the TU Graz siren for modulation of air supply, with tunable frequency and amplitude

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Figure 2

Design of the siren. Top: sketch of the siren. Bottom: picture while mounted on the combustion test facility. Thermal protections and separate air-cooled casing for motor cooling are missing.

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Figure 3

Variation of amplitude of the pulsation, proportional to the blocked surface of the nozzle, as a function of the tilt angle set by the positioning motor

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Figure 4

Detail of the feedback sensor and increment wheel

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Figure 5

Time signals. Operation: Po  = 1.8 bar, m·=32g/s,f = 107 Hz, amplitude= 20%.

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Figure 6

Transient operation. Up: time signals. Bottom: 3D amplitude spectra as a function of time. Operation: Po  = 1.3 bar, m·=15g/s,f = 230 Hz down to 0 Hz with an approximate 3 Hz/s deceleration, amplitude= 20%.

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Figure 7

Amplitude modulation. Up: time signals. Bottom: 3D amplitude spectra as a function of time. Operation: Po  = 1.3 bar, m·=15g/s,f = 107 Hz, blockage = 20% start position stepwise down to approximately 10%.

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Figure 8

Batch sequence. Up: time signals. Bottom: 3D amplitude spectra as a function of time. Operation: Po  = 1.8 bar, m·=32g/s.

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Figure 9

Phase averaged LDA measurements for two excitation frequencies, at 30 and 452 Hz

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