Flow-flame interactions causing acoustically coupled heat release fluctuations in a thermo-acoustically unstable gas turbine model combustor

Journal Article · Tue Dec 14 23:00:00 EST 2010 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2010.07.011· OSTI ID:21390730

Steinberg, A M; Boxx, I; Stoehr, M; Meier, W ^[1]; Carter, C D ^[2]

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1. Institute for Combustion Technology, German Aerospace Centre (DLR), 70569 Stuttgart (Germany)
2. Air Force Research Laboratory, Wright-Patterson AFB, OH (United States)

A detailed analysis of the flow-flame interactions associated with acoustically coupled heat-release rate fluctuations was performed for a 10 kW, CH{sub 4}/air, swirl stabilized flame in a gas turbine model combustor exhibiting self-excited thermo-acoustic oscillations at 308 Hz. High-speed stereoscopic particle image velocimetry, OH planar laser induced fluorescence, and OH* chemiluminescence measurements were performed at a sustained repetition rate of 5 kHz, which was sufficient to resolve the relevant combustor dynamics. Using spatio-temporal proper orthogonal decomposition, it was found that the flow-field contained several simultaneous periodic motions: the reactant flux into the combustion chamber periodically oscillated at the thermo-acoustic frequency (308 Hz), a helical precessing vortex core (PVC) circumscribed the burner nozzle at 515 Hz, and the PVC underwent axial contraction and extension at the thermo-acoustic frequency. The global heat release rate fluctuated at the thermo-acoustic frequency, while the heat release centroid circumscribed the combustor at the difference between the thermo-acoustic and PVC frequencies. Hence, the three-dimensional location of the heat release fluctuations depended on the interaction of the PVC with the flame surface. This motivated the compilation of doubly phase resolved statistics based on the phase of both the acoustic and PVC cycles, which showed highly repeatable periodic flow-flame configurations. These include flames stabilized between the inflow and inner recirculation zone, large-scale flame wrap-up by the PVC, radial deflection of the inflow by the PVC, and combustion in the outer recirculation zones. Large oscillations in the flame surface area were observed at the thermo-accoustic frequency that significantly affected the total heat-release oscillations. By filtering the instantaneous reaction layers at different scales, the importance of the various flow-flame interactions affecting the flame area was determined. The greatest contributor was large-scale elongation of the reaction layers associated with the fluctuating reactant flow rate, which accounted for approximately 50% of the fluctuations. The remaining 50% was distributed between fine scale stochastic corrugation and large-scale corrugation due to the PVC. (author)

• OSTI ID: 21390730
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 12 Vol. 157; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AIR
BURNERS
COMBUSTION
COMBUSTION KINETICS
COMBUSTORS
CONTRACTION
ELONGATION
FLAMES
FLOW RATE
FLUCTUATIONS
GAS TURBINES
HZ RANGE
INSTABILITY
KHZ RANGE
LAYERS
METHANE
NOZZLES
OSCILLATIONS
PERIODICITY
POWER RANGE 01-10 KW
STOCHASTIC PROCESSES
Swirl-stabilized flames
TURBULENCE
Thermo-acoustic instabilities
Turbulence-flame interaction
VORTICES
ZONES