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Research Papers

Impact of an Upstream Film-Cooling Row on Mitigation of Secondary Combustion in a Fuel Rich Environment

[+] Author and Article Information
Brian T. Bohan

e-mail: Brian.Bohan@eglin.af.mil

David L. Blunck

e-mail: David.Blunck@wpafb.af.mil
Air Force Research Laboratory,
Wright-Patterson AFB, OH 45433

Marc D. Polanka

Air Force Institute of Technology,
Wright-Patterson AFB, OH 45433
e-mail: Marc.Polanka@afit.edu

Stanislav Kostka

e-mail: stanislavkostka@snet.net

Naibo Jiang

e-mail: Naibo.Jiang.ctr@wpafb.af.mil
Spectral Energies, LLC,
Dayton, OH 45431

Scott D. Stouffer

University of Dayton Research Institute,
Dayton, OH 45469
e-mail: Scott.Stouffer.ctr@wpafb.af.mil

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received April 17, 2013; final manuscript received April 22, 2013; published online September 26, 2013. Editor: David Wisler.

J. Turbomach 136(3), 031008 (Sep 26, 2013) (8 pages) Paper No: TURBO-13-1055; doi: 10.1115/1.4024690 History: Received April 17, 2013; Revised April 22, 2013

In advanced gas turbine engines that feature very short combustor sections, an issue of fuel-rich gases interacting with the downstream turbine components can exist. Specifically, in combustors with high fuel-to-air ratios, there are regions downstream of the primary combustion section that will require the use of film-cooling in the presence of incompletely reacted exhaust. Additional combustion reactions resulting from the combination of unburnt fuel and oxygen-rich cooling films can cause significant damage to the turbine. Research has been accomplished to understand this secondary reaction process. This experimental film-cooling study expands the previous investigations by attempting to reduce or mitigate the increase in heat flux that results from secondary combustion in the coolant film. Two different upstream cooling schemes were used to attempt to protect a downstream fan-shaped cooling row. The heat flux downstream was measured and compared between ejection with air compared to nitrogen in the form of a heat flux augmentation. Planar Laser Induced Fluorescence (PLIF) was used to measure relative OH concentration in the combustion zones to understand where the reactions occurred. A double row of staggered normal holes was unsuccessful at reducing the downstream heat load. The coolant separated from the surface generating a high mixing regime and allowed the hot unreacted gases to penetrate underneath the jets. Conversely, an upstream slot row was able to generate a spanwise film of coolant that buffered the reactive gases off the surface. Essentially no secondary reactions were observed aft of the shaped coolant hole ejection with the protective slot upstream. A slight increase in heat transfer was attributed to the elevated freestream temperature resulting from reactions above the slot coolant. Creating this full sheet of coolant will be a key toward future designs attempting to control secondary reactions in the turbine.

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Figures

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Fig. 1

Experimental arrangement

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Fig. 2

Film-cooling hole geometries (in centimeters)

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Fig. 3

Heat transfer gauge labels and positions

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Fig. 4

Configuration of the PLIF setup

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Fig. 5

Percent change in heat flux, Φ = 1.3 and 1.5, fan-shaped laidback holes, coolant = air/N2, Mf = variable

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Fig. 6

Percent change in heat flux as function of equivalence ratio

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Fig. 7

Percent change in heat flux, Φ = 1.3 and 1.5, US: offset normal, coolant = air, Mon = variable, DS: fan, coolant = air/N2, Mf = 2

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Fig. 8

PLIF OH concentration for Φ = 1.3 and M = 2; (a) left: offset: air, fan: air; (b) right: offset: N2, fan: air

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Fig. 9

Percent change in heat flux, Φ = 1.3 and 1.5, US: slot, coolant = air, Ms = variable, DS: fan, coolant = air/N2, Mf = 2

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Fig. 10

PLIF OH concentration for Φ = 1.5 and M = 2; (a) left: slot: air, fan: air; (b) right: slot: N2, fan: air

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