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

The Influence of Dump Gap on External Combustor Aerodynamics at High Fuel Injector Flow Rates

[+] Author and Article Information
A. Duncan Walker, James J. McGuirk

Department of Aeronautical and Automative Engineering, Loughborough University, Loughborough LE11 3TU, UK

Jon F. Carrotte

Department of Aeronautical and Automative Engineering, Loughborough University, Loughborough LE11 3TU, UKj.f.carrotte@lboro.ac.uk

J. Eng. Gas Turbines Power 131(3), 031506 (Feb 11, 2009) (10 pages) doi:10.1115/1.3028230 History: Received April 21, 2008; Revised May 08, 2008; Published February 11, 2009

The increasing demand to reduce fuel burn, hence CO2 emissions, from the gas turbine requires efficient diffusion to reduce the system pressure loss in the combustor. However, interactions between prediffuser and combustor can have a significant effect on diffuser performance. For example, the consequence of increased fuel injector flow at a dump gap set using conventional design guidelines has been shown (Walker, A. D., Carrotte, J. F., and McGuirk, J. J., 2007. “Compressor∕Diffuser∕Combustor Aerodynamic Interactions in Lean Module Combustors  ,” ASME Turbo Expo 2007—Power for Land Sea and Air, Paper No. GT2007-27872) to introduce a destabilizing interaction between fuel injector and upstream components. The present paper concentrates on examining the effects of increased dump gap. Dump gap ratios of 0.8, 1.2, and 1.6 were employed, with each test utilizing the same inlet guide vane, compressor rotor, integrated outlet guide vane (OGV)∕prediffuser, and dump geometry. The flow fraction of compressor efflux entering the combustor cowl was set to be representative of lean combustors (50–70%). Measurements were made on a fully annular rig using a generic flame tube with metered cowl and inner∕outer annulus flows. The results demonstrate that, with fixed cowl flow, as the dump gap increases, component interactions decrease. At a dump gap ratio of 0.8, the proximity of the flame tube influences the prediffuser providing a beneficial blockage effect. However, if increased to 1.2, this beneficial effect is weakened and the prediffuser flow deteriorates. With further increase to 1.6, the prediffuser shows strong evidence of separation. Hence, at the dump gaps probably required for lean module injectors, it is unlikely the prediffuser will be influenced beneficially by the flame tube blockage; this must be taken into account in the design. Furthermore, with small dump gaps and high cowl flow fraction, the circumferential variation in cowl flow can feed upstream and cause OGV∕rotor forcing. At larger dump gaps, the circumferential variation does not penetrate upstream to the OGV, and the rotor is unaffected. The optimum dump gap and prediffuser design for best overall aerodynamic system performance from rotor through to feed annuli is a compromise between taking maximum advantage of upstream blockage effects and minimizing any 3D upstream forcing.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Geometrical notation

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Figure 3

Measurement planes

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Figure 4

Combustor details

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Figure 5

Axial velocity contours at prediffuser exit (X4) (height 65.9mm, sector angle Δθ=18deg, 8-OGV passages)

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Figure 6

Pitch average static pressure at prediffuser exit (X4), fixed dump (d∕hX4), varying flow

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Figure 7

Pitch averaged profiles at prediffuser exit (X4) injector mass flow, mcowl=70%

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Figure 8

Static pressure contorus at prediffuser exit (X4), (height 65.9mm, sector angle Δθ=18deg, 8-OGV passages)

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Figure 9

Dump static pressure (on line L-L in Fig. 3)

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Figure 10

Axial velocity contours at OGV exit (X3) (height=36.6mm, sector angle Δθ=4.5deg, 2-OGV passages)

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Figure 11

OGV exit (reference) total pressure

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Figure 12

rotor exit static pressure (mcowl=70%)

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Figure 13

Pitch averaged profile at rotor exit (X2) cowl mass, flow, mcowl=70%

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Figure 14

Axial velocity contours in inner annulus (X5i) (sector angle Δθ=18deg)

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Figure 15

Axial velocity contours in outer annulus (X5o) (sector angle Δθ=18deg)

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Figure 16

Loss contours in the feed annuli (X5) (d∕hX4=1.6, mcowl=70%, sector angle Δθ=18deg)

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