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Gas Turbines: Combustion, Fuels, and Emissions

Considerations on the Numerical Modeling and Performance of Axial Swirlers Under Relight Conditions

[+] Author and Article Information
Nicholas Grech1

Charlie Koupper, Pavlos K. Zachos, Vassilios Pachidis, Riti Singh

Department of Power and Propulsion,  Cranfield University, Bedfordshire, MK43 0AL, United Kingdom

1

Corresponding author.

J. Eng. Gas Turbines Power 134(11), 111505 (Sep 28, 2012) (8 pages) doi:10.1115/1.4007132 History: Received June 26, 2012; Revised July 10, 2012; Published September 28, 2012; Online September 28, 2012

Numerical modeling of aero engine combustors under relight conditions is a matter of continuously increasing importance due to the demanding engine certification regulations. In order to reduce the complexity and the cost of the numerical modeling, common practice is to replace the atomizer’s swirlers with velocity profiles boundary conditions, very often scaled down from nominal operating conditions assuming similarity of the swirler flowfield. The current numerical study focuses on the flowfield characteristics of an axially swirled atomizer operating within a windmilling engine environment. The scalability of the velocity profile from higher power settings is examined. Observations on the performance of the axial swirler under relight conditions are also made. Experimental data was used as a validation platform for the numerical solver, after a grid sensitivity study and a turbulence model selection process. Boundary conditions for simulating the windmilling environment were extracted from experimental work. The swirler axial and tangential velocity profiles were normalized using the swirler inlet velocity. Results showed that both profiles are only scalable for windmilling conditions of high flight Mach number ( 0.5). At low flight Mach numbers, the actual profile had a lower velocity than that predicted through scaling. The swirl number was found to deteriorate significantly with the flight velocity following a linear trend, reducing significantly the expected flame quality. As a consequence the burner is forced to operate at the edge of its stability loop with low certainty regarding its successful relight.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Effect of swirl number on the flame front [14]

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Figure 2

Swirler dimensions (mm)

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Figure 3

Hex-core unstructured mesh

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Figure 4

Grid independency study

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Figure 5

Predicted recirculation zone boundary

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Figure 6

Total and static pressure losses

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Figure 7

Normalized velocity profiles

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Figure 8

Swirl number deterioration

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Figure 9

Numerical versus experimental profiles: flat and curved vanes

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Figure 10

Windmilling boundary conditions

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Figure 11

Axial velocity along swirler axis

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Figure 12

Subidle velocity profiles

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Figure 13

Normalized axial velocity along swirler axis

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Figure 14

Vane Reynolds number

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Figure 15

Swirl number for subidle conditions

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Figure 16

Swirl number correlation for subidle conditions

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