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TECHNICAL PAPERS

The Effect of Stagger Variability in Gas Turbine Fan Assemblies

[+] Author and Article Information
Mark J. Wilson, Mehmet Imregun

 Imperial College London, United Kingdom

Abdulnaser I. Sayma

 University of Sussex, Brighton, United Kingdom

J. Turbomach 129(2), 404-411 (Jun 06, 2006) (8 pages) doi:10.1115/1.2437776 History: Received May 25, 2006; Revised June 06, 2006

Fan blades of high bypass ratio gas turbine engines are subject to substantial aerodynamic and centrifugal loads, producing the well-known phenomenon of fan blade untwist. The accurate prediction of the running geometry, as opposed to the cold geometry at rest, is crucial in the assessment of aerodynamic performance, vibratory response, and noise production of the fan. The situation is further complicated by the fact that some geometric variation is inevitable even for the state-of-the-art manufacturing processes used. The aim of this paper is to investigate the effect of static stagger variability on the dynamic untwist behavior of fan assemblies. An aeroelastic model was used to show that under certain conditions the stagger pattern changes significantly, both in form and amplitude, relative to the static configuration. At other conditions, a strong correlation between the running and static patterns is demonstrated.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Untwist prediction method

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Figure 2

Projection of tip-gap mesh onto plane normal to tip stagger line at 7% chord: (a) before and (b) after a typical deformation

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Figure 3

Dominant low-frequency mode shapes: (a) first flap, (b) second flap, and (c) first torsion

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Figure 4

Schematic diagram of shock location for nominal blade near the tip: (a) unstarted, (b) intermediate, and (c) started flow

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Figure 5

Fan characteristics: ▴: CF-only with tip gap, ▵: CF+gas with tip gap, ●: CF-only without tip gap, 엯: CF+gas without tip gap, ∎: fine mesh CF-only without tip gap, and ◻: fine mesh CF+gas without tip gap

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Figure 6

Fan untwist: ▵: CF+gas with tip gap, 엯: CF+gas without tip gap, and ◻: fine mesh CF+gas without tip gap

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Figure 7

Fan-blade static pressure distributions on working line, CF-only without tip-gap, 91% height

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Figure 8

Fan-blade static pressure distributions on working line, CF+gas without tip-gap, 91% height

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Figure 9

Tip stagger relative to nominal blade, blade 1 misstaggered (+0.2deg): (a) unstarted, (b) intermediate, and (c) started

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Figure 10

Tip stagger relative to nominal blade, blade 1 misstaggered (−0.2deg): (a) unstarted, (b) intermediate, and (c) started

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Figure 11

Tip stagger relative to nominal blade, random misstagger: (a) unstarted, (b) intermediate, and (c) started

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Figure 12

Intermediate speed pressure untwist snapshots, blade 1 misstaggered (+0.2deg)

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Figure 13

Time evolution of flow parameters, normalized to CF-only steady-state, intermediate speed, blade 1 misstaggered (+0.2deg)

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Figure 14

Schematic diagram of shock structure on casing for equilibrium running geometry, no tip-gap, one blade misstaggered (+0.2deg)

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Figure 15

Nominal versus randomly misstaggered fan isentropic efficiency along working line; Mass flow and efficiency normalized relative to intermediate operating point

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Figure 16

Tip stagger relative to nominal blade, random misstagger, with and without tip gap

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