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Research Papers

Mechanisms for Wide-Chord Fan Blade Flutter

[+] Author and Article Information
Mehdi Vahdati

 Imperial College London MED, Exhibition Road, London SW7 2AZ, UKm.vahdati@imperial.ac.uk

George Simpson

 Rolls-Royce PLC, P.O. Box 31, Derby DE24 8BJ, UK

Mehmet Imregun

 Imperial College London MED, Exhibition Road, London SW7 2AZ, UK

J. Turbomach 133(4), 041029 (Apr 27, 2011) (7 pages) doi:10.1115/1.4001233 History: Received August 19, 2009; Revised October 28, 2009; Published April 27, 2011; Online April 27, 2011

This paper describes a detailed wide-chord fan blade flutter analysis with emphasis on flutter bite. The same fan was used with three different intakes of increasing complexity to explain flutter mechanisms. Two types of flutter, namely, stall and acoustic flutters, were identified. The first intake is a uniform cylinder, in which there are no acoustic reflections. Only the stall flutter, which is driven by flow separation, can exist in this case. The second intake, based on the first one, has a “bump” feature to reflect the fan’s forward pressure wave at a known location so that detailed parametric studies can be undertaken. The analysis revealed a mechanism for acoustic flutter, which is driven by the phase of the reflected wave. The third intake has the typical geometric features of a flight intake. The results indicate that flutter bite occurs when both stall and acoustic flutters happen at the same speed. It is also found that blade stiffening has no effect on aero-acoustic flutter.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Computational domain

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Figure 2

Computed characteristic

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Figure 3

1F/2ND assembly vibration mode

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Figure 16

Aerodamping as a function of the blade frequency—plain intake

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Figure 17

Aerodamping as a function of blade frequency—80% speed, flight intake

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Figure 4

Aerodamping with plain intake

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Figure 5

Steady-state pressure and stall regions on suction surface (S/S)

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Figure 6

Unsteady pressure amplitude on the blade surface (left) and time histories at points A and B (dx: motion, dp: pressure)

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Figure 7

Aerodamping as a function of the bump position

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Figure 8

Displacement and modal force time histories for X1 and X2

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Figure 9

Unsteady pressure waves: (a) unsteady pressure, (b) forward pressure wave, and (c) backward pressure wave

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Figure 10

(a) Total aerodamping (left) and (b) aerodamping due to bump only

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Figure 11

Domain used for flutter analysis—real intake

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Figure 12

Characteristic computed with flight intake

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Figure 13

Aerodamping along high working line HWK

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Figure 14

1D forward and backward waves (104 Pa)

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Figure 15

(a) Amplitude and (b) phase of the reflected wave

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