0
Research Papers

Numerical Study on Aeroelastic Instability for a Low-Speed Fan

[+] Author and Article Information
Kuen-Bae Lee

Imperial College London,
Mechanical Engineering Department,
London SW7 2AZ, UK
e-mail: klee2@ic.ac.uk

Mark Wilson

Rolls-Royce plc,
Derby DE24 8BJ, UK
e-mail: mark.wilson@rolls-royce.com

Mehdi Vahdati

Imperial College London,
Mechanical Engineering Department,
London SW7 2AZ, UK
e-mail: m.vahdati@imperial.ac.uk

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received September 27, 2016; final manuscript received November 29, 2016; published online February 23, 2017. Editor: Kenneth Hall.

J. Turbomach 139(7), 071004 (Feb 23, 2017) (8 pages) Paper No: TURBO-16-1262; doi: 10.1115/1.4035569 History: Received September 27, 2016; Revised November 29, 2016

Over recent years, engine designs have moved increasingly toward low specific thrust cycles to deliver significant specific fuel consumption (SFC) improvements. Such fan blades may be more prone to aerodynamic and aeroelastic instabilities than conventional fan blades. The aim of this paper is to analyze the flutter stability of a low-speed/low pressure ratio fan blade. By using a validated computational fluid dynamics (CFD) model (AU3D), three-dimensional unsteady simulations are performed for a modern low-speed fan rig for which extensive measured data are available. The computational domain contains a complete fan assembly with an intake duct and the downstream outlet guide vanes (OGVs), which is a whole low-pressure (LP) domain. Flutter simulations are conducted over a range of speeds to understand flutter characteristics of this blade. Only the first flap (1F) mode is considered in this work. Measured rig data obtained by using the same fan set but with two different lengths of the intake showed a significant difference in the flutter boundary for the two intakes. AU3D computations were performed for both intakes and were used to explain this difference between the two intakes, and showed that intake reflections play an important role in flutter of this blade. This observation indicates that the experiment with the long intake used for the performance test may be misleading for flutter. In the next phase of this work, two possible modifications for increasing the flutter margin of the fan blade were explored: changing the mode shape of the blade and using acoustic liners in the casing. The results show that it is possible to increase the flutter margin of the blade by either decreasing the ratio of the twisting to plunging motion in 1F mode or by introducing deep acoustic liners in the intake. The liners have to be deep enough to attenuate the flutter pressure waves and hence influence the stability. The results indicate the importance of reflection in flutter stability of the fan blade and clearly show that intake duct needs to be included in flutter study of any fan blade.

Copyright © 2017 by ASME
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Fig. 8

1F/2ND aero-damping at HWK line

Grahic Jump Location
Fig. 7

Characteristic map with stability boundaries for the model fan used in this study

Grahic Jump Location
Fig. 6

Configuration of two intakes: (a) short intake with a lined wall and (b) long intake with a hard wall

Grahic Jump Location
Fig. 3

Instantaneous static pressure (ΔP) contour at mid chord, mref  = 0.92

Grahic Jump Location
Fig. 2

Pressure ratio versus nondimensional mass flow

Grahic Jump Location
Fig. 5

Steady downstream entropy in wake: (a) mref  = 0.956 and (b) mref  = 1.053

Grahic Jump Location
Fig. 4

Measured and computed distribution of steady stagnation pressure downstream of rotor: (a) mref  = 0.956 and (b) mref  = 1.053

Grahic Jump Location
Fig. 1

Domain used for flutter computations

Grahic Jump Location
Fig. 18

Insertion loss against liner depth/wavelength

Grahic Jump Location
Fig. 9

Cut-on frequencies upstream and downstream of the blade

Grahic Jump Location
Fig. 10

Time histories of the blade displacement

Grahic Jump Location
Fig. 11

Aerodamping for each component

Grahic Jump Location
Fig. 15

Geometry of the validation case

Grahic Jump Location
Fig. 16

Unsteady pressure profiles

Grahic Jump Location
Fig. 17

Comparison of CFD results against measured data

Grahic Jump Location
Fig. 12

Contours of blade vibration, 1F mode: (a) α = 0.2, (b) α = 0.3, and (c) α = 0.4

Grahic Jump Location
Fig. 13

Time histories of displacement (a) and aerodamping (b) for three mode shapes

Grahic Jump Location
Fig. 19

1F/2ND aero-damping for hard wall and lined wall

Grahic Jump Location
Fig. 20

1F/3ND aero-damping for a high speed fan

Grahic Jump Location
Fig. 21

Aero-damping for three lined walls

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In