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ON THE IMPORTANCE OF ENGINE-REPRESENTATIVE MODELS FOR FAN FLUTTER PREDICTIONS

[+] Author and Article Information
Sina C. Stapelfeldt

Vibration University Technology Centre, Mechanical Engineering Department, Imperial College London, London SW7 2AZ, United Kingdom
sina.stapelfeldt@ic.ac.uk

Mehdi Vahdati

Vibration University Technology Centre, Mechanical Engineering Department, Imperial College London, London SW7 2AZ, United Kingdom
m.vahdati@ic.ac.uk

1Corresponding author.

ASME doi:10.1115/1.4040110 History: Received November 07, 2017; Revised November 17, 2017

Abstract

This paper examines the factors which can result in discrepancies between rig tests and numerical predictions of the flutter boundary for fan blades. Differences are usually attributed to the deficiency of CFD models for resolving the flow at off-design conditions. This work was initiated as a result of inconsistencies between the flutter prediction of two rig fan blades. A new set of flutter computations for both blades with varying detail in the computational models were performed to investigate these inconsistencies. The results of this work indicate that the previous discrepancies between CFD and tests were due to: 1. Differences in the effectiveness of the acoustic liner in attenuating the pressure wave created by the blade vibration as a result of differences in flutter frequencies between the two fan blades. 2. Differences in the level of unintentional mistuning of the two fan blades due to manufacturing tolerances. In the second part of this research, the effects of blade misstaggering and inlet temperature on aerodynamic damping were investigated. The data presented in this paper clearly show that manufacturing and environmental uncertainties can play an important role in the flutter stability of a fan blade. They demonstrate that aeroelastic similarity is not necessarily achieved if only aerodynamic properties and the traditional aeroelastic parameters, reduced frequency and mass ratio, are maintained. This emphasises the importance of engine-representative models, in addition to an accurate and validated CFD code, for the reliable prediction of the flutter boundary.

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