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METHOD FOR PREDICTING ICE-INDUCED UNSTABLE FAN WHIRL

IP.com Disclosure Number: IPCOM000247694D
Publication Date: 2016-Sep-27
Document File: 8 page(s) / 221K

Publishing Venue

The IP.com Prior Art Database

Abstract

A method is provided for predicting unstable fan whirl in a gas turbine engine turbofan caused by ice shedding.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 33% of the total text.

Page 01 of 8

METHOD FOR PREDICTING ICE-INDUCED UNSTABLE FAN WHIRL

ABSTRACT


[0001] A method is provided for predicting unstable fan whirl in a gas turbine engine turbofan caused by ice shedding.

BACKGROUND


[0002] Turbofan engines are commonly used for aircraft propulsion. A turbofan engine includes a fan rotor having a disk mounted for rotation in one or more bearings and carrying an array of large-diameter fan blades. The blades are closely surrounded by a casing, leaving a small predetermined radial clearance between the blade tips and the casing. The casing may incorporate an abradable material which serves as a sacrificial element in the event of contact between the tips of the blades and the casing.


[0003] In operation, the fan rotor may experience "whirl" which may be described as combined rotation and radial deflection. Whirl may be caused, for example, by the rotor being unbalanced relative to its central axis (i.e. the rotor's center of mass is not coaxial with its central axis).


[0004] Ordinarily, some whirl is expected and is accommodated by the bearing system, the provided clearances, and the properties of the abradable material. This is referred to as stable whirl.


[0005] In some circumstances, when the blade tips contact the casing, tangential forces generated by the interaction of the blade tips and the casing can cause a positive feedback loop called unstable whirl (whirl instability). This can lead to an uncontrolled increase in radial deflection of the blades and can result in damage to or failure of components such as the bearings, blades, and/or the casing.


[0006] Described herein is a method for predicting the occurrence of fan whirl instability.

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Page 02 of 8

BRIEF DESCRIPTION OF THE DRAWINGS


[0007] The concept may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures, in which:


[0008] FIG. 1 is a schematic, partially-sectioned perspective view of a fan section of a gas turbine engine;


[0009] FIG. 2 is a schematic cross-sectional view of a fan section of a gas turbine engine; and


[0010] FIG. 3 is a block diagram of a fan whirl stability projection method.

DETAILED DESCRIPTION OF THE CONCEPT


[0011] Illustrated in FIGS. 1 and 2 is a turbofan engine 10. The engine 10 is axisymmetrical about a centerline axis "A" and includes a fan 12 suitably mounted coaxially inside a surrounding annular fan casing 14. The fan 12 includes a row of fan blades 16 extending radially outwardly in span from a rotor disk 18. As shown in FIG. 2, the rotor disk 18 is mounted for rotation in one or more bearings 20.


[0012] The tips 22 of the fan blades 16 have a predetermined radial clearance "C" from the fan casing 14. The casing 14 may incorporate a ring of an abradable material 24 such as phenolic resin, metallic honeycomb, or the like. The purpose of the abradable material 24 is to serve as a sacrificial element should the tips 22 exceeded the provided clearance C.


[0013] Dur...