Fluid reaction surfaces (i.e. – impellers) – Rotor having flow confining or deflecting web – shroud or... – Axially extending shroud ring or casing
Reexamination Certificate
1999-11-12
2001-07-31
Lopez, F. Daniel (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Rotor having flow confining or deflecting web, shroud or...
Axially extending shroud ring or casing
C416S22300B
Reexamination Certificate
active
06267557
ABSTRACT:
This invention relates to a damper for aerofoil blades and in particular a damper for aerofoil blades mounted on a rotatable disc.
Gas turbine engines for aircraft, marine and land use typically have axial flow turbines that comprise a number rotatable discs, each of which carries an annular array of radially extending aerofoil blades on its periphery. Each aerofoil blade is provided with a root portion by means of which it is attached to its associated disc, and a platform positioned between its aerofoil portion and root portion. While such a method of attachment is effective in ensuring the integrity of each blade/disc assembly, problems can still arise as a result of aerofoil blade vibration. Aerofoil blades commonly vibrate in both flap and torsional modes. In the torsional mode of vibration, each aerofoil blade tends to twist about its longitudinal axis whereas in the flap mode, each aerofoil blade flaps in a generally circumferential direction.
It is well known to combat flap and torsional modes of aerofoil blade vibration by the provision of damping members that are configured and positioned so that one damping member spans the undersides of the platforms of circumferentially adjacent aerofoil blades. Centrifugal loading due to disc rotation urges the damping members into engagement with the platform undersides. Damping is provided by frictional interaction between the dampers and blade platforms.
While such damper members are effective in damping torsional and flap modes of vibration, they are less effective in dealing with edgewise modes of vibration. Edgewise modes of vibration are characterised by bending of each aerofoil blade in forward and rearward directions (with respect to the axis of rotation of the disc on which the aerofoil blades are mounted).
It is an object of the present invention to provide an aerofoil blade damper which is so configured as to provide effective damping of edgewise modes of aerofoil blade vibration.
According to the present invention, a damping member for damping vibration of aerofoil blades mounted on a rotary disc, which aerofoil blades are provided with platforms in radially spaced apart relationship with said disc, comprises a first portion for operationally and simultaneously engaging the platforms of a pair of circumferentially adjacent aerofoil blades, and second and third portions extending from said first portion for operationally engaging a peripheral surface on said disc, said second and third portions converging from a spaced apart relationship with each other at said first portion into operational engagement with each other adjacent said disc peripheral surface.
Frictional interaction between the second and third portions, and between the disc peripheral surface and the second and third portions give rise to the damping of edgewise modes of aerofoil blade vibration.
Said second and third portions are preferably formed from sheet material.
Said sheet material may be metallic.
Said first, second and third portions may be integral.
Said second and third portions may be of curved cross-section configuration at their region of contact with each other and with disc peripheral surface.
A fourth portion may be provided to interconnect said second and third portions intermediate the extents of said second and third portions.
Said fourth portion may be formed from sheet material and be of curved cross-sectional configuration.
Said first position is preferably of generally cylindrical configuration.
REFERENCES:
patent: 4101245 (1978-07-01), Hess et al.
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patent: 4655687 (1987-04-01), Atkinson
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patent: 2112466 (1983-07-01), None
Lopez F. Daniel
Manelli Denison & Selter PLLC
McAleenan James M.
Rolls-Royce plc
Taltavull W. Warren
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