Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
2000-03-07
2001-09-04
Ryznic, John E. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With heating, cooling or thermal insulation means
Changing state mass within or fluid flow through working...
C416S248000, C416S500000
Reexamination Certificate
active
06283707
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a damper for aerofoil blades and in particular a damper for aerofoil blades mounted on a rotatable disc.
BACKGROUND OF THE INVENTION
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. 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. Such vibration, if unchecked, leads to reduction in blade life and in some cases rapid damage to the blades, possibly resulting in blade failure.
Aerofoil blades commonly vibrate in a number of different modes including flap, torsional and edgewise modes. In the torsional mode of vibration, each aerofoil blade tends to twist about its longitudinal axis. In the flap mode, each aerofoil blade flaps in a generally circumferential direction. In edgewise mode each aerofoil blade tends to rock axially forward and rearward (with respect to the axis of rotation of the disc on which the aerofoil blades are mounted).
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. Such a damper is described in EP 0,509,838, and U.S. Pat. No. 5,478,207 among many others.
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.
Another proposed damping arrangement is described in GB 2078,310. In this proposal a pin is introduced within a slightly off radial extending passage provided in the aerofoil blade. This pin is retained at the blade root end whilst being free to slide within the passage. Vibration of the blade causes relative sliding movement of the pin within the passage. The friction generated will absorb energy and will then tend to damp out the vibration of the blade.
The damping provided by this arrangement is not particularly effective and the arrangement proposed requires separate passages to be provided within the blade. Furthermore, to provide adequate damping the pin has an interference fit within the passage over a substantial length and surface of the pin. This interference fit provides a loading against the sides of the passage to produce the required friction to damp the vibration. This arrangement, however, makes it difficult to fit the pin within the aerofoil blade.
It is therefore desirable to provide an aerofoil blade damper which is so configured as to provide improved effective damping of aerofoil blade vibration.
SUMMARY OF THE INVENTION
According to the present invention there is provided an aerofoil blade damper for use with an aerofoil blade which has blade root and a core passage defined in the blade root and blade which extends within the blade root and blade, the damper comprising an elongate member which in use is arranged to be inserted within a core passage, the damper being arranged to be retained in the blade at one end which is closest to the blade root with the remainder of the damper free to move relative to and within the passage; wherein the damper comprises a resilient plate insert upon which there are provided at least two discrete substantially oppositely directed contact regions which are arranged, in use, to frictionally engage the passage.
A damper which is inserted within a blade core passage incorporates discrete contact regions which provide improved damping. The discrete contact regions allow increased contact loads to be used whilst still allowing the required relative vibration induced sliding of the damper within the passage and allowing the damper to be relatively easily inserted within the passage. The increased contact loads generate increased friction which dissipates more vibrational energy so providing improved vibration damping.
Preferably the resilience of the damper is arranged to permit the damper to bend to conform to the shape of the blade passage within which the damper is arranged to be inserted. The resilience of the damper may be arranged such that the contact regions of the damper are urged against the sides of the passages and provides a contact load between the contact regions and the blade passage, when the damper is inserted within the blade passage.
Preferably in use the blade and damper are arranged to rotate about a rotational axis and the damper is arranged in use and is sufficiently resilient that centrifugal forces caused by the rotation bend and deflect at least a part of the damper to urge the contact regions against the sides of the passages.
The plate insert may be corrugated with the corrugations disposed transversely across the plate. Alternatively the corrugations may be disposed at an angle relative to an axis of the plate. The corrugations may also alternatively be disposed longitudinally. The contact regions may preferably comprise the maximum and minimum extents of the corrugations which are arranged in use to frictionally engage the passage.
A corrugated plate damper provides multiple contact regions and is simple to fabricate.
The contact regions may comprise protrusions from the plate insert. The protrusions may comprise arcuate profiled pads where the thickness of the plate insert is increased.
Preferably the protrusions comprise flexible arms extending from the plate insert, with the distil ends of the arms arranged in use to frictionally engage the passage. The arms may be angled in the direction of the end of the damper arranged to be closest to the blade root.
In operation centrifugal loading of the arms angled in the direction of the root end of the damper will, in use, urge the arms and contact regions on the ends of the arms into further engagement with the passage. This provides or increases the contact load on the contact regions, providing or increasing the friction generated under vibration induced sliding of the contact regions. This improves the dissipation of the vibrational energy and damping provided by such a damper.
An additional mass may be provided at each of the distil ends of the arms.
The additional mass on each of the ends of the arms increases the centrifugal loading produced on the contact regions under operation.
The protrusions may extend from only one side of the plate, the protrusions and the opposite side of the plate arranged to provide the contact regions which, in use, frictionally engage the passage.
Preferably the successive contact regions are arranged alternately along the length of the damper.
Preferably the damper is arranged to be used with a turbine blade. Furthermore the core passage within which the damper is arranged to be inserted may comprise a cooling passage within an aerofoil blade.
By arranging the damper so that it can be inserted within the cooling passages of a turbine blade separate passages for the damper do not need to be provided within the blade. This simplifies the overall design and improves the integrity of the blade within which the damper is arranged to fit.
Alternatively the core passage within which the damper is arranged to be inserted may comprise a dedicated passage within an aerofoil blade for the damper.
Preferably at the end of the damper arranged to be closest to the blade root a head portion extends from the plate insert and is arranged to span the width of the passage to thereby provide retention of the damper when inserted into a blade.
The head portion provides a simple and secure means for locating the root end of the damper.
Preferably the head portion
Manelli Denison & Selter PLLC
Rolls-Royce plc
Ryznic John E.
Taltavull W. Warren
LandOfFree
Aerofoil blade damper does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aerofoil blade damper, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aerofoil blade damper will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2472697