GB2112466A

GB2112466A - Rotor blade vibration damping

Info

Publication number: GB2112466A
Application number: GB08139037A
Authority: GB
Inventors: Phillip Ivor Christie
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1981-12-30
Filing date: 1981-12-30
Publication date: 1983-07-20

Abstract

Each damper comprises a generally "V" shaped member 20, the extremities 22 of the limbs 21 of which engage the shanks of the blades 14 and are urged against the platforms and the shanks by centrifugal forces. Located in the tapering void between each shank and the limbs 21 of the member 20 is a resilient body 30 such as an elastomeric material. Centrifugal forces on the bodies 30 urge the bodies 30 into contact with the shanks 14 of the blades 12 and the limbs 21 and thereby exerts circumferential forces on the blades 12 to damp vibrations. <IMAGE>

Description

SPECIFICATION Rotor for fluid flow machines This invention relates to a rotorforfluid flow machines.

It is known for such a rotor to comprise a rotor body, an annular array of blades connected to the body at the periphery thereof, each blade having a radial part projecting radially from the body and a circumferential part projecting circumferentially from the radial part at the radially outer end thereof.

It is an object of the invention to provide an improved means for opposing excitation of the blades into circumferential modes of vibration. It is known to do that by a device acting primarily at radially inwardly facing surfaces of the circumferential parts of adjacent blades or acting at confronting edge regions of said circumferential parts. However, the efficiency of the known device is adversely affected by the fact that the adjacent circumferential parts are not always accurately aligned, e.g. in the sense that a step may occur at their adjacent edges, so that it is difficult to maintain satisfactory cooperation between the device and said circumferential parts.

The difficulty is overcome or reduced by the rotor claimed in Claim 1 hereto. By being urged circumferentially into engagement with the radial parts of the blade in response to centrifugal force, and having regard to the fact that the centrifugal force can be of high magnitude, the elements can be highly effective in opposing circumferential excitation.

An example of a rotor according to this invention will now be described with reference to the accompanying drawing wherein: Figure 1 is part of the rotor seen in axial elevation, and, Figure2 is a section on the line ll-ll in Figure 1.

The rotor comprises a rotor body 10 and an annular array of blades 12. Each blade 12 comprises a root part 13 whereby the blade is connected to the rotor, an inner radial part 14 projecting radially from the periphery, 11, of the body 10, circumferential parts 15 projecting circumferentially from the inner radial part at the radially outer end thereof, and an outer radial part or aerofoil 16, being an extension of the inner radial part. The circumferential parts 15 define the radially inner border of a fluid flow passage 16 between the parts 15 as is wellunderstood per se.

Each two adjacent blades 12 have arranged therebetween a damping member 20 being a V-shaped metal part positioned for the limbs 21 of the member defining the "V" to be divergent in the radially outward sense. The free extremities, 22, of the limbs 21 lie in the corners, 23, defined by the junction of the adjacent radial and circumferential parts 14,15.

The medial portion, 24, of the member 20 lies radially inwards of the extremities 22, and the member 20 is pliant to the degree that centrifugal force acting on the member 20 during rotation of the rotor causes the extremities 22 to be urged into the corners 23 and apply to the adjacent blades at least component forces F which act circumferentially on the radial parts 14. In other words, the limbs 21 define elements urged circumferentially into en gagementwith the radial parts 14 by the medial portion 24 responsive to centrifugal force acting thereon. The forces F damp vibration of the blades in the circumferential sense or oppose the excitation of such vibration.

The medial portion 24 of the member 20 may be shaped to engage a recess 25 in the periphery of the disc whereby the member 20 is adequately located in position in the space between the radial parts 14.

In addition to the member 20 there may be provided elements 30 arranged between the pair of convergent surfaces 31,32 defined by each limb 21 and the adjacent radial part 14. The elements 30 are made of a material capable of flowing under centrifugal force, e.g. an elastomeric material, so as to co-operate with the surfaces 31,32 to exert circumferential forces on the respective radial parts 14. The material of the elements 30 may be rubber and the latter may contain metallic inserts. The member 20 may be constructed, by virtue of its pliancy, to contribute to the circumferential forces. Alternatively these forces are provided substantially wholly by the elements 30.

1. Rotorforfluid flow machine comprising a rotor body; an annular array of blades connected to the body at the periphery thereof; each blade having a radial part projecting radially from the periphery of the body and a circumferential part projecting circumferentially from the radial part at the radially outer end thereof; two elements arranged between the radial parts of each two adjacent blades; and urging means, responsive to centrifugal force due to rotation of the rotor, for urging the elements circumferentially into engagement with the respective radial parts to exert a circumferential force thereon.

2. Rotor according to Claim 1 comprising a member extending between said radial parts, the member having end portions situated adjacent the respective parts and defining said elements, the member having a medial portion situated radially inwardly of the end portions, and the member being sufficiently pliant for a said centrifugal force acting on the medial portion to urge the end portions into engagement with the respective radial parts to exert said circumferential force thereon.

3. Rotor according to Claim 2 wherein said end portions are arranged for free extremities thereof to be situated at the junctions of the radial parts and the respective said circumferential parts.

4. Rotor according to Claim 2 or Claim 3 wherein said member is generally V-shaped and positioned for the limbs of the "V" to be divergent in the radially outward sense.

5. Rotor according to Claim 1 comprising a member extending between said radial parts, substantially clear of said circumferential parts, the member being shaped so that a pair or radially outwardly convergent surfaces is defined by the member and each of the radial parts, and wherein a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Rotor for fluid flow machines This invention relates to a rotorforfluid flow machines. It is known for such a rotor to comprise a rotor body, an annular array of blades connected to the body at the periphery thereof, each blade having a radial part projecting radially from the body and a circumferential part projecting circumferentially from the radial part at the radially outer end thereof. It is an object of the invention to provide an improved means for opposing excitation of the blades into circumferential modes of vibration. It is known to do that by a device acting primarily at radially inwardly facing surfaces of the circumferential parts of adjacent blades or acting at confronting edge regions of said circumferential parts. However, the efficiency of the known device is adversely affected by the fact that the adjacent circumferential parts are not always accurately aligned, e.g. in the sense that a step may occur at their adjacent edges, so that it is difficult to maintain satisfactory cooperation between the device and said circumferential parts. The difficulty is overcome or reduced by the rotor claimed in Claim 1 hereto. By being urged circumferentially into engagement with the radial parts of the blade in response to centrifugal force, and having regard to the fact that the centrifugal force can be of high magnitude, the elements can be highly effective in opposing circumferential excitation. An example of a rotor according to this invention will now be described with reference to the accompanying drawing wherein: Figure 1 is part of the rotor seen in axial elevation, and, Figure2 is a section on the line ll-ll in Figure 1. The rotor comprises a rotor body 10 and an annular array of blades 12. Each blade 12 comprises a root part 13 whereby the blade is connected to the rotor, an inner radial part 14 projecting radially from the periphery, 11, of the body 10, circumferential parts 15 projecting circumferentially from the inner radial part at the radially outer end thereof, and an outer radial part or aerofoil 16, being an extension of the inner radial part. The circumferential parts 15 define the radially inner border of a fluid flow passage 16 between the parts 15 as is wellunderstood per se. Each two adjacent blades 12 have arranged therebetween a damping member 20 being a V-shaped metal part positioned for the limbs 21 of the member defining the "V" to be divergent in the radially outward sense. The free extremities, 22, of the limbs 21 lie in the corners, 23, defined by the junction of the adjacent radial and circumferential parts 14,15. The medial portion, 24, of the member 20 lies radially inwards of the extremities 22, and the member 20 is pliant to the degree that centrifugal force acting on the member 20 during rotation of the rotor causes the extremities 22 to be urged into the corners 23 and apply to the adjacent blades at least component forces F which act circumferentially on the radial parts 14. In other words, the limbs 21 define elements urged circumferentially into en gagementwith the radial parts 14 by the medial portion 24 responsive to centrifugal force acting thereon. The forces F damp vibration of the blades in the circumferential sense or oppose the excitation of such vibration. The medial portion 24 of the member 20 may be shaped to engage a recess 25 in the periphery of the disc whereby the member 20 is adequately located in position in the space between the radial parts 14. In addition to the member 20 there may be provided elements 30 arranged between the pair of convergent surfaces 31,32 defined by each limb 21 and the adjacent radial part 14. The elements 30 are made of a material capable of flowing under centrifugal force, e.g. an elastomeric material, so as to co-operate with the surfaces 31,32 to exert circumferential forces on the respective radial parts 14. The material of the elements 30 may be rubber and the latter may contain metallic inserts. The member 20 may be constructed, by virtue of its pliancy, to contribute to the circumferential forces. Alternatively these forces are provided substantially wholly by the elements 30. CLAIMS

5. Rotor according to Claim 1 comprising a member extending between said radial parts, substantially clear of said circumferential parts, the member being shaped so that a pair or radially outwardly convergent surfaces is defined by the member and each of the radial parts, and wherein a said element is provided between the surfaces of each said pair, and each said element is adapted to cooperate with the surfaces of the pair to exert a said circumferential force on the adjacent radial member when the further member is subject to a said centrifugal force.

6. Rotor according to Claim 5 wherein said elements are made of a material capable of flowing in response to said centrifugal force.

7. Rotor for fluid flow machine substantially as described herein with reference to the accompanying drawing.