GB2043797A

GB2043797A - Bladed Rotor for Gas Turbine Engine

Info

Publication number: GB2043797A
Application number: GB7908522A
Authority: GB
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1979-03-10
Filing date: 1979-03-10
Publication date: 1980-10-08
Also published as: IT1130017B; IT8020480A0; JPS55123303A; FR2451452A1; DE3008890A1

Abstract

The rotor (15) has fir-tree root fixings at its periphery supporting blades (16). In order to damp blade vibration, the under sides of platforms (20) are engaged by damping weights (36) freely carried on segmental plates (23, 31) secured to the rotor (15) by hollow rivets 28. <IMAGE>

Description

SPECIFICATION Bladed Rotor for a Gas Turbine Engine This invention relates to a bladed rotor for a gas turbine engine.

Bladed rotors for gas turbine engines normaily comprise blade carrying discs each of which has a plurality of retaining slots in its periphery with which engage the roots of the blades themselves.

One problem which arises with these constructions lies in the vibration of the blades, which is unrestrained may lead to the blades breaking up or other deleterious effects. This problem is common to most types of rotor blades although it is most serious in the case of unshrouded blades, that is blades whose tips are not connected or integral with a circumferentially extending shroud.

In order to solve this problem it has been suggested in the past that dampers should be used. One popular form of damper comprises a weight or weights having a degree of radial freedom such as to allow it to bear on the under surface of the blade platform. However, the constructions proposed in the past have necessitated either having the weights complete free and therefore liable to produce unexpected results or retained to part of the blade which then affects the vibration of the blade in such a way as to make the effect of the weights themselves less powerful.

The present invention provides a way of damping the blade vibration which avoids these problems.

According to the present invention a bladed rotor for a gas turbine engine comprises a rotor disc having root fixings at its periphery which support a row of rotor blades, each blade comprising a platform which adjoins the similar platforms of adjacent blades to define an annular wall, front and rear annular arrays of segmental plate members attached to the disc so that they lie against the front and rear faces of the disc periphery and separate front and rear damping weights retained to the front and rear plates respectively so that they are free to move radially outwards sufficiently to frictionally engage the inner surfaces of the platforms.

Preferably the damping weights engage the platforms adjacent to where they adjoin with the platforms of the neighbouring blades. Thus each weight may engage two said platforms.

In a preferred embodiment the weights have angled outer faces in the form of a shallow wedge which engage with correspondingly angled faces on the inner surface of the platform.

The plates which support the weights may be sealing plates and they may be attached to the disc by a rivet, pin or similar fastening.

The invention will now be particularly described merely by way of example and with reference to the accompanying drawings in which; Figure 1 is a partly broken away view of a gas turbine engine have a bladed rotor in accordance with the present invention, Figure 2 is a radial section through the rotor disc of Figure 1, Figure 3 is a section on the line 3-3 of Figure 2 and, Figure 4 is a view on the arrow 4 of Figure 2.

In Figure 1 there is shown a gas turbine engine comprising a casing 10 within which there are mounted in flow series a compressor 11, a combustuion chamber 12 and a turbine 13. The casing 10 forms a final nozzle 14. Operation of the engine overall is conventional and is not elaborated in the specification.

The casing is broken away in the region of the turbine 1 3 to expose to view the bladed rotor which forms the turbine rotor of the engine. This rotor comprises a disc 1 5 from which are supported a row of turbine blades 1 6. The details of the disc 1 5 and blades 1 6 may be seen in Figures 2 and 3.

The disc 1 5 is provided at its periphery with a plurality of axially extending retaining slots 1 7. In the present embodiment the slots 1 7 are of the well known fir tree section. In each of the slots 1 7 there engages one of the correspondingly shaped roots 18 of the blade 1 6. The root 1 8 carries a shank portion 19 which in turn carries a platform 20 an and aerofoil 22. The platform 20 and aerofoil 22 perform the aerodynamic function of the blade, the platform 20 defining the inner boundary of the hot gas flow through the stage while the aerofoils 22 extract work from the hot gas.

Clearly there are some additional considerations to be taken into account in the design of the rotor. Thus it is necessary to prevent hot gases escaping underneath the platform 20 and thus bypassing the aerofoil 22 and because the aerofoil 22 is unrestrained at its tip it is necessary to provide some kind of damping for the blade as a whole.

In order to prevent leakage of the hot gas sealing plates 23 are provided. In the present instance these plates are retained to the rear face of the disc 1 5 and they extend between a groove 24 formed in the rear face of the disc and the end faces 25 of the platforms 20. It will be seen from Figure 4 that the plates 23 are segmental and that together they form a complete annulus.

In order to retain the plates 23 in position each plate is provided with a pair of circular bosses 26 with which engage heads 27 of two hollow rivets 28. The rivets 28 each pass through one of the apertures 29 drilled through the peripheral portion of the disc which lies between two of the fir tree slots 1 7. In the present case each of the rivets 28 is peened over at its other end to engage with cylindrical bosses 30 formed in a front assembly of plates 31. It will be seen from Figure 3 that the plates 31 do not act as sealing plates since they have a cut-away form but they are in fact used to support damping means which are described below.

It will be seen that as so far described the plates 23 and 31 are solely supported by the engagement of the rivets 28 with the peripheral portions of the disc 1 5. We have found that in spite of the general rule that the rim area of a rotor disc is heavily loaded and should not therefore be provided with apertures or other stress raising features, this area between the slots 1 7 is relatively lightly loaded, and far from increasing the stresses carried by the disc the provision of these holes 29 may in fact improve the position.

As mentioned above it is also necessary that some form of damping should be provided for the blades. To this end each of the plates 23 and 31 is provided with a pair of retaining studs 32 and 33. The studs 32 and 33 are identical and comprise a head portion 34 which engages with the respective plate and a squared-off portion 35 which extends inwardly of the plate into the space between the shanks 1 9. On each of the squaredoff portions 35 there is engaged a corresponding damper weight. Each of the weights 36 comprises a supporting portion 37 relatively thin in section and having a central radially extending groove which engages the squared-off portion 35 so as to allow the weight substantial radial freedom and a smail degree of circumferential freedom and freedom to twist.The outer portion of each weight 36 comprises a heavier section at 38 formed at its outermost extremity with a pair of angled faces 39 forming a shallow wedge.

Each of the weights 36 is arranged to be circumferentially aligned with the junction between two of the platforms 20. Each of the platforms 20 has adjacent to its edge which adjoins the neighbouring platform an angled face 40 whose angle is arranged to match that of the corresponding face 39 of the damper 36.

It will be seen that when the rotor rotates the weights 36 will be forced outwards and will therefore engage with the two faces 40 of the respective adjoining platforms 20. Each platform 20 will be subject to the effect of four of the weights one at each corner. Vibrational movement of the blade which will reflect in movement of the platforms 20 will therefore be damped by the energy involved being converted to heat when the platform moves relative to the damper weight 36.

It will be seen therefore that the present construction provides a way in which the plates 23 and 31 may be supported directly from the disc 1 5. These plates do not therefore have any effect on the vibration characteristics of the blade, and the full effect of the length of the shank 1 9 is operational to maximise the effect of dampers 36.

The plates 23 are supported by the rivets 28 approximately at their mid-radius. This is clearly the best position to support them to allow them to bear gas loads caused by hot gases attempting to flow underneath the platform 20.

It will be appreciated that there are a number of modifications which could be made to the embodiment described. In particular the hollow rivets 28 could be replaced by other forms of fixing pins or even threaded bolts which would then be reuseable. The plates 23 and 31 could be interchanged or they could both be made as complete sealing plates. The damper weights 36 could be supported from the plates 23 and 31 by other means than the studs 32 described.

Claims

1. A bladed rotor for a gas turbine engine comprising a rotor disc having root fixings at its periphery which supports a row of rotor blades, each blade comprising a platform which adjoins the platforms of the adjacent blades to define an annular wall, front and rear annular areas of segmental plate members attached to the disc so that they lie against the front and rear faces of the disc periphery and separate front and rear damping weights retained to the front and rear plates respectively so that they are free to move radially outward sufficient to frictionally engage the inner surfaces of the platforms.

2. A bladed rotor as claimed in Claim 1 and in which said damping weights engage said platforms adjacent to where they adjoin with the platforms of adjacent blades.

3. A bladed rotor as claimed in Claim 2 and in which each said weight engages with the platforms of two said adjacent blades.

4. A bladed rotor as claimed in Claim 3 and in which said platforms comprise angled inner surfaces and the weights comprise correspondingly angled outer surfaces which form a shallow wedge and engage with the angled surfaces of the platforms.

5. A bladed rotor as claimed in any preceding claim and in which each said damping weight comprises a longitudinally extending slot which engages with a projection from one of said plates to retain the weight to the plate.

6. A bladed rotor as claimed in any preceding claim and in which one said annular area of plate members forms a seal between said platform members and said disc.

7. A bladed rotor as claimed in any preceding claim and in which said plates are retained to said disc by a rivet pin or the like.

8. A bladed rotor substantially as hereinbefore particularly described with reference to the accompanying drawings.

9. A gas turbine engine having a bladed rotor as claimed in any preceding claim.