GB2255138A

GB2255138A - Bladed disc having a damping element

Info

Publication number: GB2255138A
Application number: GB9203017A
Authority: GB
Inventors: Gerard Gabriel Miraucourt; Jacky Naudet
Original assignee: Societe Nationale dEtude et de Construction de Moteurs dAviation SNECMA; SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1991-03-27
Filing date: 1992-02-13
Publication date: 1992-10-28
Anticipated expiration: 2012-02-13
Also published as: GB2255138B; FR2674569A1; GB9203017D0; FR2674569B1

Abstract

A unitary bladed disc 1 for a turboshaft engine is provided with at least one annular damper element 7 located in a respective circumferentially extending groove 5 in the underside of the blade platforms 4, the damper element having at least one scalloped portion (8 fig. 3) defining a plurality of radially inwardly directed projections (9) and recesses (10) arranged alternately in succession around the element 50 that, in operation, dynamic imbalances generating frictions which have a damping effect on vibrations of the blades 2 are created under centrifugal action. in an alternative arrangement (figure 4) the damper is located in a groove (105) on the undersides of the platforms and in a groove (105a) in a radially outwardly facing surface of the disc and may be provided with axially directed projections (108) and recesses (110) (fig 5). <IMAGE>

Description

UNITARY BLADED DISC WITH VIBRATION DAMPING MEANS The present invention relates to a bladed disc of the unitary type for a turboshaft engine, the disc comprising means for damping vibrations during operation.

Various solutions have already been proposed and used to damp vibrations which occur in rotating bodies during operation of a turboshaft engine, particularly when passing through certain critical thresholds at high rotational speeds and under the influence of load variations.

US Patent No. 4 347 040 discloses one example of the techniques used and shows a turboshaft engine rotor composed of a disc and a plurality of blades, and having T-section elements forming dampers, each being arranged under two consecutive blade platforms.

Published French Application No. 2 413 542 shows another example of a blade damper which exerts an axial force on the blade root as a result of the effect of centrifugal force.

However, no fully satisfactory solution has been proposed for applications where the blades of a turboshaft engine rotor form a single unitary assembly with a disc or ring forming the support for the blades.

To this end, according to the invention, a unitary bladed disc for a turboshaft engine comprises a body in the form of a disc or ring, a plurality of blades integral with the body, and platforms carried by the body in the region of the junction between the blades and the body for defining part of the main fluid flow path of the engine, the platforms having a circumferentially extending groove in the undersurface thereof, and the unitary bladed disc being provided with a damper element of generally annular shape placed in the groove, the damper element having at least one scalloped portion defining a plurality of projections and recesses arranged alternately in succession around the damper element whereby, in operation, dynamic imbalances generating frictions which have a damping effect on vibrations of the blades are created under centrifugal action.

Preferred features of the invention will become apparent from the following description of two preferred embodiments of the invention, given by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic axial section through part of a first embodiment of a unitary bladed disc provided with a damper in accordance with the invention; Figure 2 is a half-axial sectional view, to a larger scale, of the damper incorporated in the embodiment shown in Figure 1; Figure 3 is a perspective view of the damper illustrated in Figures 1 and 2; Figure 4 is a diagrammatic view similar to that of Figure 1, but showing a second embodiment of a unitary bladed disc having a damper in accordance with the invention; and, Figure 5 is a view of part of the damper incorporated in the embodiment shown in Figure 4, looking in the direction indicated by the arrow F1.

A unitary bladed disc 1 for a turboshaft engine comprises, as shown by way of example in Figure 1, a plurality of blades 2 integral with a disc 3. In addition, the disc 3 carries platforms 4 in the region of the junction with the aerodynamic portions of the blades 2, the radially outer surfaces of the platforms 4 defining part of the main fluid flow path of the turboshaft engine. This general construction is well known.

In the first embodiment of the invention shown in Figure 1, on each side of the disc 3, i.e. upstream and downstream with respect to the normal direction of flow of gases in the turboshaft engine, a circumferentially extending annular groove 5,6 respectively is provided in the radially inner surface of the platforms 4, and a damper 7 is disposed in the upstream groove 5. The damper 7 is in the form of a transversely split annular element having a section with a U-profile. As best shown in Figures 2 and 3, the damper 7 has a scalloped and segmented portion 8 at each side and on each limb of the U, each scalloped portion 8 defining a succession of radially inwardly directed projections 9 and recesses 10 arranged alternately around the damper so as to create imbalances.In operation, under the effect of centrifugal forces, the dynamic imbalances created generate frictions under the platforms 4, thus providing the desired damping of the vibrations induced in the blades 2. The damper 7 is mounted in the groove 5 by spring action using the split 11.

Depending upon the application and the results to be obtained, the damper 7 may be placed in the upstream groove 5 as shown in Figure 1, or in the downstream groove 6, or dampers may be placed in both grooves 5 and 6 at the same time.

The section of the grooves 5 and 6 may be arranged, depending on the application, so as to have a shape evolving from the rectangular to a shape comprising radiussed angles of more or less substantial radius.

In the second embodiment shown in Figures 4 and 5, grooves 105 and 106 similar to those in the first embodiment are provided on the radially inner faces of the platforms 104 on the upstream and downstream sides of the disc 103, and an additional groove 105a is provided on an axially directed part 103a adjoining the disc 103 so that the grooves 105 and 105a lie facing each other in the same radial plane. These grooves 105 and 105a form housings for radially inner and outer edges 107a and 107b of a damper 107 which has a scalloped portion 108 offset in a generally axial direction towards the disc 103.

This scalloped portion 108 has alternating projections 109 and recesses 110 as shown diagrammatically in Figure 5, and is located under the platforms 104 so that it follows the profile of the undersurface thereof. The operation of the damper 107 is similar to that in the first embodiment, vibrations of the blades 102 being damped by the friction of the projections 109 under the platforms 104.

As in the first embodiment, depending on the application, the damper may be placed either on the upstream side or on the downstream side of the disc 103, or dampers may be provided on both sides at the same time.

Claims

1. A unitary bladed disc for a turboshaft engine, comprising a body in the form of a disc or ring, a plurality of blades integral with the body, and platforms carried by the body in the region of the junction between the blades and the body for defining part of the main fluid flow path of the engine, the platforms having a circumferentially extending groove in the undersurface thereof, and the unitary bladed disc being provided with a damper element of generally annular shape placed in the groove, the damper element having at least one scalloped portion defining a plurality of projections and recesses arranged alternately in succession around the damper element whereby, in operation, dynamic imbalances generating frictions which have a damping effect on vibrations of the blades are created under centrifugal action.

2. A unitary bladed disc according to claim 1, in which the annular damper element is transversely split to permit mounting of the damper element in the groove by spring action.

3. A unitary bladed disc according to claim 1, in which the projections of the scalloped portion are directed radially inwardly.

4. A unitary bladed disc according to claim 3, in which the annular damper element has two radially inwardly directed scalloped portions at opposite sides of the element.

5. A unitary bladed disc according to claim 1, in which the annular damper element has radially inner and outer edges, and the body has an adjoining axially directed part provided with an outwardly facing groove, the outer edge of the damper element fitting in the groove in the undersurface of the platforms, and the inner edge of the damper element fitting in the outwardly facing groove in the axially directed part, and in which the scalloped portion of the damper element is disposed so that, in operation, centrifugal action causes the projections of the scalloped portion to come into frictional engagement with the undersurface of the platforms.

6. A unitary bladed disc according to claim 1, in which the annular damper element is disposed on the upstream side of the body relative to the normal direction of gas flow in the engine.

7. A unitary bladed disc according to claim 1, in which the annular damper element is disposed on the downstream side of the body relative to the normal direction of gas flow in the engine.

8. A unitary bladed disc according to claim 1, in which the disc is provided with two annular damper elements, the damper elements being disposed one on the upstream side and the other on the downstream side of the body relative to the normal direction of gas flow in the engine.

9. A unitary bladed disc according to claim 1, substantially as described with reference to Figures 1 to 3 or Figures 4 and 5 of the accompanying drawings.