INTERMEDIATE CASING GUIDE VANE WHEEL

Abstract

An OGV wheel comprising guide vanes made of polymer matrix composite material reinforced by fibers, each having a vane root and a vane tip, the vane roots being fastened on a hub of the wheel by first connection means and the vane tip being fastened on an outer shroud of the wheel by second connection means, the first connection means including a bearing plane secured to the hub and a first backing plate for securing to the hub, the vane roots being sandwiched between the bearing plane and the first backing plate, and the second connection means including a second backing plate for securing to the shroud, the vane tip being sandwiched between the shroud and the second backing plate.

Claims

1. An OGV wheel comprising guide vanes made of polymer matrix composite material reinforced by fibers, each having an airfoil, a vane root, and a vane tip, said vane roots being fastened to a hub of said wheel by first connection means and said vane tip being fastened to an outer shroud of said wheel by second connection means, wherein said first connection means include a bearing plane secured to said hub and a first backing plate for securing to said hub, said vane roots being sandwiched between said bearing plane and said first backing plate, and said second connection means include a second backing plate for securing to said shroud, said vane tip being sandwiched between said shroud and said second backing plate.

2. The OGV wheel according to claim 1, wherein each of said vane roots and of said vane tips is formed by two half-platforms defining connection fillets over the entire width of said airfoil and connecting said airfoil with said half-platforms.

3. The OGV wheel according to claim 2, wherein said first and second backing plates include curved side edges for fitting closely against said connection fillets.

4. The OGV wheel according to claim 2, wherein each of said first and second backing plates is made up of two independent portions, each associated with respective half-platforms of two adjacent airfoils of said wheel.

5. The OGV wheel according to claim 1, wherein said first and second backing plates are common to two adjacent airfoils of said wheel.

6. The OGV wheel according to claim 1, wherein said bearing plane and said shroud for receiving respectively said vane roots and said vane tips are covered in an elastomer material.

7. The OGV wheel according to claim 1, wherein said bearing plane and said shroud for receiving respectively said vane roots and said vane tips are covered in a metal or any other analogous material that is softer than a material forming said backing plate.

8. The OGV wheel according to claim 1, wherein said first and second backing plates are fastened to said hub and said shroud respectively by bolts.

9. The OGV wheel according to claim 1, wherein said fibers are woven in two dimensions and arranged in superposed layers in order to form a three-dimensional preform.

10. The OGV wheel according to claim 1, wherein said fibers are woven in three dimensions.

11. The OGV wheel according to claim 2, wherein the two half-platforms are obtained by non-interlinking in the weaving of the fibers of said vanes so as to define over the entire width of said airfoil and on either side thereof the connection fillets connecting said airfoil with said half-platforms.

12. The OGV wheel according to claim 1, wherein said hub is an intermediate casing hub and said shroud is an intermediate casing shroud (ICS 18).

13. An aircraft engine including an OGV wheel according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings, which show an embodiment having no limiting character. In the figures:

[0023] FIG. 1 is a perspective view of a first embodiment of an OGV wheel in accordance with the invention;

[0024] FIGS. 2 and 3 show details of the OGV platform;

[0025] FIG. 4 is a view on plane IV-IV of FIG. 1 showing the support of the OGV platform in detail;

[0026] FIG. 5 is a perspective view of a second embodiment of an OGV wheel in accordance with the invention; and

[0027] FIG. 6 shows a connection structure of a guide vane in a prior art OGV wheel.

DETAILED DESCRIPTION OF AN EMBODIMENT

[0028] FIG. 1 shows an intermediate casing OGV wheel sector made up of a hub 10 having two flanges 12 and 14, one upstream, the other downstream, of the outer shroud 18 of the intermediate casing (this shroud may be referred to as an intermediate casing shroud (ICS)), and of guide vanes 20 secured to the hub and to said ICS by a connection structure in accordance with the invention. Nevertheless, it should be observed that although the figure shows a guide vane downstream from a fan in diagrammatic manner, the invention is also applicable to other guide vanes, e.g. in a compressor first stage.

[0029] As shown in detail in FIGS. 2 and 3, the guide vane 20 made of polymer matrix composite material reinforced by fibers comprises an airfoil 200 extending radially relative to the main axis of the turbine engine and two platforms 202 and 204 positioned at respective radial ends of the airfoil, substantially perpendicularly thereto, each forming two half-platforms 202A, 202B; 204A, 204B on either side of the airfoil 200 (giving a total of four when distinguishing the bottom or vane root platform 202 and the top or vane tip platform 204) and connected thereto by connection fillets 206A, 206B; 208A, 208B. Preferably, the fibers are woven in three dimensions (3D) and these two half-platforms are obtained by non-interlinking in the 3D woven preform. Nevertheless, it is also possible to envisage using two-dimensional (2D) weaving, the 2D woven fibers then being arranged in superposed layers (plies) presenting local sideways folds in order to form the final 3D preform.

[0030] In the invention, at the root of the vane 20, fastening in the intermediate casing is performed by sandwiching each bottom half-platform 202A, 202B between a plane surface of the hub, e.g. a longitudinal arm 16 situated between the flanges 12 and 14, and a first backing plate 22 (shown in FIG. 1) that is ideally made of metal. The longitudinal arm 16 acting as reinforcement may for example be screw-fastened to the flanges 12 and 14 (as shown in FIG. 4), however in a variant that is not shown it is preferably cast integrally with said flanges. The backing plate 22 is bolted directly to the flanges 12 and 14 of the hub. The top half-platforms 204A and 204B are fastened to the intermediate casing shroud 18 in similar manner with a second backing plate likewise being fastened to the ICS by bolts. Specifically, and as shown in FIG. 3, this backing plate that is common to two adjacent OGVs may be replaced by two smaller backing plates 24A and 24B, each dedicated to one particular half-platform of an OGV.

[0031] The backing plates have side edges of a curved shape that is designed so as to fit closely against the connection fillets 206A, 206B, 208A, 208B. This imparts a significant improvement to the stiffness and mechanical strength properties of the OGV. Continuous contact between the two parts all along the chord of the vane optimizes the distribution of forces, thereby loading the entire section of the OGV.

[0032] As shown in the section of FIG. 4, a layer 26 of elastomer material is preferably interposed between the bottom platform 202 of the OGV and the plane surface 16 of the hub. The half-platforms 202A and 202B are thus sandwiched between the first metal backing plate of high stiffness that is fastened by bolts 28 to the upstream and downstream flanges of the hub and a layer of rubber that is less stiff, preferably being adhesively bonded on the plane surface, thereby imparting asymmetry in the behavior of the OGV in traction and compression. Because of this assembly configuration, force becomes distributed in natural manner within the OGV wheel on a priority basis towards the guide vanes that are stressed in traction (thus having stiff contacts between the vanes and the backing plates) instead of towards the vanes that are stressed in compression (and thus having less stiff contact with the rubber). The distribution of forces depends directly on geometrical characteristics (a function of the desired flexibility, of the desired prestress state, and of the estimated level of wear, . . . ) and on the selected material (stiffness, viscoelasticity rate, hardness, . . . ) as a function of the mechanical properties of the OGV (mainly traction and compression strengths).

[0033] Thus, if it is assumed that the ratio between the traction rupture stress threshold (Rmt) and the compression rupture stress threshold (Rmc) is R, it is appropriate to select the stiffness of the elastomer in such a manner that the force seen by the OGV stressed in compression is no more than 1/R times the force seen by the OGV stressed in traction, thereby imposing a ratio of R between the traction stiffness and the compression stiffness of the OGV. In compression, and in order to satisfy the above-explained principle, the flexibility of the elastomer is additional to that of the OGV so the stiffness of the elastomer is equal to Kt/(R1) where Kt is the stiffness of the OGV alone in traction.

[0034] Nevertheless, it should be observed that the elastomer material may be replaced by a metal or any other material that is softer than the material of the backing plate. Thus, by way of example, if the backing plate is made of quenched steel, the plane surface may be made of ordinary steel. The term softer covers smaller hardness and/or stiffness.

[0035] This type of fastening enables the 3D preform to be stressed constantly in the same direction (in the long direction of the airfoil). A warp/weft ratio that is uniform throughout the preform is then preferably selected giving priority to the warp direction, thereby correspondingly simplifying the steps of weaving and of shaping, while also giving rise to significant savings in fabrication costs.

[0036] Like the first elastomer material 26 interposed between the bottom platforms and the hub, a layer of a second elastomer material 30, which may optionally be identical to the first and which should be dimensioned in the manner described above, may also be interposed between the top platform 204 of the OGV 20 and the ICS 18 (see FIG. 3). Because of its outer wall nature, account may also be taken of the ability of the ICS to withstand chemical substances (oil, fuel, acid rain, . . . ).

[0037] Above, reference is often made to an OGV of the wheel having only a single airfoil. The number of such vanes in said wheel can be greater or smaller, e.g. about a dozen vanes to three dozen vanes.

[0038] FIG. 5 shows a wheel having an OGV doublet with a single preform. The composite OGV doublet is made up of a single preform 40 forming an O-shape. The backing plates 42 and 44 are then common to two adjacent vanes and are placed in the inter-OGV zone of a single vane doublet, thereby enabling the number of plates to be divided by two, thus obtaining a significant saving in weight. Furthermore, the continuity of the preform, which then does not present any non-interlinking as is needed for making half-platforms on either side of the vane (each vane then having only a half-platform extending the airfoil and running into the corresponding half-platform of the adjacent vane), serves to reinforce the mechanical strength of the OGV.