GB2250782A - Stator vane assembly - Google Patents

Abstract

A fluid flow machine stator vane assembly comprises an inner ring 1 and an outer ring 2 linked by a plurality of vanes 3A, the rings and vanes forming an integral structure. A further plurality of separate vanes 3B also link the inner and outer rings. The inner ends of vanes 3B locate in slots (5) (Fig 4) formed in the inner ring 1 while the outer ends of vanes 3B extend through slots 6 in ring 2 and are acted upon by springs 14 retained by a segmented ring 7 surrounding ring 2. The segments 8 of ring 7 are secured to studs (10) (Fig. 2 & 3) extending outwardly from vanes 3A. Vanes 3A may be metal while vanes 3B may be composite or ceramic and are replaceable if damaged. <IMAGE>

Description

STATOR VANE ASSEMBLY This invention relates to a stator vane assembly for use in a fluid flow machine, and particularly to an assembly for use in a gas turbine engine.

Known stator vane assemblies are formed by an outer metal ring and an inner metal ring linked by a plurality of metal vanes arranged between them like the spokes of a wheel, the rings and vanes forming an integral structure.

In the event of damage to any of the vanes, due to foreign objects in the fluid flow through the structure for example, the damaged vane is cut free from structure and a replacement vane welded into its place.

There are a number of problems with this technique, it is time consuming and difficult to ensure that the replacement vane is welded into the correct position and care must be taken to ensure that the cutting and welding operations do not weaken the metal rings and vanes due to the very high local temperatures involved.

Furthermore there is a general trend in the design of gas turbine engines for use in aircraft to replace metals with composite or ceramic materials because of their generally lower weight and higher temperature tolerance. If a ceramic or composite vane assembly as described above is produced and it suffers damage it must be replaced in its entirety because it is not possible to cut and rejoin ceramic or composite structures without loss of strength; this is clearly undesirable because of the high cost of complete replacement.

This invention was intended to at least partially overcome these problems.

In its broadest sense this invention provides a stator vane assembly having inner and outer rings linked by a plurality of vanes, the rings and some of the vanes forming an integral structure and the remaining vanes being discreet from that structure.

This invention provides a stator vane assembly comprising a first ring and a second ring, the first ring having a smaller radius than the second ring and the two rings being coaxial, the two rings being joined by a plurality of first vanes and a plurality of second vanes, the first vanes and the first and second rings being integral and the second vanes being separate.

The integral structure comprising the rings and first vanes can be made strong and rigid enough to support any loads acting on or through the assembly, while if damage occurs to one of the second vanes the vane can be easily removed and replaced because the second vanes are not integral with the rings.

A stator vane assembly embodying the invention will now be described by way of example only with reference to the accompanying diagrammatic figures in which: Figure 1 shows a stator vane assembly employing the invention; Figure 2 shows a section along the line A-A in figure 1; Figure 3 shows a section along the line B-B in figure 2; Figure 4 shows a section along the line E-E in figure 2, and Figure 5 shows a small part of figure 3 in more detail, similar parts having the same reference numerals throughout.

Referring to the figures a portion of a gas turbine stator vane assembly for use in a jet engine is shown.

The complete assembly would be a full circle, but the remainder of the circle will merely be repetitions of the section shown.

The assembly comprises an inner metal ring 1 and an outer metal ring 2 coaxial with the inner ring 1. The two rings 1 and 2 are linked by fifty-two radial vanes 3 evenly spaced around the circumferences of the two rings 1 and 2.

The radial vanes 3 are of two types, thirteen metal vanes 3A are integral with the inner and outer rings 1 and 2 respectively and are evenly spaced around the circumferences of the two rings 1 and 2. The rings 1 and 2 and vanes 3A form a rigid integral load bearing metal structure. In addition there are a further thirty-nine composite vanes 3B separate from this integral structure. Between each pair of integral vanes 3A three of the separate composite vanes 3B are situated evenly spaced from one another and the integral vanes 3A. As a result four equally sized and shaped gas flow passages 4 are defined by the vanes 3A and 3B and rings 1 and 2 between each pair of integral vanes 3A.

Since there are thirteen integral vanes 3A a total of fifty-two equally sized gas flow passages 4 are defined by the assembly as a whole.

Each of the composite vanes 3B fits at its innermost end into a slot 5 in the inner ring 1 and at its outermost end into a slot 6 in the outer ring 2. The slots 5 are recesses in the outer surface of the inner ring 1 and the innermost ends 3C of the vanes 3B are shaped to cooperate with the slots 5 to hold the vanes 3B in place relative to the inner ring 1. The slots 6 are wider than the slots 5 and are apertures passing through the outer ring 2, the radially outermost ends of the vanes 3B are shaped to cooperate with the slots 6 to hold the vanes 3B in place relative to the outer ring 2.

The size of the slots 6 is large enough for the innermost ends 3C of the vanes 3B to be passed through them. This allows each of the vanes 3B to be fitted by passing it through one of the slots 6 until its innermost end 3C contacts the inner ring 1 and then inserting the innermost end 3C of the vane 3B into a slot 5 and the outermost end 3D into a slot 6.

Each slot 6 is at the same circumferential position as one of the slots 5.

The vanes 3B are secured against movement in all directions other than radially and against twisting due to gas loads by their ends 3C and 3D cooperating with the slots 5 and 6 respectively, the vanes 3B also cannot move radially inwards because they bear against the bottoms of the slots 5 In order to prevent the vanes 3B moving radially outwards a securing ring 7 is attached to the outside of the outer ring 2.

The securing ring 7 is formed by a number of segments 8 each extending between two adjacent integral vanes 3A.

Extending radially outward from the end of each of the integral vanes 3A is a stud 9 bearing a threaded portion 10 at its radially outermost end. Each of the securing ring segments 8 has a first hole 11 passing through it at a first end 9A and a second hole 12 passing through it at a second end 8B and the segments 8 are fitted with two adjacent studs 9 each passing through one of the holes 8A and 8B. The ends 8A and 8B of the segments 8 are profiled so that the first end 8A of each segment 8 fits over the second end 8B of an adjacent segment 8 thus allowing the segments 8 to cooperate to form the ring 7. Each segment 8 has three recesses 13 in its innermost face, each overlying one of the slots 6.A resilient spring member 14 is situated within each recess 13 between the segment 8 and the end 3D of a vane 3B.

The securing ring segments 8 are held in place by nuts 15 on the threaded portions 10 of the studs 9. The nuts 15 urge the segments 8 against the outer ring 2 and compress the spring members 14 between the segments 8 and the vanes 3B, because the spring members 14 are resilient they in turn urge the vanes 3B radially inwards against the inner ring 1.

In the event of damage to one of the vanes 3B the nuts 15 and then the segments 8 are removed. The damaged vane 3B is then removed and a new vane 3B slid through the slot 6 and into the slot 5. The securing segments 8 and spring members 14 are then replaced and the nuts 15 replaced and tightened.

In the event of damage to one of the vanes 3A the damaged vane 3A being metal can be cut free from the rings 1 and 2 and a new vane 3A welded into place to replace it.

The assembly described has a total of fifty-two vanes of which a quarter are integral metal vanes, the invention is applicable to assemblies having any number of vanes, the proportion of the vanes which are integral may also be varied. In general the proportion of integral vanes should be as small as possible to reduce the chances that a damaged vane will be an integral one, however, there will generally be a minimum number of integral vanes required to give the assembly a required level of strength and rigidity.

All of the structure could be made of ceramics and/or composites rather than part metal and part composites.

Clearly the vanes 3B could be secured by means other than a segmented securing ring, such as individual retaining means.

Claims (6)

1 A stator vane assembly comprising a first ring and a second ring, the first ring having a smaller radius than the second ring and the two rings being coaxial, the two rings being joined by a plurality of first vanes and a plurality of second vanes, the first vanes and the first and second rings being integral and the second vanes being separate.

2 An assembly as claimed in claim 1 in which the vanes extend radially between the two rings.

3 An assembly as claimed in claim 1 or claim 2 in which the second vanes are held in place by cooperating with recesses in the first ring and apertures in the second ring.

4 An assembly as claimed in any preceding claim in which the rings and vanes are formed from a composite material.

5 An assembly as claimed in any of claims 1 to 3 in which the rings and vanes are formed from a ceramic material.

6 A stator vane assembly substantially as shown in or as described with reference to figures 1 to 5 of the accompanying drawings.